Appendix D. Multiprotocol BGP (MBGP)
With the support of BGP Capabilities (BGPCAP)[1], Multiprotocol BGP (MBGP)[2] defines backward-compatible extensions to BGP-4[3] that allow it to carry routing information for multiple network layer protocols (for example, IPv6, IPX, and so on). Individual network layer protocols are identified by an Address Family (AF), as defined in RFC 1700[4]. These extensions allow a set of BGP peers to exchange reachability information for multiple AFs (for example IPv4, IPv6, IPX) and sub-AFs (for example, unicast or multicast).
Note
The complete transition plan from the old-style CLI to the new AF-style CLI still has not been completely decided upon within Cisco. For that reason, if you encounter inconsistencies, consult Cisco support personnel or documentation associated with your specific version of IOS.