IPv6 Rapid Deployment on IPv4 Infrastructures (6rd) Protocol Specification

<pre> Internet Engineering Task Force (IETF) W. Townsley Request for Comments: 5969 O. Troan Category: Standards Track Cisco ISSN: 2070-1721 August 2010 IPv6 Rapid Deployment on IPv4 Infrastructures (6rd) -- Protocol Specification Abstract This document specifies an automatic tunneling mechanism tailored to advance deployment of IPv6 to end users via a service provider's IPv4 network infrastructure. Key aspects include automatic IPv6 prefix delegation to sites, stateless operation, simple provisioning, and service, which is equivalent to native IPv6 at the sites that are served by the mechanism. Status of This Memo This is an Internet Standards Track document. This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Further information on Internet Standards is available in Section 2 of RFC 5741. Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at http://www.rfc-editor.org/info/rfc5969. Copyright Notice Copyright (c) 2010 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Townsley & Troan Standards Track [Page 1] RFC 5969 6rd August 2010 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 2 2. Requirements Language . . . . . . . . . . . . . . . . . . . . 4 3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 4. 6rd Prefix Delegation . . . . . . . . . . . . . . . . . . . . 5 5. Troubleshooting and Traceability . . . . . . . . . . . . . . . 7 6. Address Selection . . . . . . . . . . . . . . . . . . . . . . 7 7. 6rd Configuration . . . . . . . . . . . . . . . . . . . . . . 7 7.1. Customer Edge Configuration . . . . . . . . . . . . . . . 8 7.1.1. 6rd DHCPv4 Option . . . . . . . . . . . . . . . . . . 9 7.2. Border Relay Configuration . . . . . . . . . . . . . . . . 10 8. Neighbor Unreachability Detection . . . . . . . . . . . . . . 11 9. IPv6 in IPv4 Encapsulation . . . . . . . . . . . . . . . . . . 12 9.1. Maximum Transmission Unit . . . . . . . . . . . . . . . . 13 9.2. Receiving Rules . . . . . . . . . . . . . . . . . . . . . 13 10. Transition Considerations . . . . . . . . . . . . . . . . . . 14 11. IPv6 Address Space Usage . . . . . . . . . . . . . . . . . . . 14 12. Security Considerations . . . . . . . . . . . . . . . . . . . 15 13. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 16 14. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 16 15. References . . . . . . . . . . . . . . . . . . . . . . . . . . 16 15.1. Normative References . . . . . . . . . . . . . . . . . . . 16 15.2. Informative References . . . . . . . . . . . . . . . . . . 17 1. Introduction The original idea and the name of the mechanism (6rd) described in [RFC5569] details a successful commercial "rapid deployment" of the 6rd mechanism by a residential service provider and is recommended reading. This document describes the 6rd mechanism, which has been extended for use in more general environments. Throughout this document, the term 6to4 is used to refer to the mechanism described in [RFC3056] and 6rd is the mechanism defined herein. 6rd specifies a protocol mechanism to deploy IPv6 to sites via a service provider's (SP's) IPv4 network. It builds on 6to4 [RFC3056], with the key differentiator that it utilizes an SP's own IPv6 address prefix rather than a well-known prefix (2002::/16). By using the SP's IPv6 prefix, the operational domain of 6rd is limited to the SP network and is under its direct control. From the perspective of customer sites and the IPv6 Internet at large, the IPv6 service provided is equivalent to native IPv6. The 6rd mechanism relies upon an algorithmic mapping between the IPv6 and IPv4 addresses that are assigned for use within the SP network. This mapping allows for automatic determination of IPv4 tunnel endpoints from IPv6 prefixes, allowing stateless operation of 6rd. Townsley & Troan Standards Track [Page 2] RFC 5969 6rd August 2010 6rd views the IPv4 network as a link layer for IPv6 and supports an automatic tunneling abstraction similar to the Non-Broadcast Multiple Access (NBMA) [RFC2491] model. A 6rd domain consists of 6rd Customer Edge (CE) routers and one or more 6rd Border Relays (BRs). IPv6 packets encapsulated by 6rd follow the IPv4 routing topology within the SP network among CEs and BRs. 6rd BRs are traversed only for IPv6 packets that are destined to or are arriving from outside the SP's 6rd domain. As 6rd is stateless, BRs may be reached using anycast for failover and resiliency (in a similar fashion to [RFC3068]). On the "customer-facing" (i.e., "LAN") side of a CE, IPv6 is implemented as it would be for any native IP service delivered by the SP, and further considerations for IPv6 operation on the LAN side of the CE is out of scope for this document. On the "SP-facing" (i.e., "WAN") side of the 6rd CE, the WAN interface itself, encapsulation over Ethernet, ATM or PPP, as well as control protocols such as PPPoE, IPCP, DHCP, etc. all remain unchanged from current IPv4 operation. Although 6rd was designed primarily to support IPv6 deployment to a customer site (such as a residential home network) by an SP, it can equally be applied to an individual IPv6 host acting as a CE. 6rd relies on IPv4 and is designed to deliver production-quality IPv6 alongside IPv4 with as little change to IPv4 networking and operations as possible. Native IPv6 deployment within the SP network itself may continue for the SP's own purposes while delivering IPv6 service to sites supported by 6rd. Once the SP network and operations can support fully native IPv6 access and transport, 6rd may be discontinued. 6rd utilizes the same encapsulation and base mechanism as 6to4 and could be viewed as a superset of 6to4 (6to4 could be achieved by setting the 6rd prefix to 2002::/16). Unlike 6to4, 6rd is for use only in an environment where a service provider closely manages the delivery of IPv6 service. 6to4 routes with the 2002::/16 prefix may exist alongside 6rd in the 6rd CE router, and doing so may offer some efficiencies when communicating directly with 6to4 routers. The 6rd link model can be extended to support IPv6 multicast. IPv6 multicast support is left for future consideration. How this mechanism should be used and other deployment and operational considerations are considered out of scope for this document. Townsley & Troan Standards Track [Page 3] RFC 5969 6rd August 2010 2. Requirements Language The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119 [RFC2119]. 3. Terminology 6rd prefix An IPv6 prefix selected by the service provider for use by a 6rd domain. There is exactly one 6rd prefix for a given 6rd domain. An SP may deploy 6rd with a single 6rd domain or multiple 6rd domains. 6rd Customer Edge (6rd CE) A device functioning as a Customer Edge router in a 6rd deployment. In a residential broadband deployment, this type of device is sometimes referred to as a "Residential Gateway" (RG) or "Customer Premises Equipment" (CPE). A typical 6rd CE serving a residential site has one WAN side interface, one or more LAN side interfaces, and a 6rd virtual interface. A 6rd CE may also be referred to simply as a "CE" within the context of 6rd. 6rd delegated prefix The IPv6 prefix calculated by the CE for use within the customer site by combining the 6rd prefix and the CE IPv4 address obtained via IPv4 configuration methods. This prefix can be considered logically equivalent to a DHCPv6 IPv6 delegated prefix [RFC3633]. 6rd domain A set of 6rd CEs and BRs connected to the same virtual 6rd link. A service provider may deploy 6rd with a single 6rd domain, or may utilize multiple 6rd domains. Each domain requires a separate 6rd prefix. CE LAN side The functionality of a 6rd CE that serves the "Local Area Network (LAN)" or "customer-facing" side of the CE. The CE LAN side interface is fully IPv6 enabled. Townsley & Troan Standards Track [Page 4] RFC 5969 6rd August 2010 CE WAN side The functionality of a 6rd CE that serves the "Wide Area Network (WAN)" or "Service Provider- facing" side of the CE. The CE WAN side is IPv4-only. 6rd Border Relay (BR) A 6rd-enabled router managed by the service provider at the edge of a 6rd domain. A Border Relay router has at least one of each of the following: an IPv4-enabled interface, a 6rd virtual interface acting as an endpoint for the 6rd IPv6 in IPv4 tunnel, and an IPv6 interface connected to the native IPv6 network. A 6rd BR may also be referred to simply as a "BR" within the context of 6rd. BR IPv4 address The IPv4 address of the 6rd Border Relay for a given 6rd domain. This IPv4 address is used by the CE to send packets to a BR in order to reach IPv6 destinations outside of the 6rd domain. 6rd virtual interface Internal multi-point tunnel interface where 6rd encapsulation and decapsulation of IPv6 packets inside IPv4 occurs. A typical CE or BR implementation requires only one 6rd virtual interface. A BR operating in multiple 6rd domains may require more than one 6rd virtual interface, but no more than one per 6rd domain. CE IPv4 address The IPv4 address given to the CE as part of normal IPv4 Internet access (i.e., configured via DHCP, PPP, or otherwise). This address may be global or private [RFC1918] within the 6rd domain. This address is used by a 6rd CE to create the 6rd delegated prefix as well as to send and receive IPv4-encapsulated IPv6 packets. 4. 6rd Prefix Delegation The 6rd delegated prefix for use at a customer site is created by combining the 6rd prefix and all or part of the CE IPv4 address. From these elements, the 6rd delegated prefix is automatically created by the CE for the customer site when IPv4 service is obtained. This 6rd delegated prefix is used in the same manner as a prefix obtained via DHCPv6 prefix delegation [RFC3633]. Townsley & Troan Standards Track [Page 5] RFC 5969 6rd August 2010 In 6to4, a similar operation is performed by incorporating an entire IPv4 address at a fixed location following a well-known /16 IPv6 prefix. In 6rd, the IPv6 prefix as well as the position and number of bits of the IPv4 address incorporated varies from one 6rd domain to the next. 6rd allows the SP to adjust the size of the 6rd prefix, how many bits are used by the 6rd mechanism, and how many bits are left to be delegated to customer sites. To allow for stateless address auto-configuration on the CE LAN side, a 6rd delegated prefix SHOULD be /64 or shorter. The 6rd delegated prefix is created by concatenating the 6rd prefix and a consecutive set of bits from the CE IPv4 address in order. The length of the 6rd delegated prefix is equal to length of the 6rd prefix (n) plus the number of bits from the CE IPv4 address (o). The figure shows the format of an IPv6 address (Section 2.5.4 of [RFC4291]) with a 6rd prefix and an embedded CE IPv4 address: | n bits | o bits | m bits | 128-n-o-m bits | +---------------+--------------+-----------+------------------------+ | 6rd prefix | IPv4 address | subnet ID | interface ID | +---------------+--------------+-----------+------------------------+ |<--- 6rd delegated prefix --->| Figure 1 For example, if the 6rd prefix is /32 and 24 bits of the CE IPv4 address is used (e.g., all CE IPv4 addresses can be aggregated by a 10.0.0.0/8), then the size of the 6rd delegated prefix for each CE is automatically calculated to be /56 (32 + 24 = 56). Embedding less than the full 32 bits of a CE IPv4 address is possible only when an aggregated block of IPv4 addresses is available for a given 6rd domain. This may not be practical with global IPv4 addresses, but is quite likely in a deployment where private addresses are being assigned to CEs. If private addresses overlap within a given 6rd deployment, the deployment may be divided into separate 6rd domains, likely along the same topology lines the NAT- based IPv4 deployment itself would require. In this case, each domain is addressed with a different 6rd prefix. Each 6rd domain may use a different encoding of the embedded IPv4 address, even within the same service provider. For example, if multiple IPv4 address blocks with different levels of aggregation are used at the same service provider, the number of IPv4 bits needed to encode the 6rd delegated prefix may vary between each block. In this case, different 6rd prefixes, and hence separate 6rd domains, may be used to support the different encodings. Townsley & Troan Standards Track [Page 6] RFC 5969 6rd August 2010 Since 6rd delegated prefixes are selected algorithmically from an IPv4 address, changing the IPv4 address will cause a change in the IPv6 delegated prefix which would ripple through the site's network and could be disruptive. As such, it is recommended that the service provider assign CE IPv4 addresses with relatively long lifetimes. 