11-25-2013 09:54 PM - edited 03-04-2019 09:41 PM
Hi All,
I have created a simple topology in GNS3. ( Please refer attached config and topology )
EBGP between R1 and R2 , R1 and R3.
Routes are NOT advertised to R3 and R2 from R1 ,which are learnt from R2 and 3.
R1 AS number is 65000
R2 and R3 AS number is 65457
R1 NOT advertising routes to R2 which comes from R3 ( may be AS number is the same)
Please advise , should I configure some special command to achieve this.
Thanks
Sri
Solved! Go to Solution.
11-25-2013 11:49 PM
Hi,
in BGP the loop prevention mechanism is the AS_PATH so when R1 sends the BGP update to R2 it contains R3 AS which is also R2 AS so when R2 sees its own AS in the AS_PATH it considers there was a loop and doesn't accept the update.
You can use the allow-as-in feature to disable the loop prevention mechanism per neighbour.
http://ccieblog.co.uk/bgp/bgp-as-override-vs-allow-as-in
Regards
Alain
Don't forget to rate helpful posts.
11-25-2013 11:49 PM
Hi,
in BGP the loop prevention mechanism is the AS_PATH so when R1 sends the BGP update to R2 it contains R3 AS which is also R2 AS so when R2 sees its own AS in the AS_PATH it considers there was a loop and doesn't accept the update.
You can use the allow-as-in feature to disable the loop prevention mechanism per neighbour.
http://ccieblog.co.uk/bgp/bgp-as-override-vs-allow-as-in
Regards
Alain
Don't forget to rate helpful posts.
11-26-2013 02:31 AM
Thank you very much Alain, I will test it out tomorrow and get back to you.
I guessed, it blocked due to SAME AS but did NOT know how to block it.
Thanks
Sri
11-26-2013 09:46 PM
Alain, it works! thanks once again :-) - Sri
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