This scenario is a network with four routers in a square; each has a connection to a different transit provider with a full BGP table from each.
R1----R2 | | | | R3----R4
How do I calculate the (BGP) memory requirement for one of these routers? (not including IGP and LDP/RSVP etc)
In this example network all routers are Cisco 7301's with NPE-G1. Graphing the memory usage on them, they are all currently around the 500MB mark of used RAM, and the BGP table is approaching 500k prefixes (circa 470k at the time of writing). I know there is typically a margin of deviation here, but is there a rough way I can calculate how much memory a router needs if it is going to take a full BGP feed. It only needs to be rough, because if say 500k prefixes requires 500MBs, and 600k prefixes requires 600MBs of RAM, I'm not going to drop in a router that has exactly that much RAM, otherwise it has no growth room. So I'm after a rough method. Lets say I want to add a 5th router into this ring between R3 & R4, connected to another transit provider with a full BGP table feed; How do I work out how much RAM that router needs?