6rd IPv6 address assignment, and hence the IPv6 service itself, is tied to the IPv4 address lease; thus, the 6rd service is also tied to this in terms of authorization, accounting, etc. For example, the 6rd delegated prefix has the same lifetime as its associated IPv4 address. The prefix lifetimes advertised in Router Advertisements or used by DHCP on the CE LAN side MUST be equal to or shorter than the IPv4 address lease time. If the IPv4 lease time is not known, the lifetime of the 6rd delegated prefix SHOULD follow the defaults specified in [RFC4861]. 5. Troubleshooting and Traceability A 6rd IPv6 address and associated IPv4 address for a given customer can always be determined algorithmically by the service provider that operates the given 6rd domain. This may be useful for referencing logs and other data at a service provider that may have more robust operational tools for IPv4 than IPv6. This also allows IPv4 data path, node, and endpoint monitoring to be applicable to IPv6. The 6rd CE and BR SHOULD support the IPv6 Subnet-Router anycast address [RFC4291] for its own 6rd delegated prefix. This allows, for example, IPv6 ICMP echo messages to be sent to the 6rd virtual interface itself for additional troubleshooting of the internal operation of 6rd at a given CE or BR. In the case of the BR, the IPv4 address used to calculate the 6rd delegated prefix is the configured BR IPv4 address. 6. Address Selection All addresses assigned from 6rd delegated prefixes should be treated as native IPv6. No changes to the source address selection or destination address selection policy table [RFC3484] are necessary. 7. 6rd Configuration For a given 6rd domain, the BR and CE MUST be configured with the following four 6rd elements. The configured values for these four 6rd elements are identical for all CEs and BRs within a given 6rd domain. Townsley & Troan Standards Track [Page 7] RFC 5969 6rd August 2010 IPv4MaskLen The number of high-order bits that are identical across all CE IPv4 addresses within a given 6rd domain. For example, if there are no identical bits, IPv4MaskLen is 0 and the entire CE IPv4 address is used to create the 6rd delegated prefix. If there are 8 identical bits (e.g., the Private IPv4 address range 10.0.0.0/8 is being used), IPv4MaskLen is equal to 8 and IPv4MaskLen high-order bits are stripped from the IPv4 address before constructing the corresponding 6rd delegated prefix. 6rdPrefix The 6rd IPv6 prefix for the given 6rd domain. 6rdPrefixLen The length of the 6rd IPv6 prefix for the given 6rd domain. 6rdBRIPv4Address The IPv4 address of the 6rd Border Relay for a given 6rd domain. 7.1. Customer Edge Configuration The four 6rd elements are set to values that are the same across all CEs within a 6rd domain. The values may be configured in a variety of manners, including provisioning methods such as the Broadband Forum's "TR-69" [TR069] Residential Gateway management interface, an XML-based object retrieved after IPv4 connectivity is established, a DNS record, an SMIv2 MIB [RFC2578], PPP IPCP, or manual configuration by an administrator. This document describes how to configure the necessary parameters via a single DHCP option. A CE that allows IPv4 configuration by DHCP SHOULD implement this option. Other configuration and management methods may use the format described by this option for consistency and convenience of implementation on CEs that support multiple configuration methods. The only remaining provisioning information the CE requires in order to calculate the 6rd delegated prefix and enable IPv6 connectivity is an IPv4 address for the CE. This CE IPv4 address is configured as part of obtaining IPv4 Internet access (i.e., configured via DHCP, PPP, or otherwise). This address may be global or private [RFC1918] within the 6rd domain. A single 6rd CE MAY be connected to more than one 6rd domain, just as any router may have more than one IPv6-enabled service provider facing interface and more than one set of associated delegated prefixes assigned by DHCPv6 prefix delegation or other means. Each Townsley & Troan Standards Track [Page 8] RFC 5969 6rd August 2010 domain a given CE operates within would require its own set of 6rd configuration elements and would generate its own 6rd delegated prefix. 7.1.1. 6rd DHCPv4 Option 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | OPTION_6RD | option-length | IPv4MaskLen | 6rdPrefixLen | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | 6rdPrefix | | (16 octets) | | | | | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 6rdBRIPv4Address(es) | . . . . . . +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 2 option-code OPTION_6RD (212) option-length The length of the DHCP option in octets (22 octets with one BR IPv4 address). IPv4MaskLen The number of high-order bits that are identical across all CE IPv4 addresses within a given 6rd domain. This may be any value between 0 and 32. Any value greater than 32 is invalid. 6rdPrefixLen The IPv6 prefix length of the SP's 6rd IPv6 prefix in number of bits. For the purpose of bounds checking by DHCP option processing, the sum of (32 - IPv4MaskLen) + 6rdPrefixLen MUST be less than or equal to 128. 6rdBRIPv4Address One or more IPv4 addresses of the 6rd Border Relay(s) for a given 6rd domain. Townsley & Troan Standards Track [Page 9] RFC 5969 6rd August 2010 6rdPrefix The service provider's 6rd IPv6 prefix represented as a 16-octet IPv6 address. The bits in the prefix after the 6rdPrefixlen number of bits are reserved and MUST be initialized to zero by the sender and ignored by the receiver. The CE MUST include a Parameter Request List Option [RFC2132] for the OPTION_6RD. Because the OPTION_6RD contains one IPv4MaskLen/ 6rdPrefixLen/6rdPrefix block, and because DHCP cannot convey more than one instance of an option, OPTION_6RD is limited to provision at most a single 6rd domain. Provisioning of a CE router connected to multiple 6rd domains is outside the scope of this protocol specification. The presence of the OPTION_6RD DHCP option is an indication of the availability of the 6rd service. By default, receipt of a valid 6rd DHCP option by a 6rd-capable CE results in configuration of the 6rd virtual interface and associated delegated prefix for use on the CE's LAN side. The CE MUST be able to configure the 6rd mechanism to be disabled, in which case the 6rd DHCP option, if received, is silently ignored. A detailed description of CE behavior using multiple BR IPv4 addresses is left for future consideration. In such a case, a CE MUST support at least one BR IPv4 address and MAY support more than one. When 6rd is enabled, a typical CE router will install a default route to the BR, a black hole route for the 6rd delegated prefix, and routes for any LAN side assigned and advertised prefixes. For example, using a CE IPv4 address of 10.100.100.1, a BR IPv4 address of 10.0.0.1, an IPv4MaskLen of 8, 2001:db8::/32 as the 6rdPrefix, and one /64 prefix assigned to a LAN side interface, a typical CE routing table will look like: ::/0 -> 6rd-virtual-int0 via 2001:db8:0:100:: (default route) 2001:db8::/32 -> 6rd-virtual-int0 (direct connect to 6rd) 2001:db8:6464:100::/56 -> Null0 (delegated prefix null route) 2001:db8:6464:100::/64 -> Ethernet0 (LAN interface) 7.2. Border Relay Configuration The 6rd BR MUST be configured with the same 6rd elements as the 6rd CEs operating within the same domain. For increased reliability and load balancing, the BR IPv4 address may be an anycast address shared across a given 6rd domain. As 6rd is stateless, any BR may be used at any time. If the BR IPv4 address is Townsley & Troan Standards Track [Page 10] RFC 5969 6rd August 2010 anycast the relay MUST use this anycast IPv4 address as the source address in packets relayed to CEs. Since 6rd uses provider address space, no specific routes need to be advertised externally for 6rd to operate, neither in IPv6 nor IPv4 BGP. However, if anycast is used for the 6rd IPv4 relays, the anycast addresses must be advertised in the service provider's IGP. 8. Neighbor Unreachability Detection Neighbor Unreachability Detection (NUD) for tunnels is described in Section 3.8 of [RFC4213]. In 6rd, all CEs and BRs can be considered as connected to the same virtual link and therefore neighbors to each other. This section describes how to utilize neighbor unreachability detection without negatively impacting the scalability of a 6rd deployment. A typical 6rd deployment may consist of a very large number of CEs within the same domain. Reachability between CEs is based on IPv4 routing, and sending NUD or any periodic packets between 6rd CE devices beyond isolated troubleshooting of the 6rd mechanism is NOT RECOMMENDED. While reachability detection between a given 6rd CE and BR is not necessary for the proper operation of 6rd, in cases where a CE has alternate paths for BR reachability to choose from, it could be useful. Sending NUD messages to a BR, in particular periodic messages from a very large number of CEs, could result in overloading of the BR control message processing path, negatively affecting scalability of the 6rd deployment. Instead, a CE that needs to determine BR reachability MUST utilize a method that allows reachability detection packets to follow a typical data forwarding path without special processing by the BR. One such method is described below. 1. The CE constructs a payload of any size and content to be sent to the BR (e.g., a zero-length null payload, a padded payload designed to test a certain MTU, a NUD message, etc.). The exact format of the message payload is not important as the BR will not be processing it directly. 2. The desired payload is encapsulated with the inner IPv6 and outer IPv4 headers as follows: * The IPv6 destination address is set to an address from the CE's 6rd delegated prefix that is assigned to a virtual interface on the CE. Townsley & Troan Standards Track [Page 11] RFC 5969 6rd August 2010 * The IPv6 source address is set to an address from the CE's 6rd delegated prefix as well, including the same as used for the IPv6 destination address. * The IPv4 header is then added as it normally would be for any packet destined for the BR. That is, the IPv4 destination address is that of the BR, and the source address is the CE IPv4 address. 3. The CE sends the constructed packet out the interface on which BR reachability is being monitored. On successful receipt at the BR, the BR MUST decapsulate and forward the packet normally. That is, the IPv4 header is decapsulated normally, revealing the IPv6 destination as the CE, which in turn results in the packet being forwarded to that CE via the 6rd mechanism (i.e., the IPv4 destination is that of the CE that originated the packet, and the IPv4 source is that of the BR). 4. Arrival of the constructed IPv6 packet at the CE's IPv6 address completes one round trip to and from the BR, without causing the BR to process the message outside of its normal data forwarding path. The CE then processes the IPv6 packet accordingly (updating keepalive timers, metrics, etc.). The payload may be empty or could contain values that are meaningful to the CE. Sending a proper NUD message could be convenient for some implementations (note that the BR will decrement the IPv6 hop limit). Since the BR forwards the packet as any other data packet without any processing of the payload itself, the format of the payload is left as a choice to the implementer. 