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Forum Replies

  1. Hi Hamood,

    That’s right, if you source eBGP from the loopback interfaces then you’ll need multihop.

    The problem with the R1-R2-R3 scenario is that R2 will never learn about any prefixes, when R1 tries to reach a network behind R3 (or R3 wants to reach something behind R1) then R2 will receive an IP packet with a destination it doesn’t know about.

    If you really had to use eBGP between R1 and R3 then a GRE tunnel might be a solution…

    Rene

  2. Hi Rene,

    Why you enable the directly connected check again when you increase the TTL ?

    thanks.

  3. thanks Rene I understood that we have tow options to use, but in the first option they will not become neighbor even though “disable-connected-check” since by default the TTL for eBGP is 1 so finally we need to increase the TTL if we use the first option ? right ?

  4. In your example R1:

    R1(config)#router bgp 1
    R1(config-router)#neighbor 2.2.2.2 remote-as 2
    R1(config-router)#neighbor 2.2.2.2 update source loopback 0
    R1(config-router)#neighbor 2.2.2.2 ebgp-multihop 2
    

    You said “we also have to use the update-source command to tell the routers to use the IP address on their loopback interface as the source IP address for the eBGP neighbor adjacency”

    The 2nd command “neighbor 2.2.2.2 remote-as 2” – what does that do? That doesn’t establish R2 as the source?

  5. I’m still not clear on why the second scenario requires multihop when the neighbours are directly connected.

    Are you saying that when traffic is sourced from and to a loopback, it is effectively taking 3 hops? (2 of which are virtual within the routers).

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