something strange about bgp community

Wed Jan 7 14:29:36 UTC 2015

2914:429 is a community to signal to NTT to not announce the route to peers which would perhaps be why you don't see NTT doing that. 

You can see the documented NTT communities here: http://www.us.ntt.net/support/policy/routing.cfm

Jared Mauch

> On Jan 7, 2015, at 5:35 AM, Song Li <refresh.lsong at gmail.com> wrote:
> 
> Hi everyone,
> 
> Today when I check one route in Routeviews I find something strange as follows:
> 
> route-views>sh ip bgp 176.108.0.0
> BGP routing table entry for 176.108.0.0/19, version 23405621
> Paths: (33 available, best #28, table default)
>  Not advertised to any peer
>  Refresh Epoch 1
>  202018 35320 35320 57800
>    5.101.110.2 from 5.101.110.2 (5.101.110.2)
>      Origin IGP, localpref 100, valid, external
>      Community: 702:120 2914:429 20485:52990 20485:53990 20485:54040 20485:54050 47541:10001
>      rx pathid: 0, tx pathid: 0
> 
> the AS-Path is "202018 35320 35320 57800" but the community is 702:120 2914:429 20485:52990 ....
> 
> According to RFC 1997, the community format is AA:NN and AA means the AS#. Here, AS702, AS2914 and AS20485 do not appear in the AS-Path and as a result they should not appear in the community. Could anybody tell me what's the reason they do appear in the community of this route?
> 
> Thanks!
> 
> -- 
> Song Li
> Room 4-204, FIT Building,
> Network Security,
> Department of Electronic Engineering,
> Tsinghua University, Beijing 100084, China
> Tel:( +86) 010-62446440
> E-mail: refresh.lsong at gmail.com