[c-nsp] eBGP via loopback

[Steve Bertrand]

Hi everyone,

I'm having an issue delivering packets in a test environment that I have.

To make it as simple as possible, I'll describe what I have with all 
links disconnected except for the problematic one. My inquiries are not 
really regarding the packet loss, but more about BGP implementation itself.


coe router --------- fibre --------- cpe router
ebgp multihop (loopback) ---------- ebgp multihop (loopback)
default-orig ---->----->----->----- default points to coe loopback
/29 over loopback ----<-----<------ advertise /29 via loopback

Unfortunately, I'm not aware of any tcpdump type software on a Cisco, so 
I don't know exactly where the packets are failing.

The devices can communicate back and forth whether it be over the actual 
interface PtP IPs, or the loopback addresses themselves.

If I direct a packet in from a separate interface on COE, I receive ping 
responses from all IPs, on all interfaces on that router. Attempting to 
ping any IP on the CPE, the traffic goes in, but I see no evidence that 
it is attempting to be sent out to the CPE destination.

I'm fairly certain I'm missing something quite silly here, but before I 
spend any more time trying to test out my own personal educational 
theories, I thought I'd ask opinion on two thoughts I'm having. I'm 
hoping that the fine engineers here can steer me in the right direction.

- using loopback with eBGP could possibly have a detrimental effect by 
trying to re-establish a BGP session to the remote loopback via a 
different multi-homed path that already has an established eBGP session.

- in contrast to iBGP where there are usually multiple physical paths to 
a peer's loopback, eBGP is designed for PtP, so if the interface, link 
or remote interface goes down, you want BGP to notice that anyway and 
rebuild the routing table around the problem

The loopback isn't the problem in the packets getting through as far as 
I can tell, but I just wanted an opinion whether I'm on the right track 
here with the utilization of loopbacks, or if I've been simply thinking 
about this too hard.

Regards,

Steve