AFI Specific Route Target Distribution
The current route target distribution specification described in RFC4684 defines Route Target NLRIs of maxiumum length of 12 bytes. Furthermore, the current specification mandates that Route Targets exchanged using the current specification are applied towards filtering for all VPN applications that uses the notion of Route Target BGP extended communities. In particular, the same Route Target distribution mechanism is used to exchange VPNv4, VPNv6 and L2VPN prefixes. The IPv6 specific Route Target extended community is defined in RFC5701 as length of 20 bytes. Since the current specification only supports prefixes of maximum length of 12 bytes, the lack of an IPv6 specific Route Target reachability information may be a problem when an operator wants to use this application in a pure IPv6 environment. This document defines an extension to the current constrained route distribution specification that allows BGP speakers to distribute Route Target prefixes using multiple different Address Families thereby limiting the application of Route Target prefix filters to the specific address family under which it is advertised. Furtheremore, this document defines an extension that allows BGP to exchange longer length IPv6 Route Target prefixes.