Fail to establish a non-directly connected BGP peering

[morris0117]

Greetings,

In GNS3, I deploy 3 routers: R7, R8 & R9. The physical connection is like R7-R8-R9.

R7 has established BGP peering with R8, so do R8 & R9, with update-source loopback0.

There are static routes 0.0.0.0 0.0.0.0 set in R7 & R9 with port interfaces on R8 as their next-hop.

There are static routes set in R8 to reach loopback0 of R7 & R9.

I can ping R9's loopback0 from R7 and vice versa.

Now I want to establish BGP peering between R7 & R9 but the debug shows "active open failed - no route to peer". Please help.

Configurations are attached.

Thanks all!

[M02@rt37 · Accepted solution]

Hello @morris0117,

On R7 add:

route 9.9.9.9 255.255.255.255 192.168.78.8

On R9 add:

ip route 7.7.7.7 255.255.255.255 192.168.89.8

After that, peering iBGP beween R7 and R9 should be Established. Default route is not sufficient in this case where R7 and R9 are not directly connected.

R7 and R9 need specific static route ! You should consider also to configure R8 as route-reflector also...

[morris0117]

Thank you, it works. But I got a few questions:

1. Why is the default route not sufficient in this case?

2. Why does it work even I only configure the static route on R7. And is there any risk if I don't configure the s-route on R9? (This make me think of a similar issue: For R7 & R8, if I configure the

nei <ip> update-source lo0

only on R7, it can establish BGP with R8, but I wonder what would happen if I don't do it on R8...)


Yes I was about to perform a RR experiment after clarifying these questions.

Thanks again!

[Harold Ritter]

Hi @morris0117 ,

Cisco IOS does not allow a bgp session to be established using the default route to resolve the peer address. You will need a more specific route as M02@rt37 proposes.

Regards,

[MHM Cisco World]

You ned one side only use static route other you can use default or static

You need (only for ebgp) 

Ebgp multihop for any non direct bgp peer, or disable direct connection check

MHM

[MHM Cisco World]

Remove redistribute static and keep other config as it and check

MHM

[MHM Cisco World]

Let agree that only one side need static route other can use static route or default 

Now months ago same issue happened and in that time I dont know reason but after some check I get issue.

RouteA-RouterB 

RouteA have staitc route for RouterB LO 

RouterB have defualt route for RouterA LO 

The ibgp work but until redistrubte connect add to RouterA 

The issue appears 

RouterB have now two path defualt and bgp to LO of RouterA 

So to reach bgp peer use bgp itself!!!!!

That break ibgp 

Your issue same 

The middle router redistrubte static to other router and make it use bgp path instead of default.

That why I mention remove redistrubte static.

It seem simple issue but in real network you never detects it.

MHM