I'm looking for some guidance in sizing Cisco routers for different levels of BGP support. I'm aware that it requires 1 GB of RAM to handle the full BGP routing table, but the processing required to maintain neighbors/sessions, etc., would be too much for a 1941 ISR, for example. I'd like recommended solutions for the following scenarios:
1) A router that will be dual-homed to two different ISP's (same speed lnks - let's say 100-Mb each), and will be maintaining a full routing table to choose the best path based on BGP path attributes. So, in this case, the router will not be offering Internet transit services.
2) Same router, but it will only be storing a select number of Internet routes (for key sites/businesses - let's say 1,000 routes.) Still, no transit traffic.
3) Lastly, an ISP router maintaining full Internet routing table (322K routes as of today), and three OC3 connections to other ISP neighbors.
Thank you – as always, supporting links/reference documentation is appreciated.