[c-nsp] Growing BGP tables

[Krzysztof Adamski]

On Thu, 25 Nov 2004, Bill Wichers wrote:

>
> > Maybe there are some Livingston engineers around who did BGP on the
> > Portmaster3 that can give some ideas on memory usage.
> >  From what I remember the PM3 was able to fit two full views (back
> > then about 100k routes each) into 32MB of RAM.
> >
> > The minimum amount of space needed to store 140k routes is 1.6MB (4
> > bytes for network, 4 bytes for netmask, 4 bytes for destination).
> > The overhead per route must be huge.
> >
> > K
>
> You are leaving out all the AS path / nexthop type info that BGP needs to
> be able to do intelligent things with the route table. There's a lot more
> in a multihomed router than just this->there type of stuff. I'm not sure
> it would be possible to calculate a "minimum" memory needed for some given
> number of routes, since you can't know exactly how much path info will
> need to be stored with each route. You should be able to get *close* on a
> large route table though by determining an average bytes/route which is
> easily done from the info given in 'show bgp sum' on a Cisco box.

I started with the bare minimum (the netmask can be shrunk down to 1 byte,
or 5 bits), I know you need lot more info, the AS path, MED, weight, local
pref, etc.
But this discussion started about memory requirement of a VIP, how much of
the extra info is needed on the VIP?

K