ASR9K BGP Error

[n.elms]

Hi all,

We've received the following log message on our ASR9K for the last few days. Always for the same prefix (45.70.224.0/22).

4446 RP/0/RSP0/CPU0:Oct 14 09:54:22.337 UTC: bgp[1087]: %ROUTING-BGP-4-OVERSIZED_UPDATE : [20] : There was and attempt to generate an oversized update message when advertising prefix 45.70.224.0/22 in table "TBL:default (1/1)" / update-group 0.2 / sub-group 0.1. Message details: total size 4106, attributes size 4031, NLRI size 5 : pkg/bin/bgp : (PID=956633470) : -Traceback= 40022690 4002e2ac 4002e894 f21c4688 f21c52d8 f6b48b28 f6b48e70 f6b4a198 f21c7560 4001ac50 f6b48b28 f6b48d38 f6b49ed4 40025284 40025fb8 40026a0c

Is this something to be concerned about?  I have searched and find nothing for %ROUTING-BGP-4-OVERSIZED_UPDATE messages.

Thanks.

[balaji.bandi]

how is your config, check maximum prefix :

https://www.cisco.com/c/en/us/support/docs/ip/border-gateway-protocol-bgp/25160-bgp-maximum-prefix.html

[n.elms]

Thanks Balaji,

I already have max-prefix configured, it's not that triggering it.

[balaji.bandi]

in that i need to investigate, is this from one AS or you have diffrent AS ?

[MHM Cisco World]

try run 
path-mtu-discovery 
to make update message not larger than TCP-MSS.

[n.elms]

Thanks I will try that suggestion - I need to do it under change.

[n.elms]

Hi MHM,

I have MTU 9212 (MSS 9158) bytes between my 2 routers and MTU 1514 bytes to my providers.  I can see my MSS is 1460 but I am thinking the error does not indicate which connection this error is happening on.  Any ideas? 

[MHM Cisco World]

see below comment 

[tkarnani]

An example of this can be an aspath that is too long (looping for example) or possibility too many attributes attached to this prefix can we check

show bgp ipv4 unicast 45.70.224.0/22  detail ?

Thank you

[n.elms]

Hi tkarnani,

Here it is.. AS PATH looks super long.  I think you found the issue!

BGP routing table entry for 45.70.224.0/22
Versions:
Process bRIB/RIB SendTblVer
Speaker 399222546 399222546
Flags: 0x00003001+0x00000000;
Last Modified: Oct 14 12:12:38.036 for 00:00:14
Paths: (1 available, best #1)
Advertised IPv4 Unicast paths to peers (in unique update groups):
212.21.96.1
Path #1: Received by speaker 0
Flags: 0xc000000001048003, import: 0x20
Advertised IPv4 Unicast paths to peers (in unique update groups):
212.21.96.1
13237 2914 174 53013 270814 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590
267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590
267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 2
67590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 26
7590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267
590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 2675
90 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590 267590, (received & used)
84.207.204.106 from 84.207.204.106 (82.197.136.1)
Origin IGP, localpref 100, valid, external, best, group-best
Received Path ID 0, Local Path ID 1, version 399222546
Community: 2914:420 2914:1205 2914:2204 2914:3200 13237:44044 13237:46442
Origin-AS validity: (disabled)

[MHM Cisco World]

sure there are many same AS in path.

[n.elms]

I think there is no error my side here then, the advertisement for 45.70.224.0/22 and 45.70.226.0/23 is the problem.  Too many AS in the path as you will see above (267590 267590 267590...).

Thanks for your help everyone.

[MHM Cisco World]

There iş workaround, config max as-path length accpet, check this solution.

[n.elms]

I see there is also maxas-limit [1-2000]

Now the question is what is a sensible value to use here?

[Harold Ritter · Accepted solution]

Hi @n.elms ,

Any BGP prefix seen on the Internet on given day would normally have an as path not longer than 10. You could use 15 or 20 to be safe.

Regards,

Regards,