[PLUG] Behavior of a heavily loaded server

Derek Loree derek at infotects.com
Thu Aug 1 18:39:23 UTC 2002


Hi Steve,

Thanks for the information.

On Mon, 2002-07-29 at 17:22, Steve Bonds wrote:
> On 29 Jul 2002, Derek Loree derek at infotects.com wrote:
> 
> > Over the weekend, we had the opportunity to have our servers
> > thoroughly pounded (rumor is almost 1/4 million users in less than an
> > hour).  Needless to say we had a hard time keeping things going
> > (though they did keep going).
> > 
> > Questions that arise after the fact:
> > 
> > Is there a limit to the number of connections a Cisco router can deal
> > with (even if the pipe is not full of packets)?  I'm wondering if some
> > of the problems we had were upstream.
> 
> I'll let some of the Cisco experts comment, but the short answer is yes.

Is this memory related or OS related (ie. hardware or software)?
> 
> > What exactly happens when the syslog says "TCP: drop open request from
> > xxx.xxx.xxx.xxx/xxxxx"?  Is this a connection that timed out (hung in
> > there for the 30 secs that apache gives it), or was it dropped as soon
> > as it was connected (there was a one minute period where I had close
> > to 1000 of these)?
> 
> This is a result of the TCP syn cookies code kicking in and dropping TCP
> connections.  Look at tcp_ipv4.c for details.  ;-)

That was a good read, I don't understand much of the code, but it was
easy to see what the code does to keep the server from crashing.

Thanks again.

Derek






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