BGP, ebgp-multihop and multiple peers

Steve Bertrand steve at
Tue Aug 26 18:48:23 CDT 2008

Hi everyone,

This question comes after likely overlooking an IETF document or BCP 
that describes what I'm after. Given that I am looking for advice from 
someone who is more experienced operationally in this regard than me, 
and that this technically is an implementation-neutral question, I 
wanted to ask here.

Taking one router I have as an example, I have four IPv6 BGP peers (two 
are for true routing, the other two for route server projects), and five 
IPv4 BGP peers. Two of the v4 peers are Cymru for BOGONS, the other 
three are purely outbound to route server projects. All five v4 peers 
are ebgp-multihop.

I'm looking for advice on the configuration of the peers with 
ebgp-multihop (IPv4).

I have a reserved block carved out of my allocation specifically for 
/32s on loopbacks, and when I light up a new peer, I configure a new 
looopback interface for that peer, and subsequently give it the next 
available IP from the reserved /32 block.

There are numerous drawbacks to doing it this way... waste of IPv4 
addresses, additional keystrokes on the router for interface config, 
documentation, expanded margin for error et-al.

There are a few benefits to doing it this way (IMHO), but I see obvious 
benefits of using a single loopback interface and single IP for ALL of 
these multihop peers. Before I state good/bad, or get any wrong idea in 
my head, I'd like to ask the real experts here which way they would/do 
this type of thing, and why.

- single loopback/single IP for all peers, or;
- each peer with its own loopback/IP?



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