ip_input - chksum - why is it done so early in ip_input?

[Ruslan Ermilov]

On Sat, Jan 17, 2004 at 12:50:04AM +0100, Sten Daniel S?rsdal wrote:
> 
> Apologies for the cross-post, i wasnt sure if this was hackers or net material.
> 
> I've often wondered why ip checksumming is done on every incoming 
> packet and not only on the packets that need to be delivered locally.
> It looks like a very expensive way of doing it, especially on high
> PPS. Basically all hosts do checksumming so why not just pass the bad
> packet on, making the forward process alot cheaper (cpu wise)?
> 
> I ran some tests (unable to disclose results) by removing it completely
> and it seems to make a noticable impact on the performance.
> Especially on for example gaming services where there is a high PPS versus
> actual data.
> 
> Besides that i'd like to add that FreeBSD has the fastest forwarding engine
> i've seen on any free OS. It's in my opinion a very suitable OS for 
> routing/forwarding.
> 
Have you tried ``sysctl net.inet.ip.fastforwarding=1''?
It's documented in the inet(4) manpage.


Cheers,
-- 
Ruslan Ermilov
FreeBSD committer
ru at FreeBSD.org
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