North American Network Operators Group

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Re: cpu needed to NAT 45mbs

  • From: Deepak Jain
  • Date: Thu Nov 08 18:18:01 2007

	A second CPU or core will help tremendously. We used to use single-CPU
boxes for this and we noticed that traffic sometimes stalls when the machine
has to do some task other than NATting, such as expiring idle flows. Having
a second CPU or core will help keep latency much more uniform.

	We have a few dual 3.2Ghz Xeon boxes (not the ones based on Core, the older
ones) that NAT/FW across two GE interfaces. They do quite well up to about
300Mb/s, then we start to see issues. We believe the issues are due to
overloading the NB-SB link. A more modern mobo probably wouldn't have this

Since we are talking about PC Routers... 300Mb/s is a limitation we've seen before... especially related to Interrupts overwhelming the system. Modern ethernet cards (non-interrupt based) and a modern OS with support for all of their offloading and zero-copy functions will improve this greatly.

Current FreeBSD is signficantly faster than current Linux implementations for this kind of work.

But (as I told the OP privately) 45mb/s is a joke and doesn't really need anything more than a 400mhz P-II with two Intel EtherExpress cards and 1GB of RAM. Even for 4,000 downstream connections. A few $200-$300 L3 switches can do this just as well.

Deepak Jain