9. IPv6 in IPv4 Encapsulation IPv6 in IPv4 encapsulation and forwarding manipulations (e.g., handling packet markings, checksumming, etc.) is performed as specified in Section 3.5 of "Basic Transition Mechanisms for IPv6 Hosts and Routers" [RFC4213], which is the same mechanism used by 6to4 [RFC3056]. ICMPv4 errors are handled as specified in Section 3.4 of [RFC4213]. By default, the IPv6 Traffic Class field MUST be copied to the IPv4 ToS (Type of Service) field. This default behavior MAY be overridden by configuration. See [RFC2983] and [RFC3168] for further information related to IP Differentiated Services and tunneling. IPv6 packets from a CE are encapsulated in IPv4 packets when they leave the site via its CE WAN side interface. The CE IPv4 address MUST be configured to send and receive packets on this interface. Townsley & Troan Standards Track [Page 12] RFC 5969 6rd August 2010 The 6rd link is modeled as an NBMA link similar to other automatic IPv6 in IPv4 tunneling mechanisms like [RFC5214], with all 6rd CEs and BRs defined as off-link neighbors from one other. The link-local address of a 6rd virtual interface performing the 6rd encapsulation would, if needed, be formed as described in Section 3.7 of [RFC4213]. However, no communication using link-local addresses will occur. 9.1. Maximum Transmission Unit Maximum transmission unit (MTU) and fragmentation issues for IPv6 in IPv4 tunneling are discussed in detail in Section 3.2 of RFC 4213 [RFC4213]. 6rd's scope is limited to a service provider network. IPv4 Path MTU discovery MAY be used to adjust the MTU of the tunnel as described in Section 3.2.2 of RFC 4213 [RFC4213], or the 6rd Tunnel MTU might be explicitly configured. The use of an anycast source address could lead to any ICMP error message generated on the path being sent to a different BR. Therefore, using dynamic tunnel MTU Section 3.2.2 of [RFC4213] is subject to IPv4 Path MTU blackholes. Multiple BRs using the same anycast source address could send fragmented packets to the same IPv6 CE at the same time. If the fragmented packets from different BRs happen to use the same fragment ID, incorrect reassembly might occur. For this reason, a BR using an anycast source address MUST set the IPv4 Don't Fragment flag. If the MTU is well-managed such that the IPv4 MTU on the CE WAN side interface is set so that no fragmentation occurs within the boundary of the SP, then the 6rd Tunnel MTU should be set to the known IPv4 MTU minus the size of the encapsulating IPv4 header (20 bytes). For example, if the IPv4 MTU is known to be 1500 bytes, the 6rd Tunnel MTU might be set to 1480 bytes. Absent more specific information, the 6rd Tunnel MTU SHOULD default to 1280 bytes. 9.2. Receiving Rules In order to prevent spoofing of IPv6 addresses, the 6rd BR and CE MUST validate the embedded IPv4 source address of the encapsulated IPv6 packet with the IPv4 source address it is encapsulated by according to the configured parameters of the 6rd domain. If the two source addresses do not match, the packet MUST be dropped and a counter incremented to indicate that a potential spoofing attack may be underway. Additionally, a CE MUST allow forwarding of packets sourced by the configured BR IPv4 address. Townsley & Troan Standards Track [Page 13] RFC 5969 6rd August 2010 By default, the CE router MUST drop packets received on the 6rd virtual interface (i.e., after decapsulation of IPv4) for IPv6 destinations not within its own 6rd delegated prefix. 10. Transition Considerations An SP network can migrate to IPv6 at its own pace with little or no effect on customers being provided IPv6 via 6rd. When native IPv6 connectivity is available, an administrator can choose to disable 6rd. The SP can choose to provision a separate IPv6 address block for native service, or reuse the 6rd prefix block itself. If the SP uses a separate address block, moving from 6rd to native IPv6 is seen as a normal IPv6 renumbering event for the customer. Renumbering may also be avoided by injecting the 6rd delegated prefix into the SP's IPv6 routing domain. Further considerations with regards to transitioning from 6rd to native IPv6 are not covered in this protocol specification. 11. IPv6 Address Space Usage As 6rd uses service-provider address space, 6rd uses the normal address delegation a service provider gets from its Regional Internet Registry (RIR) and no global allocation of a single 6rd IANA-assigned address block like the 6to4 2002::/16 is needed. The service provider's prefix must be short enough to encode the unique bits of all IPv4 addresses within a given 6rd domain and still provide enough IPv6 address space to the residential site. Assuming a worst case scenario using the full 32 bits for the IPv4 address, assigning a /56 for customer sites would mean that each service provider using 6rd would require a /24 for 6rd in addition to other IPv6 addressing needs. Assuming that 6rd would be stunningly successful and taken up by almost all Autonomous System (AS) number holders (32K today), then the total address usage of 6rd would be equivalent to a /9. If the SP instead delegated /60s to sites, the service provider would require a /28, and the total global address consumption by 6rd would be equivalent to a /13. Again, this assumes that 6rd is used by all AS number holders in the IPv4 Internet today at the same time, that none have used any of 6rd's address compression techniques, and that none have moved to native IPv6 and reclaimed the 6rd space that was being used for other purposes. To alleviate concerns about address usage, 6rd allows for leaving out redundant IPv4 prefix bits in the encoding of the IPv4 address inside the 6rd IPv6 address. This is most useful where the IPv4 address space is very well aggregated. For example, to provide each customer Townsley & Troan Standards Track [Page 14] RFC 5969 6rd August 2010 with a /60, if a service provider has all its IPv4 customers under a /12 then only 20 bits needs to be used to encode the IPv4 address and the service provider would only need a /40 IPv6 allocation for 6rd. If private address space is used, then a 10/8 would require a /36. If multiple 10/8 domains are used, then up to 16 could be supported within a /32. If a service provider has a non-aggregatable IPv4 space and requiring the use of the full 32-bit IPv4 address in the encoding of the 6rd IPv6 address, the 6rd prefix MUST be no longer than /32 in order to offer a 6rd delegated prefix of at least /64. The 6rd address block can be reclaimed when all users of it have transitioned to native IPv6 service. This may require renumbering of customer sites and use of additional address space during the transition period. 12. Security Considerations A 6to4 relay router as specified in [RFC3056] can be used as an open relay. It can be used to relay IPv6 traffic and as a traffic anonymizer. By restricting the 6rd domain to within a provider network, a CE only needs to accept packets from a single or small set of known 6rd BR IPv4 addresses. As such, many of the threats against 6to4 as described in [RFC3964] do not apply. When applying the receiving rules in Section 9.2, IPv6 packets are as well protected against spoofing as IPv4 packets are within an SP network. A malicious user that is aware of a 6rd domain and the BR IPv4 address could use this information to construct a packet that would cause a Border Relay to reflect tunneled packets outside of the domain that it is serving. If the attacker constructs the packet accordingly and can inject a packet with an IPv6 source address that looks as if it originates from within another 6rd domain, forwarding loops between 6rd domains may be created, allowing the malicious user to launch a packet amplification attack between 6rd domains [RoutingLoop]. One possible mitigation for this is to simply not allow the BR IPv4 address to be reachable from outside the SP's 6rd domain. In this case, carefully constructed IPv6 packets still could be reflected off a single BR, but the looping condition will not occur. Tunneled packets with the BR IPv4 address as the source address might also be filtered to prohibit 6rd tunnels from exiting the 6rd domain. Townsley & Troan Standards Track [Page 15] RFC 5969 6rd August 2010 To avoid forwarding loops via other internal relays, the BR should employ outgoing and incoming IPv4 packets filters, filtering out all known relay addresses for internal 6rd BRs, ISATAP routers, or 6to4 relays, including the well-known anycast address space for 6to4. Another possible mitigation to the routing loop issue is described in [V6OPS-LOOPS]. The BR MUST install a null route [RFC4632] for its 6rd delegated prefix created based on its BR IPv4 address, with the exception of the IPv6 Subnet-Router anycast address. 13. IANA Considerations IANA assigned a new DHCP Option code point for OPTION_6RD (212) with a data length of 18 + N (OPTION_6RD with N/4 6rd BR addresses). 14. Acknowledgements This RFC is based on Remi Despres' original idea described in [RFC5569] and the work done by Rani Assaf, Alexandre Cassen, and Maxime Bizon at Free Telecom. Brian Carpenter and Keith Moore documented 6to4, which all of this work is based upon. We thank Fred Templin for his review and contributions, and for sharing his experience with ISATAP. Review and encouragement have been provided by many others and in particular Chris Chase, Thomas Clausen, Wouter Cloetens, Wojciech Dec, Bruno Decraene, Remi Despres, Alain Durand, Washam Fan, Martin Gysi, David Harrington, Jerry Huang, Peter McCann, Alexey Melnikov, Dave Thaler, Eric Voit, and David Ward. 15. References 15.1. Normative References [RFC1918] Rekhter, Y., Moskowitz, R., Karrenberg, D., Groot, G., and E. Lear, "Address Allocation for Private Internets", BCP 5, RFC 1918, February 1996. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC2132] Alexander, S. and R. Droms, "DHCP Options and BOOTP Vendor Extensions", RFC 2132, March 1997. [RFC2491] Armitage, G., Schulter, P., Jork, M., and G. Harter, "IPv6 over Non-Broadcast Multiple Access (NBMA) networks", RFC 2491, January 1999. Townsley & Troan Standards Track [Page 16] RFC 5969 6rd August 2010 [RFC3056] Carpenter, B. and K. Moore, "Connection of IPv6 Domains via IPv4 Clouds", RFC 3056, February 2001. [RFC3168] Ramakrishnan, K., Floyd, S., and D. Black, "The Addition of Explicit Congestion Notification (ECN) to IP", RFC 3168, September 2001. [RFC4213] Nordmark, E. and R. Gilligan, "Basic Transition Mechanisms for IPv6 Hosts and Routers", RFC 4213, October 2005. [RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing Architecture", RFC 4291, February 2006. [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, September 2007. 15.2. Informative References [RFC2578] McCloghrie, K., Ed., Perkins, D., Ed., and J. Schoenwaelder, Ed., "Structure of Management Information Version 2 (SMIv2)", STD 58, RFC 2578, April 1999. [RFC2983] Black, D., "Differentiated Services and Tunnels", RFC 2983, October 2000. [RFC3068] Huitema, C., "An Anycast Prefix for 6to4 Relay Routers", RFC 3068, June 2001. [RFC3484] Draves, R., "Default Address Selection for Internet Protocol version 6 (IPv6)", RFC 3484, February 2003. [RFC3633] Troan, O. and R. Droms, "IPv6 Prefix Options for Dynamic Host Configuration Protocol (DHCP) version 6", RFC 3633, December 2003. [RFC3964] Savola, P. and C. Patel, "Security Considerations for 6to4", RFC 3964, December 2004. [RFC4632] Fuller, V. and T. Li, "Classless Inter-domain Routing (CIDR): The Internet Address Assignment and Aggregation Plan", BCP 122, RFC 4632, August 2006. [RFC5214] Templin, F., Gleeson, T., and D. Thaler, "Intra-Site Automatic Tunnel Addressing Protocol (ISATAP)", RFC 5214, March 2008. Townsley & Troan Standards Track [Page 17] RFC 5969 6rd August 2010 [RFC5569] Despres, R., "IPv6 Rapid Deployment on IPv4 Infrastructures (6rd)", RFC 5569, January 2010. [RoutingLoop] Nakibly and Arov, "Routing Loop Attacks using IPv6 Tunnels", August 2009, <http://www.usenix.org/event/ woot09/tech/full_papers/nakibly.pdf>. [TR069] "TR-069, CPE WAN Management Protocol v1.1, Version: Issue 1 Amendment 2", December 2007. [V6OPS-LOOPS] Nakibly, G. and F. Templin, "Routing Loop Attack using IPv6 Automatic Tunnels: Problem Statement and Proposed Mitigations", Work in Progress, May 2010. Authors' Addresses Mark Townsley Cisco Paris, France EMail: mark@townsley.net Ole Troan Cisco Bergen, Norway EMail: ot@cisco.com Townsley & Troan Standards Track [Page 18] </pre>

