I'm hunting for some presentations or papers on what I've seen called a "peering module", using a router, a L2 switch, and a router in series, rather than a single router. Unfortunately, I can't remember where I saw the detailed description, and I haven't been able to find it in the NANOG archives.
IIRC, the rationale was to spread filtering and rate limiting over a set of processors, also to keep the configuations more manageable.
Does anyone have any pointers to detail? I've seen the topology, but not a detailed discussion, in a couple of Cisco presentations.