BGP, ebgp-multihop and multiple peers

Wed Aug 27 01:40:05 UTC 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
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