BGP, ebgp-multihop and multiple peers
truman at suspicious.org
Tue Aug 26 20:40:05 CDT 2008
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
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.
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?
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