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BGP can advertise a whole bunch of AFI/SAFIs, one of them is IPv4/IPv6 labeled unicast. I was wondering what are the practical applications of this kind of route? And how is it different from a VPN route? From what I understand in both cases a label is attached to the advertised prefix. (Is the difference that VPN allocates a label per VRF, and in the labeled unicast case a label is allocated per route?)

From my research I found out that IPv6 labeled unicast is used in 6PE scenarios, where the core MPLS network is IPv4 and is used to connect between IPv6 speaking PE routers. What are the use cases for IPv4 labeled unicast then? To connect IPv4 speaking PE routers over an IPv6 MPLS core? (Does it have a formal name 4PE??) Any other use cases ?

Please help me clear my understanding. Thanks.

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BGP-LU is used where you need to join multiple networks together (e.g.: running distinct IGPs) while still being able to provide a transport label between any two nodes.

A couple of use cases that come to mind:

  • Large cellular backhaul network - may have 10s of thousands of base stations. It wouldn't be feasible to have these all participate in a single (say) OSPF area and distribute link-nets and loopbacks. Using BGP-LU you could break it up into regional IGPs, but still establish end-to-end LSPs across regions to a centralised head-end

  • Merging two existing networks together - you're a large ISP running OSPF as your IGP, and you acquire another large ISP running IS-IS as it's IGP. With BGP-LU you can create LSPs across these two networks without having to perform some unholy route re-distribution between two link-state protocols.

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