IPv6 Rapid Deployment on IPv4 Infrastructures (6rd) Protocol Specification

Internet Engineering Task Force (IETF) W. Townsley Request for Comments: 5969 ...

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IPv6 Addressing of IPv4/IPv6 Translators

<pre> Internet Engineering Task Force (IETF) C. Bao Request for Comments: 6052 CERNET Center/Tsinghua University Updates: 4291 C. Huitema Category: Standards Track Microsoft Corporation ISSN: 2070-1721 M. Bagnulo UC3M M. Boucadair France Telecom X. Li CERNET Center/Tsinghua University October 2010 IPv6 Addressing of IPv4/IPv6 Translators Abstract This document discusses the algorithmic translation of an IPv6 address to a corresponding IPv4 address, and vice versa, using only statically configured information. It defines a well-known prefix for use in algorithmic translations, while allowing organizations to also use network-specific prefixes when appropriate. Algorithmic translation is used in IPv4/IPv6 translators, as well as other types of proxies and gateways (e.g., for DNS) used in IPv4/IPv6 scenarios. Status of This Memo This is an Internet Standards Track document. This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Further information on Internet Standards is available in Section 2 of RFC 5741. Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at http://www.rfc-editor.org/info/rfc6052. Bao, et al. Standards Track [Page 1] RFC 6052 IPv6 Addressing of IPv4/IPv6 Translators October 2010 Copyright Notice Copyright (c) 2010 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1. Applicability Scope . . . . . . . . . . . . . . . . . . . 3 1.2. Conventions . . . . . . . . . . . . . . . . . . . . . . . 4 1.3. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4 2. IPv4-Embedded IPv6 Address Prefix and Format . . . . . . . . . 5 2.1. Well-Known Prefix . . . . . . . . . . . . . . . . . . . . 5 2.2. IPv4-Embedded IPv6 Address Format . . . . . . . . . . . . 5 2.3. Address Translation Algorithms . . . . . . . . . . . . . . 7 2.4. Text Representation . . . . . . . . . . . . . . . . . . . 7 3. Deployment Guidelines . . . . . . . . . . . . . . . . . . . . 8 3.1. Restrictions on the Use of the Well-Known Prefix . . . . . 8 3.2. Impact on Inter-Domain Routing . . . . . . . . . . . . . . 8 3.3. Choice of Prefix for Stateless Translation Deployments . . 9 3.4. Choice of Prefix for Stateful Translation Deployments . . 11 4. Design Choices . . . . . . . . . . . . . . . . . . . . . . . . 12 4.1. Choice of Suffix . . . . . . . . . . . . . . . . . . . . . 12 4.2. Choice of the Well-Known Prefix . . . . . . . . . . . . . 13 5. Security Considerations . . . . . . . . . . . . . . . . . . . 14 5.1. Protection against Spoofing . . . . . . . . . . . . . . . 14 5.2. Secure Configuration . . . . . . . . . . . . . . . . . . . 15 5.3. Firewall Configuration . . . . . . . . . . . . . . . . . . 15 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 16 8. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 16 9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 17 9.1. Normative References . . . . . . . . . . . . . . . . . . . 17 9.2. Informative References . . . . . . . . . . . . . . . . . . 17 Bao, et al. Standards Track [Page 2] RFC 6052 IPv6 Addressing of IPv4/IPv6 Translators October 2010 1. Introduction This document is part of a series of IPv4/IPv6 translation documents. A framework for IPv4/IPv6 translation is discussed in [v4v6-FRAMEWORK], including a taxonomy of scenarios that will be used in this document. Other documents specify the behavior of various types of translators and gateways, including mechanisms for translating between IP headers and other types of messages that include IP addresses. This document specifies how an individual IPv6 address is translated to a corresponding IPv4 address, and vice versa, in cases where an algorithmic mapping is used. While specific types of devices are used herein as examples, it is the responsibility of the specification of such devices to reference this document for algorithmic mapping of the addresses themselves. Section 2 describes the prefixes and the format of "IPv4-embedded IPv6 addresses", i.e., IPv6 addresses in which 32 bits contain an IPv4 address. This format is common to both "IPv4-converted" and "IPv4-translatable" IPv6 addresses. This section also defines the algorithms for translating addresses, and the text representation of IPv4-embedded IPv6 addresses. Section 3 discusses the choice of prefixes, the conditions in which they can be used, and the use of IPv4-embedded IPv6 addresses with stateless and stateful translation. Section 4 provides a summary of the discussions behind two specific design decisions, the choice of a null suffix and the specific value of the selected prefix. Section 5 discusses security concerns. In some scenarios, a dual-stack host will unnecessarily send its traffic through an IPv6/IPv4 translator. This can be caused by the host's default address selection algorithm [RFC3484], referrals, or other reasons. Optimizing these scenarios for dual-stack hosts is for future study. 1.1. Applicability Scope This document is part of a series defining address translation services. We understand that the address format could also be used by other interconnection methods between IPv6 and IPv4, e.g., methods based on encapsulation. If encapsulation methods are developed by the IETF, we expect that their descriptions will document their specific use of IPv4-embedded IPv6 addresses. Bao, et al. Standards Track [Page 3] RFC 6052 IPv6 Addressing of IPv4/IPv6 Translators October 2010 1.2. Conventions The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119 [RFC2119]. 1.3. Terminology This document makes use of the following terms: Address translator: any entity that has to derive an IPv4 address from an IPv6 address or vice versa. This applies not only to devices that do IPv4/IPv6 packet translation, but also to other entities that manipulate addresses, such as name resolution proxies (e.g., DNS64 [DNS64]) and possibly other types of Application Layer Gateways (ALGs). IPv4-converted IPv6 addresses: IPv6 addresses used to represent IPv4 nodes in an IPv6 network. They are a variant of IPv4-embedded IPv6 addresses and follow the format described in Section 2.2. IPv4-embedded IPv6 addresses: IPv6 addresses in which 32 bits contain an IPv4 address. Their format is described in Section 2.2. IPv4/IPv6 translator: an entity that translates IPv4 packets to IPv6 packets, and vice versa. It may do "stateless" translation, meaning that there is no per-flow state required, or "stateful" translation, meaning that per-flow state is created when the first packet in a flow is received. IPv4-translatable IPv6 addresses: IPv6 addresses assigned to IPv6 nodes for use with stateless translation. They are a variant of IPv4-embedded IPv6 addresses and follow the format described in Section 2.2. Network-Specific Prefix: an IPv6 prefix assigned by an organization for use in algorithmic mapping. Options for the Network-Specific Prefix are discussed in Sections 3.3 and 3.4. Well-Known Prefix: the IPv6 prefix defined in this document for use in an algorithmic mapping. Bao, et al. Standards Track [Page 4] RFC 6052 IPv6 Addressing of IPv4/IPv6 Translators October 2010 2. IPv4-Embedded IPv6 Address Prefix and Format 2.1. Well-Known Prefix This document reserves a "Well-Known Prefix" for use in an algorithmic mapping. The value of this IPv6 prefix is: 64:ff9b::/96 2.2. IPv4-Embedded IPv6 Address Format IPv4-converted IPv6 addresses and IPv4-translatable IPv6 addresses follow the same format, described here as the IPv4-embedded IPv6 address Format. IPv4-embedded IPv6 addresses are composed of a variable-length prefix, the embedded IPv4 address, and a variable- length suffix, as presented in the following diagram, in which PL designates the prefix length: +--+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+ |PL| 0-------------32--40--48--56--64--72--80--88--96--104---------| +--+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+ |32| prefix |v4(32) | u | suffix | +--+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+ |40| prefix |v4(24) | u |(8)| suffix | +--+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+ |48| prefix |v4(16) | u | (16) | suffix | +--+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+ |56| prefix |(8)| u | v4(24) | suffix | +--+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+ |64| prefix | u | v4(32) | suffix | +--+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+ |96| prefix | v4(32) | +--+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+ Figure 1 In these addresses, the prefix shall be either the "Well-Known Prefix" or a "Network-Specific Prefix" unique to the organization deploying the address translators. The prefixes can only have one of the following lengths: 32, 40, 48, 56, 64, or 96. (The Well-Known Prefix is 96 bits long, and can only be used in the last form of the table.) Various deployments justify different prefix lengths with Network- Specific Prefixes. The trade-off between different prefix lengths are discussed in Sections 3.3 and 3.4. Bao, et al. Standards Track [Page 5] RFC 6052 IPv6 Addressing of IPv4/IPv6 Translators October 2010 Bits 64 to 71 of the address are reserved for compatibility with the host identifier format defined in the IPv6 addressing architecture [RFC4291]. These bits MUST be set to zero. When using a /96 Network-Specific Prefix, the administrators MUST ensure that the bits 64 to 71 are set to zero. A simple way to achieve that is to construct the /96 Network-Specific Prefix by picking a /64 prefix, and then adding 4 octets set to zero. The IPv4 address is encoded following the prefix, most significant bits first. Depending of the prefix length, the 4 octets of the address may be separated by the reserved octet "u", whose 8 bits MUST be set to zero. In particular: o When the prefix is 32 bits long, the IPv4 address is encoded in positions 32 to 63. o When the prefix is 40 bits long, 24 bits of the IPv4 address are encoded in positions 40 to 63, with the remaining 8 bits in position 72 to 79. o When the prefix is 48 bits long, 16 bits of the IPv4 address are encoded in positions 48 to 63, with the remaining 16 bits in position 72 to 87. o When the prefix is 56 bits long, 8 bits of the IPv4 address are encoded in positions 56 to 63, with the remaining 24 bits in position 72 to 95. o When the prefix is 64 bits long, the IPv4 address is encoded in positions 72 to 103. o When the prefix is 96 bits long, the IPv4 address is encoded in positions 96 to 127. There are no remaining bits, and thus no suffix, if the prefix is 96 bits long. In the other cases, the remaining bits of the address constitute the suffix. These bits are reserved for future extensions and SHOULD be set to zero. Address translators who receive IPv4- embedded IPv6 addresses where these bits are not zero SHOULD ignore the bits' value and proceed as if the bits' value were zero. (Future extensions may specify a different behavior.) Bao, et al. Standards Track [Page 6] RFC 6052 IPv6 Addressing of IPv4/IPv6 Translators October 2010 2.3. Address Translation Algorithms IPv4-embedded IPv6 addresses are composed according to the following algorithm: o Concatenate the prefix, the 32 bits of the IPv4 address, and the suffix (if needed) to obtain a 128-bit address. o If the prefix length is less than 96 bits, insert the null octet "u" at the appropriate position (bits 64 to 71), thus causing the least significant octet to be excluded, as documented in Figure 1. The IPv4 addresses are extracted from the IPv4-embedded IPv6 addresses according to the following algorithm: o If the prefix is 96 bits long, extract the last 32 bits of the IPv6 address; o For the other prefix lengths, remove the "u" octet to obtain a 120-bit sequence (effectively shifting bits 72-127 to positions 64-119), then extract the 32 bits following the prefix. 