CCIE Pursuit Blog

February 6, 2009

Where Is The ‘neighbor allowas-in’ Command in the 12.4 Documentation?

I was doing a lab last night that required that you allow prefixes into a BGP AS that had that AS number in the AS-path.  Normally, BGP would drop these advertisements, but I knew that there was a command to allow the local AS in.  I also knew that it was configured as a ‘neighbor’ command.

Weird….I figured that this was something like ‘neighbor allow as’ but I couldn’t find that command in the BGP command reference:

neighbor activate
neighbor advertise-map
neighbor advertisement-interval
neighbor capability orf prefix-list
neighbor default-originate
neighbor description
neighbor disable-connected-check

But there it was on the CLI:

Rack1R3(config-router)#neigh ?
activate                 Enable the Address Family for this Neighbor
advertise-map            specify route-map for conditional advertisement
advertisement-interval   Minimum interval between sending BGP routing updates
allowas-in               Accept as-path with my AS present in it

That’s strange.  I went to the 12.4 Master Command List and it’s there…under:

Cisco IOS Multiprotocol Label Switching Command Reference
neighbor allowas-in

I find it odd that it was not under the BGP command reference, but it’s not a big deal as the name of the command pretty much sums up what it does.  The only (optional)argument that the command takes is the number of times that the local AS can appear in the path.

1 Comment »

  1. I dont think they added it until MPLS VPNs were added.. There was no reason to purposely allow router with your as in it as it would cause a loop on the internet.

    Until mpls vpns.. where you could have a bunch of CE’s using the same AS which had no backdoor connection

    Comment by scott d — February 6, 2009 @ 2:35 pm | Reply

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