Software router state of the art

William Herrin herrin-nanog at
Sat Jul 26 13:35:59 UTC 2008

On Sat, Jul 26, 2008 at 7:41 AM, Dorn Hetzel <dhetzel at> wrote:
> Ok, it's probably a stupid question, but given the relative ease of putting
> 4gb+ ram on a 64bit platform,
> could packet per second performance be improved by brute forcing the route
> lookup as an array of 1 byte destination interface indexes for a contiguous
> swath of /32's from bottom to top?
> Route updates would be a little ugly, 2^24 bytes to rewrite for a /8, but
> forwarding lookups out to be a single indexed read ?


In theory with about 6 gigs of ram for the IPv4 FIB, sure. But:

You're significantly multiplying the likelihood of a cache miss when
performing a lookup. You can do a fair amount of tree traversal in
cache for the price of one miss.

You're a tad shy on ram to try this with IPv6.

Bill Herrin

William D. Herrin ................ herrin at bill at
3005 Crane Dr. ...................... Web: <>
Falls Church, VA 22042-3004

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