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.

[n.elms]

Thankyou @Harold Ritter 

[Harold Ritter]

You are very welcome @n.elms .

You could also refer to the following paper from Geoff Huston for more information.

https://labs.apnic.net/?p=1264

Regards,

[MHM Cisco World]

@Harold Ritter you are always right. 
I always keep learning from you.

[smilstea]

I suggest reading the release notes for these two bugs, they explain the behavior a little more than what is already described in this thread as the reason, more so to the issues this can present. In some instances it could impact the ability to update peer routers with UPDATE messages after an update this large is seen. Largely this is harmless though and we recommend implementing AS length check to prevent such looped updates.

CSCvt66229

CSCvj38301

Thanks,

Sam

[MHM Cisco World]

thanks for this info.

[n.elms]

Thanks Sam,

Please confirm configuring "maxas-limit 20" under BGP would remove the issue/protect against looped AS etc?

In our environment we receive the full BGP table + default so everything would still work.

Thanks,

Neale

[smilstea]

As Hector mentioned the AS length on the internet is usually at most 10 so 20 should work fine, if you want to give a little more room we could consider 30 which would still protect against the prefix you found.

Sam

[n.elms]

Thanks Sam,

What is the equivalent of "maxas-limit 20" in IOS-XR?  I don't see the command

Thanks

[Harold Ritter]

Hi @n.elms ,

In IOS-XR, you will need to implement it using a route-policy as documented in the following post:

https://community.cisco.com/t5/xr-os-and-platforms/ios-xr-bgp-equivelant-of-ios/td-p/3740337

Regards,