cpu needed to NAT 45mbs

Joe Greco jgreco at ns.sol.net
Thu Nov 8 20:31:54 UTC 2007

> I do the networking in my house, and hang out with guys that do networking in 
> small offices that have a few T1s.   Now I am talking to people about a DS3 
> connection for 500 laptops*, and I am bing told "a p4 linux box with 2 nics 
> doing NAT will not be able to handle the load."   I am not really qualified to 
> say one way or the other.  I bet someone here is.

So, are they Microsoft fans, or Cisco fans, or ______ fans?  For any of
the above, you can make the corresponding product fail too.  :-)

The usual rules for PC's-as-routers apply.  You can find extensive
discussions of this on lists such as the Quagga list (despite the list
being intended for routing _protocols_ rather than routing platforms) and
the Soekris (embedded PC) lists.


1) Small packet traffic is harder than large packet traffic,

2) Good network cards and competent OS configuration will help extensively,

3) The more firewall rules, the slower things will tend to be (highly

4) In the case of NAT, it would seem to layer some additional delays on top
   of #3.

We've successfully used a carefully designed FreeBSD machine (PIII-850,
dual fxp) as a load balancer in the past, which shares quite a few
similarities to a NAT device.  The great upside is complete transparency
as to what's happening and why, and the ability to affect this as desired.
I don't know how close we ran to 100Mbps, but I know we exceeded 45.

With sufficient speed, you can make up for many sins, including a
relatively naive implementation.  With that in mind, I'd guess that you 
are more likely to be successful than not.  The downside is that if it
doesn't work out, you can recycle that PC into a more traditional role.

... JG
Joe Greco - sol.net Network Services - Milwaukee, WI - http://www.sol.net
"We call it the 'one bite at the apple' rule. Give me one chance [and] then I
won't contact you again." - Direct Marketing Ass'n position on e-mail spam(CNN)
With 24 million small businesses in the US alone, that's way too many apples.

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