In the context of BGP (Border Gateway Protocol) for 6PE (IPv6 Provider Edge) routing over an MPLS network, AFI (Address Family Identifier) and SAFI (Subsequent Address Family Identifier) play a crucial role. They are used to specify the type of network layer reachability information being carried in BGP updates.
For 6PE, the typical values for AFI and SAFI are as follows:
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AFI for IPv6: The AFI for IPv6 is typically set to 2. This value indicates that the BGP session will carry IPv6 address information.
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SAFI for Labeled Unicast: The SAFI for labeled unicast in 6PE is usually set to 4. This value indicates that the BGP session will carry labeled unicast routing information, which is essential for transporting IPv6 over an MPLS network. The labels provided in the BGP updates allow for IPv6 packet forwarding using MPLS labels in the IPv4 MPLS core network.
When a BGP router is configured for 6PE, it uses MP-BGP (Multiprotocol BGP) with this specific AFI/SAFI combination. This configuration enables the router to advertise IPv6 prefixes with MPLS labels to its peers, facilitating the transport of IPv6 traffic over the MPLS backbone without requiring the core network to be IPv6-aware.
In summary, in the 6PE context, AFI is set to 2 for IPv6, and SAFI is set to 4 for labeled unicast, which collectively allow IPv6 routes to be advertised with MPLS labels over an existing IPv4 MPLS backbone.