BGP Neighbors

  • When connecting to a BGP neighbor that is dual-homed, using loopbacks is recommended although the “update-source x” command must be used to ensure the router sources packets from that loopback interface.
  • Basic neighbor configuration commands with loopbacks:

    router bgp 5500
    no auto-summary
    bgp log-neighbor-changes
    neighbor 1.1.1.1 remote-as 5500
    neighbor 1.1.1.1 update-source Loopback4
  • For eBGP neighbors, a rule applies by default whereby eBGP neighbors must be directly connected. Neighbors that have the update-source parameter set to a loopback interface are not seen as being directly connected (they are seen as one hop away) and therefore neighbor relationships will not form.  Therefore ebgp-multihop needs to be enabled.
  • Basic eBGP neighbor configuration commands with loopbacks:

    router bgp 5500
    no auto-summary
    neighbor 5.5.5.5 remote-as 6500
    neighbor 5.5.5.5 ebgp-multihop 2
    neighbor 5.5.5.5 update-source Loopback4

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