BGP Advertising sequence

[jpazahanick]

When a new BGP peer comes up, what process (or in what order) are routes advertised to the peer?  Does it advertise the oldest routes in the Local RIB first?  Longest?  Completely random?

[jcozzupoli]

Hello,

Please see the BGP Path Selection Algorithm which shows what attributes are preferenced in order for a route to be placed into the RIB:

http://www.cisco.com/en/US/partner/tech/tk365/technologies_tech_note09186a0080094431.shtml

To answer your question, the Oldest path is the 10th attribute looked at for path installation into the RIB.

Cheers,

Joe.

[jpazahanick]

Thanks for the reply;  I understand the selection process for placing the route into the RIB;  my question is going the other way;  it what sequence does it advertise routes to other peers, upon establishing a new session...

[ashok_boin]

Hi,

It's a nice question which might be answered by BGP developers

I guess the sequence starts with lowest to highest 1st octet OR highest origin routes first (connected routes, internal routes and then redist routes).

Regards...

-Ashok.