2.4. Text Representation IPv4-embedded IPv6 addresses will be represented in text in conformity with Section 2.2 of [RFC4291]. IPv4-embedded IPv6 addresses constructed using the Well-Known Prefix or a /96 Network- Specific Prefix may be represented using the alternative form presented in Section 2.2 of [RFC4291], with the embedded IPv4 address represented in dotted decimal notation. Examples of such representations are presented in Tables 1 and 2. +-----------------------+------------+------------------------------+ | Network-Specific | IPv4 | IPv4-embedded IPv6 address | | Prefix | address | | +-----------------------+------------+------------------------------+ | 2001:db8::/32 | 192.0.2.33 | 2001:db8:c000:221:: | | 2001:db8:100::/40 | 192.0.2.33 | 2001:db8:1c0:2:21:: | | 2001:db8:122::/48 | 192.0.2.33 | 2001:db8:122:c000:2:2100:: | | 2001:db8:122:300::/56 | 192.0.2.33 | 2001:db8:122:3c0:0:221:: | | 2001:db8:122:344::/64 | 192.0.2.33 | 2001:db8:122:344:c0:2:2100:: | | 2001:db8:122:344::/96 | 192.0.2.33 | 2001:db8:122:344::192.0.2.33 | +-----------------------+------------+------------------------------+ Table 1: Text Representation of IPv4-Embedded IPv6 Addresses Using Network-Specific Prefixes Bao, et al. Standards Track [Page 7] RFC 6052 IPv6 Addressing of IPv4/IPv6 Translators October 2010 +-------------------+--------------+----------------------------+ | Well-Known Prefix | IPv4 address | IPv4-Embedded IPv6 address | +-------------------+--------------+----------------------------+ | 64:ff9b::/96 | 192.0.2.33 | 64:ff9b::192.0.2.33 | +-------------------+--------------+----------------------------+ Table 2: Text Representation of IPv4-Embedded IPv6 Addresses Using the Well-Known Prefix The Network-Specific Prefix examples in Table 1 are derived from the IPv6 prefix reserved for documentation in [RFC3849]. The IPv4 address 192.0.2.33 is part of the subnet 192.0.2.0/24 reserved for documentation in [RFC5735]. The representation of IPv6 addresses is compatible with [RFC5952]. 3. Deployment Guidelines 3.1. Restrictions on the Use of the Well-Known Prefix The Well-Known Prefix MUST NOT be used to represent non-global IPv4 addresses, such as those defined in [RFC1918] or listed in Section 3 of [RFC5735]. Address translators MUST NOT translate packets in which an address is composed of the Well-Known Prefix and a non- global IPv4 address; they MUST drop these packets. The Well-Known Prefix SHOULD NOT be used to construct IPv4- translatable IPv6 addresses. The nodes served by IPv4-translatable IPv6 addresses should be able to receive global IPv6 traffic bound to their IPv4-translatable IPv6 address without incurring intermediate protocol translation. This is only possible if the specific prefix used to build the IPv4-translatable IPv6 addresses is advertised in inter-domain routing, but the advertisement of more specific prefixes derived from the Well-Known Prefix is not supported, as explained in Section 3.2. Network-Specific Prefixes SHOULD be used in these scenarios, as explained in Section 3.3. The Well-Known Prefix MAY be used by organizations deploying translation services, as explained in Section 3.4. 3.2. Impact on Inter-Domain Routing The Well-Known Prefix MAY appear in inter-domain routing tables, if service providers decide to provide IPv6-IPv4 interconnection services to peers. Advertisement of the Well-Known Prefix SHOULD be controlled either by upstream and/or downstream service providers according to inter-domain routing policies, e.g., through Bao, et al. Standards Track [Page 8] RFC 6052 IPv6 Addressing of IPv4/IPv6 Translators October 2010 configuration of BGP [RFC4271]. Organizations that advertise the Well-Known Prefix in inter-domain routing MUST be able to provide IPv4/IPv6 translation service. When the IPv4/IPv6 translation relies on the Well-Known Prefix, IPv4- embedded IPv6 prefixes longer than the Well-Known Prefix MUST NOT be advertised in BGP (especially External BGP) [RFC4271] because this leads to importing the IPv4 routing table into the IPv6 one and therefore introduces scalability issues to the global IPv6 routing table. Administrators of BGP nodes SHOULD configure filters that discard advertisements of embedded IPv6 prefixes longer than the Well-Known Prefix. When the IPv4/IPv6 translation service relies on Network-Specific Prefixes, the IPv4-translatable IPv6 prefixes used in stateless translation MUST be advertised with proper aggregation to the IPv6 Internet. Similarly, if translators are configured with multiple Network-Specific Prefixes, these prefixes MUST be advertised to the IPv6 Internet with proper aggregation. 3.3. Choice of Prefix for Stateless Translation Deployments Organizations may deploy translation services using stateless translation. In these deployments, internal IPv6 nodes are addressed using IPv4-translatable IPv6 addresses, which enable them to be accessed by IPv4 nodes. The addresses of these external IPv4 nodes are then represented in IPv4-converted IPv6 addresses. Organizations deploying stateless IPv4/IPv6 translation SHOULD assign a Network-Specific Prefix to their IPv4/IPv6 translation service. IPv4-translatable and IPv4-converted IPv6 addresses MUST be constructed as specified in Section 2.2. IPv4-translatable IPv6 addresses MUST use the selected Network-Specific Prefix. Both IPv4- translatable IPv6 addresses and IPv4-converted IPv6 addresses SHOULD use the same prefix. Using the same prefix ensures that IPv6 nodes internal to the organization will use the most efficient paths to reach the nodes served by IPv4-translatable IPv6 addresses. Specifically, if a node learns the IPv4 address of a target internal node without knowing that this target is in fact located behind the same translator that the node also uses, translation rules will ensure that the IPv6 address constructed with the Network-Specific Prefix is the same as the IPv4-translatable IPv6 address assigned to the target. Standard routing preference (i.e., "most specific match wins") will then ensure that the IPv6 packets are delivered directly, without requiring that translators receive the packets and then return them in the direction from which they came. Bao, et al. Standards Track [Page 9] RFC 6052 IPv6 Addressing of IPv4/IPv6 Translators October 2010 The intra-domain routing protocol must be able to deliver packets to the nodes served by IPv4-translatable IPv6 addresses. This may require routing on some or all of the embedded IPv4 address bits. Security considerations detailed in Section 5 require that routers check the validity of the IPv4-translatable IPv6 source addresses, using some form of reverse path check. The management of stateless address translation can be illustrated with a small example: We will consider an IPv6 network with the prefix 2001:db8: 122::/48. The network administrator has selected the Network- Specific Prefix 2001:db8:122:344::/64 for managing stateless IPv4/ IPv6 translation. The IPv4-translatable address block for IPv4 subnet 192.0.2.0/24 is 2001:db8:122:344:c0:2::/96. In this network, the host A is assigned the IPv4-translatable IPv6 address 2001:db8:122:344:c0:2:2100::, which corresponds to the IPv4 address 192.0.2.33. Host A's address is configured either manually or through DHCPv6. In this example, host A is not directly connected to the translator, but instead to a link managed by a router R. The router R is configured to forward to A the packets bound to 2001: db8:122:344:c0:2:2100::. To receive these packets, R will advertise reachability of the prefix 2001:db8:122:344:c0:2:2100::/ 104 in the intra-domain routing protocol -- or perhaps a shorter prefix if many hosts on link have IPv4-translatable IPv6 addresses derived from the same IPv4 subnet. If a packet bound to 192.0.2.33 reaches the translator, the destination address will be translated to 2001:db8:122:344:c0:2:2100::, and the packet will be routed towards R and then to A. Let's suppose now that a host B of the same domain learns the IPv4 address of A, maybe through an application-specific referral. If B has translation-aware software, B can compose a destination address by combining the Network-Specific Prefix 2001:db8:122: 344::/64 and the IPv4 address 192.0.2.33, resulting in the address 2001:db8:122:344:c0:2:2100::. The packet sent by B will be forwarded towards R, and then to A, avoiding protocol translation. Forwarding, and reverse path checks, are more efficient when performed on the combination of the prefix and the IPv4 address. In theory, routers are able to route on prefixes of any length, but in practice there may be routers for which routing on prefixes larger than 64 bits is slower. However, routing efficiency is not the only consideration in the choice of a prefix length. Organizations also need to consider the availability of prefixes, and the potential impact of all-zero identifiers. Bao, et al. Standards Track [Page 10] RFC 6052 IPv6 Addressing of IPv4/IPv6 Translators October 2010 If a /32 prefix is used, all the routing bits are contained in the top 64 bits of the IPv6 address, leading to excellent routing properties. These prefixes may however be hard to obtain, and allocation of a /32 to a small set of IPv4-translatable IPv6 addresses may be seen as wasteful. In addition, the /32 prefix and a zero suffix lead to an all-zero interface identifier, which is an issue that we discuss in Section 4.1. Intermediate prefix lengths such as /40, /48, or /56 appear as compromises. Only some of the IPv4 bits are part of the /64 prefixes. Reverse path checks, in particular, may have a limited efficiency. Reverse path checks limited to the most significant bits of the IPv4 address will reduce the possibility of spoofing external IPv4 addresses, but would allow IPv6 nodes to spoof internal IPv4- translatable IPv6 addresses. We propose a compromise, based on using no more than 1/256th of an organization's allocation of IPv6 addresses for the IPv4/IPv6 translation service. For example, if the organization is an Internet Service Provider with an allocated IPv6 prefix /32 or shorter, the ISP could dedicate a /40 prefix to the translation service. An end site with a /48 allocation could dedicate a /56 prefix to the translation service, or possibly a /96 prefix if all IPv4- translatable IPv6 addresses are located on the same link. The recommended prefix length is also a function of the deployment scenario. The stateless translation can be used for Scenario 1, Scenario 2, Scenario 5, and Scenario 6 defined in [v4v6-FRAMEWORK]. For different scenarios, the prefix length recommendations are: o For Scenario 1 (an IPv6 network to the IPv4 Internet) and Scenario 2 (the IPv4 Internet to an IPv6 network), an ISP holding a /32 allocation SHOULD use a /40 prefix, and a site holding a /48 allocation SHOULD use a /56 prefix. o For Scenario 5 (an IPv6 network to an IPv4 network) and Scenario 6 (an IPv4 network to an IPv6 network), the deployment SHOULD use a /64 or a /96 prefix. 3.4. Choice of Prefix for Stateful Translation Deployments Organizations may deploy translation services based on stateful translation technology. An organization may decide to use either a Network-Specific Prefix or the Well-Known Prefix for its stateful IPv4/IPv6 translation service. Bao, et al. Standards Track [Page 11] RFC 6052 IPv6 Addressing of IPv4/IPv6 Translators October 2010 When these services are used, IPv6 nodes are addressed through standard IPv6 addresses, while IPv4 nodes are represented by IPv4- converted IPv6 addresses, as specified in Section 2.2. The stateful nature of the translation creates a potential stability issue when the organization deploys multiple translators. If several translators use the same prefix, there is a risk that packets belonging to the same connection may be routed to different translators as the internal routing state changes. This issue can be avoided either by assigning different prefixes to different translators or by ensuring that all translators using the same prefix coordinate their state. Stateful translation can be used in scenarios defined in [v4v6-FRAMEWORK]. The Well-Known Prefix SHOULD be used in these scenarios, with two exceptions: o In all scenarios, the translation MAY use a Network-Specific Prefix, if deemed appropriate for management reasons. o The Well-Known Prefix MUST NOT be used for Scenario 3 (the IPv6 Internet to an IPv4 network), as this would lead to using the Well-Known Prefix with non-global IPv4 addresses. That means a Network-Specific Prefix (for example, a /96 prefix) MUST be used in that scenario. 