Re: something strange about bgp community

[Song Li <refresh.lsong () gmail com>]

Thanks!

Because there is no standard syntax on the description of BGP community, 
I think the problem is hard to understand.

在 2015/1/7 23:25, joel jaeggli 写道:
> 2914:429 is ntt's do not advertise to any peer community
>
> bgp communities are transitive attributes, e.g. you can just pass them
> to peers unmolested.  so someone that's presumably not ntt ( e.g. the
> neighbor is digital ocean) is sending that commmunity to route views as
> part of their export.
>
> Their utility in routviews depends on context, when I see communities I
> tagged on my own routes in routviews for example I can tell what pop the
> announcement  originated from which is rather useful. other's like the
> one above do tell you something about the policy of somebody on the
> internet. you can also tell who strips communities...
>
> On 1/7/15 5:35 AM, Song Li 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 () gmail com