>>>> My web server's response time for http requests skyrockets every >>>> weekday between about 9am and 5pm. I've gone over my munin graphs and >>>> the only one that really correlates well with the slowdown is "TCP >>>> Queuing". It looks like I normally have about 400 packets per second >>>> graphed as "direct copy from queue" in munin throughout the day, but 2 >>>> to 3.5 times that many are periodically graphed during work hours. I >>>> don't see the same pattern at all from the graph of all traffic on my >>>> network interface which actually peaks over the weekend. TCP Queuing >>>> doesn't rise above 400 packets per second all weekend. This is >>>> consistent week after week. >>>> >>>> My two employees come into work during the hours in question, and they >>>> certainly make frequent requests of the web server while at work, but >>>> if their volume of requests were the cause of the problem then that >>>> would be reflected in the graph of web server requests but it is not. >>>> I do run a small MTU on the systems at work due to the config of the >>>> modem/router we have there. >>>> >>>> Is this a recognizable problem to anyone? >>> >>> >>> I'm in the midst of this. Are there certain attacks I should check for? >> >> >> It looks like the TCP Queuing spike itself was due to imapproxy which >> I've now disabled. I'll post more info as I gather it. > > > imapproxy was clearly affecting the TCP Queuing graph in munin but I > still ended up with a massive TCP Queuing spike today and > corresponding http response time issues long after I disabled > imapproxy. Graph attached. I'm puzzled.
I just remembered that our AT&T modem/router does not respond to pings. My solution is to move PPPoE off of that device and onto my Gentoo router so that pings pass through the AT&T device to the Gentoo router but I haven't done that yet as I want to be on-site for it. Could that behavior somehow be contributing to this problem? There does seem to be a clear correlation between user activity at that location and the bad server behavior. - Grant