4. Design Choices The prefix that we have chosen reflects two design choices, the null suffix and the specific value of the Well-Known Prefix. We provide here a summary of the discussions leading to those two choices. 4.1. Choice of Suffix The address format described in Section 2.2 recommends a zero suffix. Before making this recommendation, we considered different options: checksum neutrality, the encoding of a port range, and a value different than 0. In the case of stateless translation, there would be no need for the translator to recompute a one's complement checksum if both the IPv4- translatable and the IPv4-converted IPv6 addresses were constructed in a "checksum-neutral" manner, that is, if the IPv6 addresses would have the same one's complement checksum as the embedded IPv4 address. In the case of stateful translation, checksum neutrality does not eliminate checksum computation during translation, as only one of the two addresses would be checksum neutral. We considered reserving 16 bits in the suffix to guarantee checksum neutrality, but declined Bao, et al. Standards Track [Page 12] RFC 6052 IPv6 Addressing of IPv4/IPv6 Translators October 2010 because it would not help with stateful translation and because checksum neutrality can also be achieved by an appropriate choice of the Network-Specific Prefix, i.e., selecting a prefix whose one's complement checksum equals either 0 or 0xffff. There have been proposals to complement stateless translation with a port-range feature. Instead of mapping an IPv4 address to exactly one IPv6 prefix, the options would allow several IPv6 nodes to share an IPv4 address, with each node managing a different range of ports. If a port range extension is needed, it could be defined later, using bits currently reserved as null in the suffix. When a /32 prefix is used, an all-zero suffix results in an all-zero interface identifier. We understand the conflict with Section 2.6.1 of RFC4291, which specifies that all zeroes are used for the subnet- router anycast address. However, in our specification, there is only one node with an IPv4-translatable IPv6 address in the /64 subnet, so the anycast semantic does not create confusion. We thus decided to keep the null suffix for now. This issue does not exist for prefixes larger than 32 bits, such as the /40, /56, /64, and /96 prefixes that we recommend in Section 3.3. 4.2. Choice of the Well-Known Prefix Before making our recommendation of the Well-Known Prefix, we were faced with three choices: o reuse the IPv4-mapped prefix, ::ffff:0:0/96, as specified in RFC 2765, Section 2.1; o request IANA to allocate a /32 prefix, or o request allocation of a new /96 prefix. We weighted the pros and cons of these choices before settling on the recommended /96 Well-Known Prefix. The main advantage of the existing IPv4-mapped prefix is that it is already defined. Reusing that prefix would require minimal standardization efforts. However, being already defined is not just an advantage, as there may be side effects of current implementations. When presented with the IPv4-mapped prefix, current versions of Windows and Mac OS generate IPv4 packets, but will not send IPv6 packets. If we used the IPv4-mapped prefix, these nodes would not be able to support translation without modification. This will defeat the main purpose of the translation techniques. We thus eliminated the first choice, i.e., decided to not reuse the IPv4- mapped prefix, ::ffff:0:0/96. Bao, et al. Standards Track [Page 13] RFC 6052 IPv6 Addressing of IPv4/IPv6 Translators October 2010 A /32 prefix would have allowed the embedded IPv4 address to fit within the top 64 bits of the IPv6 address. This would have facilitated routing and load balancing when an organization deploys several translators. However, such destination-address-based load balancing may not be desirable. It is not compatible with Session Traversal Utilities for NAT (STUN) [RFC5389] in the deployments involving multiple stateful translators, each one having a different pool of IPv4 addresses. STUN compatibility would only be achieved if the translators managed the same pool of IPv4 addresses and were able to coordinate their translation state, in which case there is no big advantage to using a /32 prefix rather than a /96 prefix. According to Section 2.2 of [RFC4291], in the legal textual representations of IPv6 addresses, dotted decimal can only appear at the end. The /96 prefix is compatible with that requirement. It enables the dotted decimal notation without requiring an update to [RFC4291]. This representation makes the address format easier to use and the log files easier to read. The prefix that we recommend has the particularity of being "checksum neutral". The sum of the hexadecimal numbers "0064" and "ff9b" is "ffff", i.e., a value equal to zero in one's complement arithmetic. An IPv4-embedded IPv6 address constructed with this prefix will have the same one's complement checksum as the embedded IPv4 address. 5. Security Considerations 5.1. Protection against Spoofing IPv4/IPv6 translators can be modeled as special routers, are subject to the same risks, and can implement the same mitigations. (The discussion of generic threats to routers and their mitigations is beyond the scope of this document.) There is, however, a particular risk that directly derives from the practice of embedding IPv4 addresses in IPv6: address spoofing. An attacker could use an IPv4-embedded IPv6 address as the source address of malicious packets. After translation, the packets will appear as IPv4 packets from the specified source, and the attacker may be hard to track. If left without mitigation, the attack would allow malicious IPv6 nodes to spoof arbitrary IPv4 addresses. The mitigation is to implement reverse path checks and to verify throughout the network that packets are coming from an authorized location. Bao, et al. Standards Track [Page 14] RFC 6052 IPv6 Addressing of IPv4/IPv6 Translators October 2010 5.2. Secure Configuration The prefixes used for address translation are used by IPv6 nodes to send packets to IPv6/IPv4 translators. Attackers could attempt to fool nodes, DNS gateways, and IPv4/IPv6 translators into using wrong values for these parameters, resulting in network disruption, denial of service, and possible information disclosure. To mitigate such attacks, network administrators need to ensure that prefixes are configured in a secure way. The mechanisms for achieving secure configuration of prefixes are beyond the scope of this document. 5.3. Firewall Configuration Many firewalls and other security devices filter traffic based on IPv4 addresses. Attackers could attempt to fool these firewalls by sending IPv6 packets to or from IPv6 addresses that translate to the filtered IPv4 addresses. If the attack is successful, traffic that was previously blocked might be able to pass through the firewalls disguised as IPv6 packets. In all such scenarios, administrators should assure that packets that send to or from IPv4-embedded IPv6 addresses are subject to the same filtering as those directly sent to or from the embedded IPv4 addresses. The mechanisms for configuring firewalls and security devices to achieve this filtering are beyond the scope of this document. 6. IANA Considerations IANA has made the following changes in the "Internet Protocol Version 6 Address Space" registry located at http://www.iana.org. OLD: IPv6 Prefix Allocation Reference Note ----------- ---------------- ------------ ---------------- 0000::/8 Reserved by IETF [RFC4291] [1][5] NEW: IPv6 Prefix Allocation Reference Note ----------- ---------------- ------------ ---------------- 0000::/8 Reserved by IETF [RFC4291] [1][5][6] [6] The "Well-Known Prefix" 64:ff9b::/96 used in an algorithmic mapping between IPv4 to IPv6 addresses is defined out of the 0000::/8 address block, per RFC 6052. Bao, et al. Standards Track [Page 15] RFC 6052 IPv6 Addressing of IPv4/IPv6 Translators October 2010 7. Acknowledgements Many people in the BEHAVE WG have contributed to the discussion that led to this document, including Andrew Sullivan, Andrew Yourtchenko, Ari Keranen, Brian Carpenter, Charlie Kaufman, Dan Wing, Dave Thaler, David Harrington, Ed Jankiewicz, Fred Baker, Hiroshi Miyata, Iljitsch van Beijnum, John Schnizlein, Keith Moore, Kevin Yin, Magnus Westerlund, Margaret Wasserman, Masahito Endo, Phil Roberts, Philip Matthews, Remi Denis-Courmont, Remi Despres, and William Waites. Marcelo Bagnulo is partly funded by Trilogy, a research project supported by the European Commission under its Seventh Framework Program. 8. Contributors The following individuals co-authored documents from which text has been incorporated, and are listed in alphabetical order. Dave Thaler Microsoft Corporation One Microsoft Way Redmond, WA 98052 USA Phone: +1 425 703 8835 EMail: dthaler@microsoft.com Fred Baker Cisco Systems Santa Barbara, California 93117 USA Phone: +1-408-526-4257 Fax: +1-413-473-2403 EMail: fred@cisco.com Hiroshi Miyata Yokogawa Electric Corporation 2-9-32 Nakacho Musashino-shi, Tokyo 180-8750 JAPAN EMail: h.miyata@jp.yokogawa.com Bao, et al. Standards Track [Page 16] RFC 6052 IPv6 Addressing of IPv4/IPv6 Translators October 2010 9. References 9.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing Architecture", RFC 4291, February 2006. 9.2. Informative References [DNS64] Bagnulo, M., Sullivan, A., Matthews, P., and I. Beijnum, "DNS64: DNS extensions for Network Address Translation from IPv6 Clients to IPv4 Servers", Work in Progress, October 2010. [RFC1918] Rekhter, Y., Moskowitz, R., Karrenberg, D., Groot, G., and E. Lear, "Address Allocation for Private Internets", BCP 5, RFC 1918, February 1996. [RFC3484] Draves, R., "Default Address Selection for Internet Protocol version 6 (IPv6)", RFC 3484, February 2003. [RFC3849] Huston, G., Lord, A., and P. Smith, "IPv6 Address Prefix Reserved for Documentation", RFC 3849, July 2004. [RFC4271] Rekhter, Y., Li, T., and S. Hares, "A Border Gateway Protocol 4 (BGP-4)", RFC 4271, January 2006. [RFC5389] Rosenberg, J., Mahy, R., Matthews, P., and D. Wing, "Session Traversal Utilities for NAT (STUN)", RFC 5389, October 2008. [RFC5735] Cotton, M. and L. Vegoda, "Special Use IPv4 Addresses", BCP 153, RFC 5735, January 2010. [RFC5952] Kawamura, S. and M. Kawashima, "A Recommendation for IPv6 Address Text Representation", RFC 5952, August 2010. [v4v6-FRAMEWORK] Baker, F., Li, X., Bao, C., and K. Yin, "Framework for IPv4/IPv6 Translation", Work in Progress, August 2010. Bao, et al. Standards Track [Page 17] RFC 6052 IPv6 Addressing of IPv4/IPv6 Translators October 2010 Authors' Addresses Congxiao Bao CERNET Center/Tsinghua University Room 225, Main Building, Tsinghua University Beijing, 100084 China Phone: +86 10-62785983 EMail: congxiao@cernet.edu.cn Christian Huitema Microsoft Corporation One Microsoft Way Redmond, WA 98052-6399 U.S.A. EMail: huitema@microsoft.com Marcelo Bagnulo UC3M Av. Universidad 30 Leganes, Madrid 28911 Spain Phone: +34-91-6249500 EMail: marcelo@it.uc3m.es URI: http://www.it.uc3m.es/marcelo Mohamed Boucadair France Telecom 3, Av Francois Chateaux Rennes 350000 France EMail: mohamed.boucadair@orange-ftgroup.com Xing Li CERNET Center/Tsinghua University Room 225, Main Building, Tsinghua University Beijing, 100084 China Phone: +86 10-62785983 EMail: xing@cernet.edu.cn Bao, et al. Standards Track [Page 18] </pre>

