----- Original Message ----- From: "Przemyslaw Karwasiecki" > 5) In phase 5 some of eBGP routes which has lost > in BGP selection in phase 3 and has been advertised > over iBGP in phase 2 needs to be withdrawn
Yes, that's exactly what is happening, but that represents a change! (And is ultimately the point of my original post) The selection process hasn't changed... All of the old rules apply... The change is that the iBGP peers never used to issue withdraws in the past. Those alternative, less attractive paths always remained in the Adj-RIB-in table of a router, and if the installed route for a prefix needed to come out due to the loss of an external peer, or a withdraw from that peer, the formerly less attractive route could be promoted, and installed. Now, instead of the local router promoting the less attractive route itself, it does not have that route in it's Adj-RIb-in. It forwards the withdraw notice to it's iBGP peer, which turns around and advertises that prefix back to the peer, and it then gets installed. This represents a change in the way the Cisco code is treating these less preferred routes. As I mentioned in another post, this is a very clever change, in that it reduces the amount of memory consumed by these less preferred routes, and from a functional standpoint, all of the redundancy of full peering connections to multiple upstream ISPs is preserved. Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=34561&t=34561 -------------------------------------------------- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
