Re: TCP/IP stack overloaded?

Linux Advanced Routing and Traffic Control

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Hi Ari,

You need to isolate the problem more, from you description, the
problem could come from anywhere. I would look at the number if system
interrupts, qdisc and class statistics and nic statistics provided by
ethtool -S in order to isolate the problem. You could also mention ram
utilisation and the kernel version running on the system.

Remy
On 12 February 2013 00:54, Ari Heitner <ari@xxxxxxx> wrote:
> We are having a strange intermittent problem on a natting firewall that's
> been loyally serving us for years, and the current theory is that our
> recent major connection upgrade (to 16/7 mbit, from about 7/1) plus the
> switch to voip phones, is periodically bogging down the machine, which is a
> little long in the tooth - a pIII-500.
>
> Symptom: seemingly randomly, up to a few times a day, the network
> connection just chokes for about 30 seconds. Pings and DNS still work ok,
> but http traffic and seemingly anything else TCP just stops. Wait a few
> seconds, and it starts again, processing the pending requests (i.e. the web
> page you were waiting for suddenly loads, without hitting refresh again)
> but playing havoc with voip phone calls. The behaviour seems to correlate
> with the network being busy, but generally the machine can handle
> throughput saturation with no problem, and does so regularly.
>
> My friend suggested a stress-test: making a vpn (pptp) to his network, and
> seeing if that makes the nat firewall box act up. Sure enough - make the
> connection, and start copying a file (at a very low throughput like 50
> kB/s) and load the network a little bit, and it freezes. And when the vpn
> connection is active, even without doing anything, stuff starts getting
> weird - the machine sometimes stops accepting incoming connections on port
> 22, and logmein.com sessions in progress will fail.
>
> But through all of this the machine shows no load, and the tc in place
> (wondershaper, modified slightly to prioritize traffic to and from the
> remote voip server - I can post the script and tc output if it would be
> useful) show no unusual amounts of packet droppage - which makes sense,
> since the issue isn't a bandwidth overload.
>
> How can I get stats on the "health" or load or anything of the tcp/ip
> stack? Am I even barking up the right tree here?
>
> Any and all suggestions would be appreciated.
>
>
> Cheers,
>
> Ari
>
> --
> Ari Heitner
> Director of Technology
> www.NCSY.ca - www.TorahHigh.org
> w: 905.761.6279 x223 m: 647.202.1998
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