The current route target distribution specification described in
RFC4684 defines Route Target NLRIs of maximum length of 12 bytes.
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 that allows BGP to
exchange longer length IPv6 Route Target prefixes.