Use of BGP for dissemination of ILA mapping informationFacebook1 Hacker WayMenlo ParkCA94025USpetr@fb.com
Routing
Inter-Domain RoutingInternet DraftBGPILAIdentifier-Locator Addressing relies on splitting the 128-bit IPv6 address into identifier and locator parts to implement identifier mobility, and network virtualization. This document proposes a method for distributing the identifier to locator mapping information using Multiprotocol Extensions for BGP-4.
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.
Under the ILA proposal, the IPv6 address is split in 64-bit identifier (lower address bits) and locator (higher address bits) portions. The locator part is determined dynamically from a mapping table that maintains associations between the location-independent identifiers and topologically significant locators. The hosts that collectively implement and maintain such mappings are referred to as "ILA domain" in this document. The ILA domain has a globally unique 64-bit SIR (Standard Identifier Representation) prefix assigned to it (see for more details on SIR prefix use).
This document proposes a new address family identifier (AFI) for the purpose of disseminating the locator-identifier mappings among the nodes participating in the ILA domain. For example, this extension could be used to propagate the mappings from ILA hosts to ILA routers and allow the routers to perform their function (see for definition of the "ILA router" functions).
This document introduces a new AFI known as a "Identifier-Locator Addressing AFI" (ILA AFI) with the actual value to be assigned by IANA. The purpose of this AFI is disseminating the mapping information in the ILA domain, e.g. between ILA hosts and ILA routers. This document defines the use of SAFI values of "1" (unicast) and "2" (multicast) only.
A BGP speaker that wishes to exchange ILA mapping information MUST use the Multiprotocol Extensions Capability Code, as defined in , to advertise the corresponding AFI/SAFI pair.
For the purpose of ILA mapping encoding, the 8-octet locator field SHALL be encoded in the "next-hop address" field. The "length of the next-hop address" MUST be set to "8". The identifiers bound to the locator SHALL be encoded within the NLRI portion of MP_REACH_NLRI attribute. The NLRI portion of MP_REACH_NLRI starts with the two-octet "Length of identifiers" field. The rest of the NLRI is a collection of 8-octet identifiers that are bound to the locator specified in the "next-hop address" field.
Withdrawal of ILA mapping information is performed via an MP_UNREACH_NLRI attribute advertisement organized as following:
Only the locator part of ILA address is used for packet routing, and every node that hosts an identifier MUST have a unique routable /64 prefix within the scope of the ILA domain. The identifiers advertised under the ILA AFI are expected to be used by the data-plane implementation to perform match on a full IPv6 address and decide whether the locator portion of the address needs a re-write. It is up to the implementation to decide which full 128-bit IPv6 addresses need a rewrite, e.g. by matching on a Standard Identifier Representation (SIR) prefix as defined in .
The locator rewrite information comes from the next-hop "address" associated with the identifier. The next-hop field of MP_REACH_NLRI attribute MUST NOT be used for any routing resolutions/lookups by the BGP process itself. It should be used purely to create a rewrite rule in the data-plane forwarding table. The actual forwarding decision is then based on subsequent lookup in the forwarding table to find the next hop to send the packet to.
For multicast packets, the RPF check process SHALL be modified for use with ILA source addresses. Specifically, source ILA IPv6 addresses with the identifier portion matching the mapping table SHALL be mapped to proper locator, prior to performing the RPF check. The ILA source addresses need to be identified by some means specific to ILA implementation, e.g. by matching on configured SIR prefixes. The ILA addresses that do not match any mapping entry SHALL be considered as failing the RPF check.
The ILA mappings are only unique with an ILA domain - it is possible that different domains may re-use the same identifiers. To make identifiers globally unique, they MUST be concatenated with the SIR prefix assigned to each ILA domain. These globally unique identifiers may then be exchanged among the ILA domains. For the purpose of facilitating this exchange, IANA will be requested to allocate new SAFI value called "VPN-ILA" SAFI. The MP_REACH_NLRI attributes exchanged over this SAFI will look as following:
The main change from the Unicast/Multicast SAFI's is presence of the SIR prefix field in the announcement. Correspondingly, the MP_UNREACH_NLRI will look as following:
The use of domain-specific identifiers would require the ILA hosts and routers to make their ILA cache lookups based on the full 128-bit prefix.
It could be useful to bind multiple locators to the same identifier, e.g. for the purpose of load-sharing. To make announcing multiple locators possible, the MP_REACH_NLRI and MP_REACH_NLRI attributes are extended to encode the path-identifier per , correspondingly enabling the capability for the AFI/SAFI. Specifically, the NLRI field will look as following:
This encoding instructs the receiver to create multiple locator entries for an identifier, differentiated by their path identifiers. Optionally, a weight could be associated with each path using the "link bandwidth" extended community defined in
For the purpose of this work, IANA would be asked to allocate a value for the new AFI, and the VPN-ILA SAFI.
TBD
This document does not introduce any changes in terms of BGP security. Defining ILA security model is outside of scope of this document.
The author would like to thank Doug Porter for the initial idea and discussion of this proposal.