IPv6 Addressing of IPv4/IPv6 Translators

Internet Engineering Task Force (IETF) C. Bao Request for Comments: 6052 CERNET Center/Tsinghua U...

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A Model of IPv6 IPv4 Dual Stack Internet Access Service

<pre>Network Working Group Y. Shirasaki Request for Comments: 4241 S. Miyakawa Category: Informational T. Yamasaki NTT Communications A. Takenouchi NTT December 2005 A Model of IPv6/IPv4 Dual Stack Internet Access Service Status of This Memo This memo provides information for the Internet community. It does not specify an Internet standard of any kind. Distribution of this memo is unlimited. Copyright Notice Copyright (C) The Internet Society (2005). IESG Note This RFC is not a candidate for any level of Internet Standard. The IETF disclaims any knowledge of the fitness of this RFC for any purpose and notes that the decision to publish is not based on IETF review apart from IESG review for conflict with IETF work. The RFC Editor has chosen to publish this document at its discretion. See RFC 3932 for more information. Abstract This memo is a digest of the user network interface specification of NTT Communications' dual stack ADSL access service, which provide a IPv6/IPv4 dual stack services to home users. In order to simplify user setup, these services have a mechanism to configure IPv6 specific parameters automatically. The memo focuses on two basic parameters: the prefix assigned to the user and the addresses of IPv6 DNS servers, and it specifies a way to deliver these parameters to Customer Premises Equipment (CPE) automatically. Shirasaki, et al. Informational [Page 1] RFC 4241 Dual Stack Access Service December 2005 1. Introduction This memo is a digest of the user network interface specification of NTT Communications' dual stack ADSL access service, which provide IPv6/IPv4 dual stack services to home users. In order to simplify user setup, these services have a mechanism to configure IPv6 specific parameters automatically. The memo focuses on two basic parameters: the prefix assigned to the user and the addresses of IPv6 DNS servers, and it specifies a way to deliver these parameters to Customer Premises Equipment (CPE) automatically. This memo covers two topics: an architecture for IPv6/IPv4 dual stack access service and an automatic configuration function for IPv6- specific parameters. The architecture is mainly targeted at a leased-line ADSL service for home users. It assumes that there is a Point-to-Point Protocol (PPP) logical link between Customer Premises Equipment (CPE) and Provider Edge (PE) equipment. In order to exclude factors that are specific to access lines, this architecture only specifies PPP and its upper layers. To satisfy [RFC3177], the prefix length that is delegated to the CPE is /48, but /64 is also a possible option. In this architecture, IPv6/IPv4 dual stack service is specified as follows. o IPv6 and IPv4 connectivities are provided over a single PPP logical link. o IPv6 connectivity is independent of IPv4 connectivity. IPV6CP and IPCP work independently over a single PPP logical link. Figure 1 shows an outline of the service architecture. NTT Communications has been providing a commercial service based on this architecture since the Summer 2002. | _____________ [HOST]-+ +-----------+ +----------+ / \ | | Customer | ADSL line | Provider | | ISP core and | +-+ Premises +---------------+ Edge |--| The internet | | | Equipment | to subscriber +-----+----+ \_____________/ [HOST]-+ +-----------+ | | | | +-----+------+ | +-+----------+ | AAA server | | | DNS server | +------------+ | +------------+ +-+--------------+ | NTP server etc.| Figure 1: Dual Stack Access Service Architecture +----------------+ Shirasaki, et al. Informational [Page 2] RFC 4241 Dual Stack Access Service December 2005 The automatic configuration function aims at simplification of user setup. Usually, users have to configure at least two IPv6-specific parameters: prefix(es) assigned to them [RFC3769] and IPv6 DNS servers' addresses. The function is composed of two sub-functions: o Delegation of prefix(es) to be used in the user site. o Notification of IPv6 DNS server addresses and/or other server addresses. Section 2 of this memo details the user/network interface. Section 3 describes an example connection sequence. 2. User/Network Interface This section describes details of the user/network interface specification. Only PPP over Ethernet (PPPoE) and its upper layers are mentioned; the other layers, such as Ethernet and lower layers, are out of scope. IPv4-related parameter configuration is also out of scope. 2.1. Below the IP Layer The service uses PPP connection and Challenge Handshake Authentication Protocol (CHAP) authentication to identify each CPE. The CPE and PE handle both the PPP Internet Protocol Control Protocol (IPCP) [RFC1332] and the Internet Protocol V6 Control Protocol (IPV6CP) [RFC2472] identically and simultaneously over a single PPP connection. This means either the CPE or the PE can open/close any Network Control Protocol (NCP) session at any time without any side- effect for the other. It is intended that users can choose among three services: IPv4 only, IPv6 only, and IPv4/IPv6 dual stack. A CPE connected to an ADSL line discovers a PE with the PPPoE mechanism [RFC2516]. Note that, because CPE and PE can negotiate only their interface identifiers with IPV6CP, PE and CPE can use only link-local-scope addresses before the prefix delegation mechanism described below is run. 2.2. IP Layer After IPV6CP negotiation, the CPE initiates a prefix delegation request. The PE chooses a global-scope prefix for the CPE with information from an Authentication, Authorization, and Accounting (AAA) server or local prefix pools, and it delegates the prefix to the CPE. Once the prefix is delegated, the prefix is subnetted and assigned to the local interfaces of the CPE. The CPE begins sending Shirasaki, et al. Informational [Page 3] RFC 4241 Dual Stack Access Service December 2005 router advertisements for the prefixes on each link. Eventually, hosts can acquire global-scope prefixes through conventional IPv6 stateless [RFC2462] or stateful auto-configuration mechanisms ([RFC3315], etc.) and begin to communicate using global-scope addresses. 2.3. Prefix Delegation The PE delegates prefixes to CPE using Dynamic Host Configuration Protocol for IPv6 (DHCPv6) [RFC3315] with the prefix delegation options [RFC3633]. The sequence for prefix delegation is as follows: o The CPE requests prefix(es) from a PE by sending a DHCPv6 Solicit message that has a link-local source address negotiated by IPV6CP, mentioned in the previous section, and includes an IA_PD option. o An AAA server provides prefix(es) to the PE or the PE chooses prefix(es) from its local pool, and the PE returns an Advertise message that contains an IA_PD option and IA_PD Prefix options. The prefix-length in the IA_PD Prefix option is 48. IA_PD option and IA_PD Prefix options for the chosen prefix(es) back to the PE. o The PE confirms the prefix(es) in the Request message in a Reply message. If IPV6CP is terminated or restarted by any reason, CPE must initiate a Rebind/Reply message exchange as described in [RFC3633]. 2.4. Address Assignment The CPE assigns global-scope /64 prefixes, subnetted from the delegated prefix, to its downstream interfaces. When the delegated prefix has an infinite lifetime, the preferred and valid lifetimes of assigned /64 prefixes should be the default values in [RFC2461]. Because a link-local address is already assigned to the CPE's upstream interface, global-scope address assignment for that interface is optional. 2.5. Routing The CPE and PE use static routing between them, and no routing protocol traffic is necessary. Shirasaki, et al. Informational [Page 4] RFC 4241 Dual Stack Access Service December 2005 The CPE configures its PPPoE logical interface or the link-local address of PE as the IPv6 default gateway, automatically after the prefix delegation exchange. When the CPE receives packets that are destined for the addresses in the delegated /48 prefix, the CPE must not forward the packets to a PE. The CPE should return ICMPv6 Destination Unreachable message to a source address or silently discard the packets, when the original packet is destined for the unassigned prefix in the delegated prefix. (For example, the CPE should install a reject route or null interface as next hop for the delegated prefix.) 2.6. Obtaining Addresses of DNS Servers The service provides IPv6 recursive DNS servers in the ISP site. The PE notifies the global unicast addresses of these servers with the Domain Name Server option that is described in [RFC3646], in Advertise/Reply messages on the prefix delegation message exchange. Devices connected to user network may learn a recursive DNS server address with the mechanism described in [RFC3736]. The CPE may serve as a local DNS proxy server and include its address in the DNS server address list. This is easy to implement, because it is analogous to IPv4 SOHO router (192.168.0.1 is a DNS proxy server and a default router in most sites). 2.7. Miscellaneous Information The PE may notify other IPv6-enabled server addresses, such as Network Time Protocol servers [RFC4075], SIP servers [RFC3319], etc., in an Advertise/Reply message on the prefix delegation message exchange, if those are available. 2.8. Connectivity Monitoring ICMPv6 Echo Request will be sent to the user network for connectivity monitoring in the service. The CPE must return a single IPv6 Echo Reply packet when it receives an ICMPv6 Echo Request packet. The health-check packets are addressed to a subnet-router anycast address for the delegated prefix. The old document of APNIC IPv6 address assignment policy required that APNIC could ping the subnet anycast address to check address usage. Shirasaki, et al. Informational [Page 5] RFC 4241 Dual Stack Access Service December 2005 To achieve this requirement, for example, once the prefix 2001:db8:ffff::/48 is delegated, the CPE must reply to the ICMPv6 Echo Request destined for 2001:db8:ffff:: any time that IPV6CP and DHCPv6-PD are up for the upstream direction. Because some implementations couldn't reply when 2001:db8:ffff::/64 was assigned to its downstream physical interface and the interface was down, such an implementation should assign 2001:db8:ffff::/64 for the loopback interface, which is always up, and 2001:db8:ffff:1::/64, 2001:db8:ffff:2::/64, etc., to physical interfaces. 3. An Example of Connection Sequence CPE PE | | |----------PADI-------->| \ |<---------PADO---------| | PPPoE |----------PADR-------->| | Discovery Stage |<---------PADS---------| / | | |---Configure-Request-->| \ |<--Configure-Request---| | PPP Link Establishment Phase |<----Configure-Ack-----| | (LCP) |-----Configure-Ack---->| / | | |<------Challenge-------| \ |-------Response------->| | PPP Authentication Phase (CHAP) |<-------Success--------| / | | |---Configure-Request-->| \ |<--Configure-Request---| | |<----Configure-Nak-----| | PPP Network Layer Protocol Phase |<----Configure-Ack-----| | (IPCP) |---Configure-Request-->| | |<----Configure-Ack-----| / | | |---Configure-Request-->| \ |<--Configure-Request---| | PPP Network Layer Protocol Phase |<----Configure-Ack-----| | (IPV6CP) |-----Configure-Ack---->| / | | |--------Solicit------->| \ |<------Advertise-------| | DHCPv6 |--------Request------->| | |<--------Reply---------| / | | Figure 2: Example of Connection Sequence Shirasaki, et al. Informational [Page 6] RFC 4241 Dual Stack Access Service December 2005 Figure 2 is an example of a normal link-up sequence, from start of PPPoE to start of IPv6/IPv4 communications. IPv4 communication becomes available after IPCP negotiation. IPv6 communication with link-local scope addresses becomes possible after IPV6CP negotiation. IPv6 communication with global-scope addresses becomes possible after prefix delegation and conventional IPv6 address configuration mechanism. IPCP is independent of IPV6CP and prefix delegation. 4. Security Considerations In this architecture, the PE and CPE trust the point-to-point link between them; they trust that there is no man-in-the-middle and they trust PPPoE authentication. Because of this, DHCP authentication is not considered necessary and is not used. The service provides an always-on global-scope prefix for users. Each device connected to user network has global-scope addresses. Without any packet filters, devices might be accessible from outside the user network in that case. The CPE and each device involved in the service should have functionality to protect against unauthorized accesses, such as a stateful inspection packet filter. The relationship between CPE and devices connected to the user network for this problem should be considered in the future. 5. Acknowledgements Thanks are given for the input and review by Tatsuya Sato, Hideki Mouri, Koichiro Fujimoto, Hiroki Ishibashi, Ralph Droms, Ole Troan, Pekka Savola, and IPv6-ops-IAJapan members. 6. References 6.1. Normative References [RFC3177] IAB and IESG, "IAB/IESG Recommendations on IPv6 Address Allocations to Sites", RFC 3177, September 2001. [RFC1332] McGregor, G., "The PPP Internet Protocol Control Protocol (IPCP)", RFC 1332, May 1992. [RFC2472] Haskin, D. and E. Allen, "IP Version 6 over PPP", RFC 2472, December 1998. [RFC2516] Mamakos, L., Lidl, K., Evarts, J., Carrel, D., Simone, D., and R. Wheeler, "A Method for Transmitting PPP Over Ethernet (PPPoE)", RFC 2516, February 1999. Shirasaki, et al. Informational [Page 7] RFC 4241 Dual Stack Access Service December 2005 [RFC2462] Thomson, S. and T. Narten, "IPv6 Stateless Address Autoconfiguration", RFC 2462, December 1998. [RFC3315] Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C., and M. Carney, "Dynamic Host Configuration Protocol for IPv6 (DHCPv6)", RFC 3315, July 2003. [RFC3633] Troan, O. and R. Droms, "IPv6 Prefix Options for Dynamic Host Configuration Protocol (DHCP) version 6", RFC 3633, December 2003. RFC 3633, December 2003. [RFC2461] Narten, T., Nordmark, E. and W. Simpson, "Neighbor Discovery for IP Version 6 (IPv6)", RFC 2461, December 1998. [RFC3646] Droms, R., "DNS Configuration options for Dynamic Host Configuration Protocol for IPv6 (DHCPv6)", RFC 3646, December 2003. [RFC3736] Droms, R., "Stateless Dynamic Host Configuration Protocol (DHCP) Service for IPv6", RFC 3736, April 2004. [RFC4075] Kalusivalingam, V., "Simple Network Time Protocol (SNTP) Configuration Option for DHCPv6", RFC 4075, May 2005. [RFC3319] Schulzrinne, H. and B. Volz, "Dynamic Host Configuration Protocol (DHCPv6) Options for Session Initiation Protocol (SIP) Servers", RFC 3319, July 2003. 6.2. Informative References [RFC3769] Miyakawa, S. and R. Droms, "Requirements for IPv6 Prefix Delegation", RFC 3769, June 2004. Shirasaki, et al. Informational [Page 8] RFC 4241 Dual Stack Access Service December 2005 Authors' Addresses Yasuhiro Shirasaki NTT Communications Corporation Tokyo Opera City Tower 21F 3-20-2 Nishi-Shinjuku, Shinjuku-ku Tokyo 163-1421, Japan EMail: yasuhiro@nttv6.jp Shin Miyakawa, Ph. D NTT Communications Corporation Tokyo Opera City Tower 21F 3-20-2 Nishi-Shinjuku, Shinjuku-ku Tokyo 163-1421, Japan EMail: miyakawa@nttv6.jp Toshiyuki Yamasaki NTT Communications Corporation 1-1-6 Uchisaiwaicho, Chiyoda-ku Tokyo 100-8019, Japan EMail: t.yamasaki@ntt.com Ayako Takenouchi NTT Cyber Solutions Laboratories, NTT Corporation 3-9-11 Midori-Cho, Musashino-Shi Tokyo 180-8585, Japan EMail: takenouchi.ayako@lab.ntt.co.jp Shirasaki, et al. Informational [Page 9] RFC 4241 Dual Stack Access Service December 2005 Full Copyright Statement Copyright (C) The Internet Society (2005). This document is subject to the rights, licenses and restrictions contained in BCP 78 and at www.rfc-editor.org/copyright.html, and except as set forth therein, the authors retain all their rights. This document and the information contained herein are provided on an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. Intellectual Property The IETF takes no position regarding the validity or scope of any Intellectual Property Rights or other rights that might be claimed to pertain to the implementation or use of the technology described in this document or the extent to which any license under such rights might or might not be available; nor does it represent that it has made any independent effort to identify any such rights. Information on the procedures with respect to rights in RFC documents can be found in BCP 78 and BCP 79. Copies of IPR disclosures made to the IETF Secretariat and any assurances of licenses to be made available, or the result of an attempt made to obtain a general license or permission for the use of such proprietary rights by implementers or users of this specification can be obtained from the IETF on-line IPR repository at http://www.ietf.org/ipr. The IETF invites any interested party to bring to its attention any copyrights, patents or patent applications, or other proprietary rights that may cover technology that may be required to implement this standard. Please address the information to the IETF at ietf- ipr@ietf.org. Acknowledgement Funding for the RFC Editor function is currently provided by the Internet Society.</pre>

A Model of IPv6 IPv4 Dual Stack Internet Access Service

Network Working Group Y. Shirasaki Request for Comments: 4241 S. Miy...

