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As RD is part of VPNv4 (A.K.A - IPv4 VPN) NLRI and is exchanged between PE routers participating in a L3VPN service. Should RD value be unique only within a given PE router or should it be unique among all PE routers?

If RD is only locally unique within each PE router - this might cause the same route to appear more than once in the global BGP routing table, doesn't it?

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If RD is only locally unique within each PE router - this might cause the same route to appear more than once in the global BGP routing table, doesn't it?

In theory, yes, as it would in "ordinary" IP routing. Also, as in IP routing, BGP will select only one route to put in the BGP table.

In practice, you would never assign the same RD to more than one customer. The whole point of RDs is to keep different customer's routes separate

As a general practice, it's a good idea to give every VRF a unique RD. That way, you can tell quickly which PE sourced the route -- helpful for troubleshooting. Remember that RD does not define a VPN. It just makes routes advertised by that router unique.

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  • Can you explain why they won't appear in the global table? I thought that this was the whole purpose of RD - to make it unique in global tables. In global BGP table a VPNv4 route exists in the form of RD:prefix, doesn't it?
    – manish ma
    Jun 15, 2022 at 18:59
  • I was referring to the global route table. I'll rewrite my answer to clarify. But briefly, you would not assign the same RD to different customers, for exactly the reason you mention.
    – Ron Trunk
    Jun 15, 2022 at 19:25

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