BGP add-path RX

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BGP add-path RX is an experimental feature in Cumulus Linux, that allows BGP to receive multiple paths for the same prefix. A path identifier is used so that additional paths do not override previously advertised paths.

Note: Cumulus Linux only provides the receiving (RX) add-path functionality. Transmitting functionality (TX) is not available in this release.

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Environment

  • BGP add-path RX is available in Cumulus Linux 2.5.0 and later. 

Configuration

No additional configuration is required for BGP add-path RX.

To view the existing capabilities, run show ip bgp neighbors. They can be seen listed in the subsection Add Path:, below Neighbor capabilities:.

BGP neighbor is 10.0.0.7, remote AS 100, local AS 100, internal link
...
  Neighbor capabilities:
    4 Byte AS: advertised and received
    AddPath:
      IPv4 Unicast: TX received
      IPv4 Unicast: RX advertised and received
...

The example output above shows that additional BGP paths can be received (RX is advertised), but not sent (TX is not advertised). It also shows that the BGP neighbor, 10.0.0.7, supports both.

To view the current additional paths, run show ip bgp network:

# show ip bgp 1.1.1.1/32
BGP routing table entry for 1.1.1.1/32
Paths: (3 available, best #2, table Default-IP-Routing-Table)
  Not advertised to any peer
  Local
    56.56.56.56 (metric 30) from 10.0.0.7 (10.0.0.5)
      Origin IGP, localpref 100, valid, internal
      Originator: 10.0.0.5, Cluster list: 10.0.0.7
      AddPath ID: RX 1, TX 0
      Last update: Thu Oct  1 18:43:20 2015
  Local
    12.12.12.12 (metric 30) from 10.0.0.7 (10.0.0.1)
      Origin IGP, localpref 100, valid, internal, best
      Originator: 10.0.0.1, Cluster list: 10.0.0.7
      AddPath ID: RX 4, TX 0
      Last update: Thu Oct  1 18:43:20 2015
  Local
    34.34.34.34 (metric 30) from 10.0.0.7 (10.0.0.3)
      Origin IGP, localpref 100, valid, internal
      Originator: 10.0.0.3, Cluster list: 10.0.0.7
      AddPath ID: RX 5, TX 0
      Last update: Thu Oct  1 18:43:20 2015

The example output above shows two additional paths that have been added by the TX node for receiving. All three paths have a unique AddPath ID.

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