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IPv6 Introduction

IP version 4 (IPv4) has been a core part of the TCP/IP protocol suite and has served well during tremendous growth of the Internet. IPv4, mostly called just IP, defines addressing and routing for most corporate networks that use TCP/IP as well as the public Internet. Though IPv4 has been a long-time companion, it has its shortcomings that created the need for a protocol that could replace IPv4. That protocol is Internet Protocol version 6 or IPv6 for short. IPv6 defines the same general functions that are defined by IPv4. However, there are differences in detail that we will explore in this chapter.<br /> IP version 6 (IPv6) serves as the protocol that will eventually replace IP version 4 (IPv4). The most obvious reason for migrating TCP/IP networks from IPv4 to IPv6 is growth. IPv4 uses a 32-bit address, which allows for a little over four billion addresses. It may seem like a pretty large number of addresses but the immense growth of networks and the Internet has almost exhausted our stock of available IPv4 addresses for new deployments. IPv6 uses 128-bit addresses and increases the number of available addresses to 2^128, a number so large that we don’t have a word for it.<br /> The change from IPv4 to IPv6 is not just about one protocol being replaced by another; it impacts many other protocols as well. In this super-sized chapter, we start by introducing IPv6 addressing and routing, also discussing troubleshooting of the same. We then cover OSPFv3 (Open Shortest Path First Version 3) and EIGRPv6 (Enhanced Interior Gateway Routing Protocol for IPv6), in detail.<b> </b><br /> <b>The IPv6 Protocols</b><br /> The core IPv6 protocol, defined in RFC 2460, describes the concept of a packet, addessing for those packets, and the role of hosts and routers. The end objective of IPv6 like IPv4 is to enable devices forward packets sourced by hosts through multiple routers so that they arrive at the correct destination. However, because IPv6 affects several other functions in a network as well beyond addressing and packet forwarding, many more RFCs must define other details. For example, some RFCs describe how to migrate from IPv4 to IPv6, while some other RFCs define newer versions of familiar IPv4 protocols for IPv6:<br /> <ul> <li><b>OSPF Version 3:</b> The older version 2 of OSPF works for IPv4 but not for IPv6. So, a newer version known as OSPF version 3 (OSPFv3) was created to support IPv6.</li> </ul> <ul> <li><b>EIGRP for IPv6:</b> EIGRP for IPv4 runs over IPv4 as the transport protocol, communicates only with IPv4 peers, and advertises only IPv4 routes. EIGRP for IPv6 follows the same model but it can propagate IPv6 prefixes to route IPv6 packets.<b> </b></li> </ul> <ul> <li><b>ICMP Version 6:</b> Internet Control Message Protocol (ICMP) worked well with IPv4 to provide feedback to senders on packet forwarding especially when packets could not be forwarded by a router. ICMP was changed into what is known as ICMP version 6 (ICMPv6) to support IPv6.<b> </b></li> </ul> <ul> <li><b>Neighbor Discovery Protocol:</b> Address Resolution Protocol (ARP) is used to discover the MAC addresses of hosts whose IPv4 addresses are known. IPv6 replaces ARP with the more general Neighbor Discovery Protocol (NDP).</li> </ul> IPv6 is a layer 3 routing protocol and defines a header that holds both the source and destination address fields, just like IPv4. The IPv6 header is <i>not</i> similar to the IPv4 header and the differences are more than just bigger source and destination addresses. The IPv6 header is bigger in size compared with the IPv4 header, though it is otherwise simpler for the sake of reducing the computational overhead on routers that process IPv6 packets. The following diagram displays the IPv6 header:<br /> <div align="center"> <b>Figure 14-1</b> IPv6 Header Format<b> </b></div> <b><img alt="14-1" class="aligncenter size-large wp-image-1187" height="699" src="http://www.freeccnastudyguide.com/wp-content/uploads/2014/05/14-1-1024x792.png" width="904" /></b><br /> <b>IPv6 Addressing</b><br /> There are three types of IP version 6 (IPv6) addresses:<br /> <ul> <li><b>Unicast:</b> A unicast address identifies a single interface and a packet sent to a unicast address is delivered to the one interface identified by that address.</li> </ul> <ul> <li><b>Anycast:</b> An anycast address is for a set of interfaces typically on different nodes. A packet sent to an anycast address is delivered to only one of the interfaces identified by that address. The <i>nearest</i> interface, according to the routing protocol metric, gets the packet delivered to it.<b> </b></li> </ul> <ul> <li><b>Multicast:</b> A multicast address identifies a set of interfaces typically on different nodes just like an anycast address. However, a packet sent to a multicast address is delivered to <i>all</i> interfaces identified by that address.</li> </ul> If you are wondering what happened to broadcast addresses, they don’t exist in the IPv6 world. Multicast addresses also function in place of broadcast addresses.<br /> <div class="stb-info_box" id="stb-box-618"> <b>Key Concept </b>IPv6 broadcast addresses are a special case of multicast addresses.</div> Just like IPv4, IPv6 addresses of all types are assigned to interfaces, not nodes. The IPv6 unicast address of any of a node’s interfaces can be used as an identifier for that node.<br /> A single interface may have multiple IPv6 addresses of any type (unicast, anycast, and multicast) and scope.<b> </b><br /> <b>Representation of IPv6 Addresses and Prefixes</b><br /> An IP version 6 address is a 128-bit value written as xxxx:xxxx:xxxx:xxxx:xxxx:xxxx:xxxx:xxxx where each <i>x</i> is a hexadecimal digit. There are 8 groups of 4 hexadecimal digits in the above representation, with each digit representing four binary digits (bits). It is not necessary to write the leading zeros in an individual group of four hex digits.<br /> An example of an IPv6 address is:<br /> <div class="stb-grey_box" id="stb-box-1270"> 2001:0DB8:0000:0000:0006:0600:300D:527B </div> The same IPv6 address can also be written as:<br /> <div class="stb-grey_box" id="stb-box-6230">      2001:DB8:0:0:6:600:300D:527B</div> There must be at least one digit in every group of four digits. That is the reason, the groups with all four zeros in the mentioned address are replaced with a single zero.<br /> In order to make writing IPv6 addresses with long strings of zero bits easier, a method is available to compress zeros. The special symbol <b>::</b> can be used to represent one or more adjacent groups of 16 bits of zeros. The symbol <b>::</b> can appear only once in an address though. The <b>::</b> can also include leading zeros after the last group of 16 zero bits, or before the first group of 16 zero bits. For example, the same address we mentioned can be squeezed further as:<br /> <div class="stb-grey_box" id="stb-box-1765"> 2001:DB8<b>::</b>6:600:300D:527B</div> Note that the <b>::</b> in above representation replaces two groups of 16 zero bits, as well as three leading zeros in the group after those two groups of 16 zero bits.<br /> The table below first shows the full representation of a few IPv6 addresses, and then shows the short representation making use of the <b>::</b> according to rules we described.<br /> <div align="center"> <b>Table 13-1</b> IPv6 Addresses Representation</div> <div align="center"> <table border="1" cellpadding="0" cellspacing="0" style="width: 504px;"><tbody> <tr><td width="288"><b>Full Representation</b></td><td width="216"><b>Short Representation</b></td></tr> <tr><td width="288">2001:0DB8:0000:85A4:0000:08B3:0370:7348</td><td width="216">2001:DB8:0:85A4<b>::</b>8B3:370:7348</td></tr> <tr><td width="288">FF01:0000:0000:0000:0000:0000:0000:0212</td><td width="216">FF01<b>::</b>212</td></tr> <tr><td width="288">0000:0000:0000:0000:0000:0000:0000:0001</td><td width="216"><b>::</b>1</td></tr> <tr><td width="288">0000:0000:0000:0000:0000:0000:0000:0000</td><td width="216"><b>::</b></td></tr> </tbody></table> </div> <br /> IPv4 divides its address space into three classes: A, B, and C. IPv6 does not have a concept of classful networks like IPv4. IPv6 subnets or prefixes can be of arbitrary length without any classful boundaries. An IPv6 address prefix is represented by:<br /> IPv6 address / Length of prefix<br /> For example, the following are four different but valid representations of the 64-bit prefix 20010DB80000ABCD:<br /> <div class="stb-grey_box" id="stb-box-6861"> 2001:0DB8:0000:BCD0:0000:0000:0000:0000/64<br /> 2001:0DB8::ABCD:0:0:0:0/64<br /> 2001:0DB8:0:BCD0::/64</div> The last of the above three formats is most commonly used to represent IPv6 prefixes. A node can have an address like 2001:0DB8:0:BCD0:123:4567:89AB:CDEF for the IPv6 prefix 2001:0DB8:0:BCD0::/64.<br /> IPv6 provides two similar options for unicast addressing:<b> </b><br /> <b>Global Unicast</b><br /> IPv6 global unicast addresses are similar to public IPv4 addresses. These addresses are allocated by the Internet Assigned Numbers Authority (IANA) to the Regional Internet Registries (RIRs). RIRs have the task of allocation to services providers and other local registries. IANA maintains an official list of the current state IPv6 address allocation at <a href="http://www.iana.org/assignments/ipv6-address-space/ipv6-address-space.xhtml" rel="nofollow">http://www.iana.org/assignments/ipv6-address-space/ipv6-address-space.xhtml</a><br /> So, each company is assigned a unique IPv6 address block called a <i>global routing prefix</i> – a set of addresses that only one company can use. The company subnets its assigned IPv6 address block using addresses only from the block. As a result, IPv6 global unicast addresses are unique across the globe.<br /> <div class="stb-info_box" id="stb-box-167"> <b>Key Concept </b>IPv6 global unicast addresses and globally unique, and are analogous to IPv4 public address.</div> The term <i>global routing prefix</i> refers to the idea that routers can have one route that covers all the addresses inside an address block, without the need to have individual routes for smaller portions of that block. All IPv6 addresses in a company should begin with the global routing prefix assigned to it. IPv6 has plenty of space to allow all companies to have a global routing prefix with plenty of addresses, thanks to its 128-bit address size.<br /> Global unicast addresses make up the majority of IPv6 address space. <b> </b><br /> <b>Unique Local</b><br /> IPv6 unique local addresses are similar to private IPv4 addresses. These addresses can be used by companies that do not plan to connect to the Internet, and companies that plan to use IPv6 Network Address Translation (NAT).<br /> These addresses are readily available, and you can simply read documentation and start assigning IPv6 addresses without worrying about registration with IANA or another authority. Multiple companies can possibly end up using the exact same IPv6 unique local addresses, and it works just fine just like private IPv4 addresses.<br /> <div class="stb-info_box" id="stb-box-6434"> <b>Key Concept</b> IPv6 unique local addresses are only locally significant and don’t have to be globally unique, just like IPv4 private addresses.</div> <b>Address Range of Global Unicast Addresses</b><br /> Global unicast addresses make up the majority of the IPv6 address space. Originally, Internet Assigned Numbers Authority (IANA) reserved all IPv6 addresses that begin with hex 2 or 3 as global unicast addresses. This address range can be written concisely as 2000<b>::</b>/3. Later, the global unicast address range was made wider by a series of RFCs. The present state of affairs is that all IPv6 addresses not otherwise allocated for other purposes are included in the global unicast address space.<br /> Because the number of addresses that sit within the global unicast address space is astonishingly large, IANA does not assign prefixes from all over the address range.<br /> The type of an IPv6 address can be identified by the initial bits of the address, as explained in below table.<br /> <div align="center"> <b>Table 13-2</b> IPv6 Address Type Identification</div> <table border="1" cellpadding="0" cellspacing="0" style="width: 573px;"><tbody> <tr><td width="141"><b>Address Type</b></td><td width="144"><b>Binary Prefix</b></td><td width="288"><b>IPv6 Notation</b></td></tr> <tr><td width="141">Unspecified</td><td width="144">000…0 (128 bits)</td><td width="288">::/128</td></tr> <tr><td width="141">Loopback</td><td width="144">000…1 (128 bits)</td><td width="288">::1/128</td></tr> <tr><td width="141">Multicast</td><td width="144">1111 1111</td><td width="288">FF00::/8</td></tr> <tr><td width="141">Link-Local Unicast</td><td width="144">1111 1110 10</td><td width="288">FE80::/10</td></tr> <tr><td width="141">Global Unicast</td><td width="144">(everything else)</td><td width="288">(everything else)</td></tr> </tbody></table> <br /> Anycast addresses are taken from the global unicast address space, and are not otherwise distinguishable from unicast addresses.<br /> <b>The Unspecified Address</b><br /> The address 0:0:0:0:0:0:0:0 is called the unspecified address and indicates the absence of an address. It serves as a place holder and must never actually be assigned to a node. As an example of its use, the <i>Source Address</i> field of an IPv6 packet sent by an initializing host before it has learned its own address carries the unspecified address.<b> </b><br /> <b>The Loopback Address</b><br /> The unicast address 0:0:0:0:0:0:0:1 is known as the loopback address, and can be used by an IPv6 host to send a packet to it. The loopback address may be considered the IPv6 equivalent of the IPv4 loopback address 127.0.0.1. The address is reserved for the special purpose of addressing self and must not be actually assigned to an interface. You can think of the loopback interface as a virtual interface to an imaginary link that goes nowhere. The loopback address is treated as having a link-local scope and an IPv6 packet with a destination address of loopback must never be sent outside of a single node.<b> </b><br /> <b>Global Unicast Address Format</b><br /> The general format of global unicast address is shown in Figure 13-2.<br /> <div align="center"> <b>Figure 13-2</b> Global Unicast Address Format<b> </b></div> <b><img alt="Global Unicast Address Format" class="aligncenter size-full wp-image-1188" height="286" src="http://www.freeccnastudyguide.com/wp-content/uploads/2014/05/14-2.jpg" width="872" /></b><br /> <b>Link-Local IPv6 Unicast Address Format</b><br /> The format of link-local addresses that are for use on a single link is given in Figure 13-3.<br /> <div align="center"> <b>Figure 13-3</b> Link-Local Address Format</div> <img alt="14-3" class="aligncenter size-large wp-image-1190" height="238" src="http://www.freeccnastudyguide.com/wp-content/uploads/2014/05/14-3-1024x270.jpg" width="904" /><br /> <div align="center" style="text-align: left;">  Link-local addresses are supposed to be used for addressing of a single link for purposes such as automatic address configuration and neighbor discovery. Routers do not forward packets with link-local source or destination addresses to other links, thus respecting and enforcing link-local scope of these addresses.</div> Site-local addresses were originally designed to be used for addressing inside a site without the need for a global routing prefix. They are now deprecated.

IPv6 Introduction

IP version 4 (IPv4) has been a core part of the TCP/IP protocol suite and has served well during tremendous growth of the Internet. IPv4, ...

Read more »