optional transitive attribute in bgp

[singhankit685]

when a router receives a route with an optional transitive attribute will it install the route in its routing table  (case: if it does not recognise the attribute) before passing the route to its peer??and also what is does in case if it receives a route with a non -transitive attribute??

[milan.kulik]

Hi,

as you can read here

http://www.informit.com/articles/article.aspx?p=331613&seqNum=5

"

• Optional transitive attributes; these attributes may be recognized by some BGP speakers, but not all. They should be preserved and advertised to all peers whether or not they are recognized.

• Optional non-transitive attributes; these attributes may be recognized by some BGP speakers, but not all. If an update containing an optional transitive attribute is received, the update should be advertised to peers without the unrecognized attributes."

The attribute can be advertised to a peer with a prefix only.

And a BGP router is always advertising only the prefix with the best path from his BGP table.

(See http://www.cisco.com/c/en/us/support/docs/ip/border-gateway-protocol-bgp/19345-bgp-noad.html ).

So the prefix has to be present (=accepted) in the router BGP table first.

(Not necessarilly passed to the router RIB to be 100% precise.)

Best regards,

Milan

[singhankit685]

in the case of optional non-transitive attributes, will the router receiving the route install the route in its routing table if it doesnt recognise the attribute ?? ans also what it will do if it recognises the attribute , will it pass the attribute to its peer ??

[milan.kulik]

Hi,

"yes" to both questions!

Best regards,

Milan

[singhankit685]

@milan kulik , thank you!!