something strange about bgp community
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
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@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@gmail.com
On Wed, Jan 7, 2015 at 9:29 AM, Jared Mauch <jared@puck.nether.net> wrote:
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.
it looks like this is the 'customer' of several networks (701, 2914) and they just blindly add carrier communities to their routes 'everywhere'... Or perhaps they view the RV peer as a special place to signal their intent on certain routes more clearly? "Hey, this route is going to get localpref 120 in 701 and NOT be announced to 2914" either way, unless someone strips them, the communities just stay around until stripping... -chris
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@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@gmail.com
Also note there is nothing stopping anyone from adding any community they want. The effect and how long the community stays attached to a route is another matter. On 1/7/2015 8:35 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!
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!
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
Hi Song, that's normal. This is a signat to AS702 to do some special with this route when it will see this route. Community is transistive by its design, so you don't need to be directly connected to AS702 to send some signal to it. For example: you->AS101-AS102-AS103-target \->AS104-/\/\/\-AS105-/ where /\/\/\ is disrupted path with packet loss. AS104-AS105 is better as AS-PATH lengh. If "target" accepts community, I can add "target:notaccept" to AS104 and avoid that path. Some brain-dead ;) transit providers clear all community when import announces, but for me it is at least unfair. On 07.01.15 15:35, 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!
On Thu, Jan 8, 2015 at 9:50 AM, Max Tulyev <maxtul@netassist.ua> wrote:
Some brain-dead ;) transit providers clear all community when import announces, but for me it is at least unfair.
hrm, it's possible that cleaning the communities (after dealing with the local/customer-added ones) means you may not get multiple copies that differ only in community in your network. this may have the effect of you seeing less route 'churn' overall in your network.
participants (6)
-
Christopher Morrow -
Jared Mauch -
joel jaeggli -
Max Tulyev -
ML -
Song Li