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Re: BGP, ebgp-multihop and multiple peers

  • From: Truman Boyes
  • Date: Tue Aug 26 21:41:59 2008
Steve,

You ask a very good question because I have seen some providers embark on the multiple loopback approach for numerous reasons. I suggest a single loopback per routing-instance whenever possible. The cost savings in OSS and integration in routing configurations with a single repeatable block of configuration per peer/peer group is far more beneficial than some corner case technical benefit of having multiple loopback addresses.

I have been forced for other feature support to deploy multiple loopback interfaces, but have always opted to keep all EBGP peering with a single loopback interface per routing-instance.

Kind regards,
Truman



On 26/08/2008, at 7:48 PM, Steve Bertrand wrote:

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?

Thanks,

Steve