[c-nsp] Full Routes / iBGP Issue & Question

[Spyros Kakaroukas]

Hello,

Path inconsistencies are to be expected, as BGP will only advertise the best routes. Depending on your setup and requirements, you may want to look at advertise-best-external, if you want external routes from both routers to be in the BGP tables.

Prefixes showing up in only one router is kind of weird though. Can you verify that by checking for an exact route ?

PS : You could have pastebinned "sh ip bgp" as well ;)


My thoughts and words are my own.

Kind Regards,

Spyros

-----Original Message-----
From: cisco-nsp [mailto:cisco-nsp-bounces at puck.nether.net] On Behalf Of David Deutsch
Sent: Thursday, September 25, 2014 4:40 PM
To: cisco-nsp at puck.nether.net
Subject: [c-nsp] Full Routes / iBGP Issue & Question

Hello all,

Please excuse my disorganized posting/question, as this is my first posting to the mailing list.

Currently I am attempting to implement two ASR1002-X routers on my network edge, each with diverse eBGP provider connections receiving full routes. Everything up to a point has gone very well, including reception of full routes, blocking of default routes, local prefs, etc. However I am getting some odd results when iBGP connecting the two together.

I appears that certain routes from each other are being filtered out, so each router is in some cases aware of both routes to a prefix and in some cases aware of only one. Examples:

edge01.las.telna.com#show ip bgp
...
*>  1.2.128.0/19     216.115.65.69                  80      0 23005 701
38040 9737 i
  * i                  10.110.5.21              0     80      0 22911
22822 38040 9737 i
  * i 1.2.128.0/18     10.110.5.21              0     80      0 22911
22822 38040 9737 i
  *>                   216.115.65.69                  80      0 23005
701 38040 9737 i
  * i 1.2.128.0/17     10.110.5.21              0     80      0 22911
22822 38040 9737 i
  *>                   216.115.65.69                  80      0 23005
19151 38040 9737 i
  *>i 1.2.160.0/19     10.110.5.21              0     80      0 22911
22822 38040 9737 i
  *                    216.115.65.69                  80      0 23005
19151 10026 38040 9737 i
  *>i 1.2.179.0/24     10.110.5.21              0     80      0 22911
22822 38040 9737 9737 23969 i
  *>i 1.2.180.0/24     10.110.5.21              0     80      0 22911
22822 38040 9737 9737 23969 i
  *>i 1.2.183.0/24     10.110.5.21              0     80      0 22911
22822 38040 9737 9737 23969 i
  *>i 1.2.192.0/19     10.110.5.21              0     80      0 22911
22822 38040 9737 i
  *>i 1.2.192.0/18     10.110.5.21              0     80      0 22911
22822 38040 9737 i
  *>i 1.2.224.0/19     10.110.5.21              0     80      0 22911
22822 38040 9737 i
  * i 1.3.0.0/24       10.110.5.21              0     80      0 22911
174 10026 18046 i

edge02.las.telna.com#show ip bgp
*>  1.0.128.0/19     199.189.118.149                80      0 22911
22822 38040 9737 i
  * i 1.0.128.0/18     10.110.5.11              0     80      0 23005
3356 38040 9737 i
  *>                   199.189.118.149                80      0 22911
22822 38040 9737 i
  * i 1.0.128.0/17     10.110.5.11              0     80      0 23005
19151 38040 9737 9737 i
  *>                   199.189.118.149                80      0 22911
22822 38040 9737 9737 i
  * i 1.0.129.0/24     10.110.5.11              0     80      0 23005
19151 38040 9737 9737 9737 23969 i
  *>                   199.189.118.149                80      0 22911
174 38040 9737 9737 9737 23969 i
  *>  1.0.160.0/19     199.189.118.149                80      0 22911
22822 38040 9737 i

What I don't completely understand is why, when the two ASRs are in a iBGP relationship, some routes are showing on one unit and not the other. Additionally, routes like 1.2.128.0/19 will show both paths on one and not on the other.

edge01 show ip bgp neigh: http://pastebin.com/uv37gsmm
edge02 show ip bgp neigh: http://pastebin.com/Q9SiK1ZZ

edge01 bgp config: http://pastebin.com/rLRDTbDj
edge02 bgp config: http://pastebin.com/apsPLt3D

Any help would be highly appreciated!

--David Deutsch


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