Following is the scenario:
There are 4 routers connected in square formation, D1, D2, C1, C2
D1 is physically connected to C1 and D2
D2 is physically connected to C2 and D1
C1 is physically connected to C2
C1,C2 are in AS-1
D1-D2 are in AS-2
C1-D1 has ebgp peering
C2-D2 has ebgp peering
C1-C2 has IBGP peering
D1-D2 has IBGP peering
Our objective is; all the incoming traffic for prefix 10.0.0.0/8 should come towards D1 under normal conditions:
This ia how I am trying to achieve it;
D1 advertises 10.0.0.0/8 using aggregate address command to C1
D2 advertised 10.0.0.0/8 {2,2} using aggregate address command and a route map for as-path prepend to C2
C1's bgp table:
10.0.0.0/8 pointing -->D1
10.0.0.0/8 {2,2}pointing --> C2
C1's routing table:
10.0.0.0/8 --> D1 ( this is as desired OK)
C2's bgp table:
10.0.0.0/8 -->C1
10.0.0.0/8 {2,2} --> D2
C2's routing table:
10.0.0.0/8 {2,2} --D2 ( this is problematic for me, I want C2 to put the other route that it has learned from C1 in its routing table)
According to CISCO's BGP best path selection, Shortest AS_PATH is preferred first as it is rule # 4. EBGP over IBGP is rule# 7
http://www.cisco.com/en/US/tech/tk365/tk80/technologies_tech_note09186a0080094431.shtml
What's happening at C2 is that C2 is preferring EBGP over IBGP (rule7 and not taking into consideration the as-path length rule 4. There is no specific configuration in bgp of C2 for ignoring AS-Path while making selection. What could be the possible reason or a solution to this problem
I am running 12.1E on 6500s
