Couldn't we use 2 /30 subnets on PtP links? 1 /30 with real IPs for ICMP, MTU, reachability etc. and one RFC1918 /30 as secondary for eBGP sessions. I know when a router originates a packet (like with BGP) it sets the source IP to the IP of the interface the packet leaves. Is BGP smart enough when setting up BGP neighbors to use an IP in the same subnet as the neighbor (the secondary interface IP)?
in IOS bgp will bind source ip that is relevant to the subnet it is being peered with, even if it is a secondary ip. i am not sure if it binds the ip to primary ip for the first time, then fall back to secondary ip as primary fails though.. all i know is that when i've tried it by putting a bogus ip as primary, bgp session did turn up, but took a little longer than usual.. didn't investigate any further however. -J -- James Jun TowardEX Technologies, Inc. Technical Lead Network Design, Consulting, IT Outsourcing james@towardex.com Boston-based Colocation & Bandwidth Services cell: 1(978)-394-2867 web: http://www.towardex.com , noc: www.twdx.net