2 Replies Latest reply: Jul 16, 2019 2:07 AM by Raynewalk RSS

    Can I mix BGP router ID with update source interface without disruption?

    Raynewalk

      Good Afternoon,

       

      I want to configure an eBGP multihop peering to use ECMP links.  I believe the correct way to do this is by configuring a loopback address and using update-source loopback x for the peering, so BGP will load balance across ECMP.  If that is correct then my question is:-

       

      As we already have BGP neighbors configured over point to point links and a router-id is configured under BGP,  if I configure a loopback will this disrupt these existing peerings and change the router-id.  Or will these peers retain the configured router-id and my ebgp muilt-hop peer use the loopback as the update source.  That is what I want to happen.  So the two types of peer co-exist.  Some using the router-id and some using the loopback, where update-source is configured under the neighbor statement.

       

      Thanks for your help

       

      cheers

       

      Greg

        • 1. Re: Can I mix BGP router ID with update source interface without disruption?
          Ri0N

          Hello Raynewalk,

           

          Not sure I fully understand the question but the BGP router-ID and BGP peering address (including Loopback address) are two different things. You can basically set the BGP router-ID to any IP address - it does not have to be routable on your network, it is merely used to identify the router. The reason the router-ID has the same format as an IP address is that if the router-ID is not explicitly set, it can be derived from the highest Loopback or interface IP address. The BGP peering, however, is configured using real reachable IP addresses. There are different ways of configuring the BGP session. You mentioned setting up an eBGP peering using Loopback interfaces. Configuring a new BGP session using the update-source command would not affect the router-ID.

          • 2. Re: Can I mix BGP router ID with update source interface without disruption?
            Raynewalk

            Thanks.  I wanted to be sure that using update-source on an eBGP peering would not conflict with BGP peers already built with the router ID.  I gather these are independent and update-source is on a per peer basis so I think I have what I need now.