[c-nsp] Peering between route reflectors

[Vitkovský Adam]

> Gert's got it, a network with a massive # of clients may justify hierarchical RRs
> although the design might be a throwback to the days of small boxes with
> minimal memory. Today's control plane only systems can scale to hundreds if
> not thousands of clients. Hierarchy might be useful if the second tier RRs are
> in the forwarding path and need to conserve resources for something other
> than BGP.
> 
> Just curious, anyone out there using hierarchical RRs?
> 
> Lee
> 

Yes you are right the complex combinations of topology-based and multi-planar address-based RR designs are the state of the art legacy from days where engineers had to fight back the lack of memory in routers while distributing millions of VPN prefixes around the globe. 
Though I think the topology-based RR models are still applicable even with modern gear. 
Would these be hierarchical RR designs? No, not really. 
So unless the partial-mesh between nodes in clusters becomes unmanageable in a particular region you don't need a RRs hierarchy. 

address-based RR = set of RRs distribute only a subset of all routes. 
topology-based RR = set of RRs serving a particular geographic area. 


adam