On 01/07/2010 15:37, Stuart Purdie wrote:
> So, here's a request for it. After some initial comparisons with Glasgow, Lancaster and Bristol, there might be something lurking in NAT configurations.
>
I've been having a look at it today since LHCb transfers started here again.
Quality does definitely drop as soon as SACK and DSACK are enabled, and a lot of
invalid SACK packets start showing up on the NAT box (as logged by an iptables
rule, '-p tcp -m tcp --tcp-flags ACK ACK --tcp-option 5 -m state --state INVALID
-j LOG --log-prefix "INVALID: " --log-level 6 --log-tcp-options'). Changing the
way those packets are handled didn't seem to make any difference. What sort of
configuration issues do you suspect?
I did find that there was a bug in conntrack in kernel versions prior to 2.6.26:
http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=84ebe1cdae56707b9aa1b40ae5aa7d817ba745f5
We're currently running 2.6.23 on our NAT box (it has 2.6.30 installed, but
hasn't been rebooted to use it yet) so that could be an issue here.
However, Lancaster are running 2.6.18-164.6.1.el5 which doesn't have the fix in
and they don't have problems, so that does suggest there's another factor at work.
Rob
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