Re: [squid-users] Bad TCP Checksums/Slow HTTPS connections

Hi,

Matus UHLAR - fantomas wrote:
> On 02.05.06 01:48, Sketch wrote:
>> Running tcpdump on the hosts that squid is running on shows the bad
>> checksum on outgoing squid packets. This means that the problem is
>> not a network switch/hardware, as the packet is built in kernel space,
>> and then determined to be bad before it ever hits the network
>> interface.
>
> the packets are propbablby OK, but the kernel probably uses checksumming
> capability of your network card(s), as many cards support this and it takes
> some load off the CPU.
>
> This is probably not a problem at all.

This is known as Checksum offloading. I once thought I had serious
problems on a Windows box... well I did, it was running Windows, but
every packet that went out had the wrong checksum, when running Ethereal
on the machine in question. Monitoring it at the network level showed
that the packets were OK and were obviously subject to checksum
offloading. In theory the packet should go to the NIC with a 0 checksum
and the NIC should fill in the blanks.

HTH,

Neil.

-- 
Neil Hillard                    hillardn@whl.co.uk
Westland Helicopters Ltd.       http://www.whl.co.uk/
Disclaimer: This message does not necessarily reflect the
             views of Westland Helicopters Ltd.