BGP Confederation Identifier in sub-AS

[Johannes_Grimm]

Dear community,

why is it necessary to configure the command bgp confederation identifier XXX within a Confederation AS? I understand that the command is necessary in eBGP peerings, but within an AS I could not find a package that transmits this value?

I have three routers implemented in a confederation sub AS in my lab.

R1 (Route Reflector Client) -- R2 (Route Reflector) -- R3 (Route Reflector Client)

R1 has eBGP peering to another AS and to a Confederation sub AS. R3 has only one peering to a Confederation sub-AS.

I initially set the value for the identifier on R2 differently than on R1 and R3 - with no effect. Afterwards I removed the value completely and still could not find any effects. Also, when I redistribute a route in BGP from R2 using the Network Statement, the route is propagated cleanly inside and outside the Confederation.

I also can't figure out in which packet the Confederation Identifier is transmitted in the AS. Neither in the BGP OPEN message, nor in updates the Confederation Identifier is transmitted.

However, the necessity of this command also within a sub-AS is described in all documentation known to me.

Did I miss something or is it just good style to configure the identifier in the whole AS?

Thanks, 

Johannes

[Harold Ritter]

Hi Johannes,

The RR in your scenario doesn't not need to be configured with "bgp confederation id" (nor "bgp confederation peers") if it doesn't peer with anyone outside the sub AS or outside the AS.

Regards,

[Johannes_Grimm]

Hi Harold,

thank you very much for your answer. Is there any use case scenario where configuring the bgp confederation id within a sub AS is necessary if the router is not connected to another AS? My understanding is that only routers that peer with other AS need this.

Best regards,

Johannes

[Harold Ritter · Accepted solution]

Hi Johannes,

The "bgp confederation id" is not used in such a case. Configuring it is useless.

Regards,