MP-BGP and Address Families

BGP originally only supports normal IPv4 unicast prefixes. With the passage of time & advancement in Network Technology, the need for support of more prefix types arose. There were two solutions to this problem:

Of course, we chose the second one due to its flexibility & backward compatibility. Hence, MP-BGP came into existence under RFC4760 (https://tools.ietf.org/html/rfc4760) in 2007. MP-BGP supported more than 15 different BGP address families and it solved the problem.

Nowadays MP-BGP (Multiprotocol BGP) is a normal practice which supports different addresses including IPv4, IPv6 & so on. It is simply an extension to BGP that enables BGP to carry routing information for multiple network layers and address families.

AFI/sAFI:

These are simply the names or ID’s of the BGP Address Families.

AFI: Each Address Family in BGP is identified by the Address-Family Identifier (AFI). It carries the identity of the Network Layer protocol associated with the Network Address that follows. For example, these are the most common AFI’s:

sAFI: Within each AFI there is a Subsequent Address Family Identifier. It provides additional information about the type of the Network Layer Reachability Information carried in the attribute. For example, these are the most common sAFI’s:

So, it means 1/1 will mean IPv4 & Unicast as in below examples:

List of AFI/sAFI:

Below is the full list of all AFI/sAFI’s for reference. Each Network Equipment vendor is free to choose which one it wants to be supported on which of its equipment Hardware & Software/IOS. e.g.

– Pre 12.2 Cisco IOS supports only four AFI’s (IPv4, IPv6, CLNS, VPNv4)

– Cisco IOS Release 12.2(33)SRB, and later releases, support for the L2VPN address family and VPLS sAFI

Below output shows all the AFI’s & sAFI’s supported by Cisco IOS 12.2 as an example:

Full list of AFI’s & sAFI’s as defined by IANA is as in below: