ipv4 connection problems

Matthew Dillon dillon at apollo.backplane.com
Mon Mar 14 16:35:32 PST 2005

    Peter.  I did some webbench tests to try to reproduce the problem, and
    I found two limitations that might have something to do with it.  I 
    would like you to check these two things while your machine is not responding
    to apache requests.

    If it turns out to be one of these two things, I don't think your issue is
    related to the firefox or opera issue.

    You could be:

    (1) Running out of sockets.
    (2) Running out of tcp ports.

    (1) Running out of sockets.   Any server that accepts connections will wind
	up with the socket in a TIME_WAIT state for 2 minutes after the connection

	If your kern.ipc.maxsockets is, say, 5000, then 5000 / 120 seconds ==
	only 33 connections per second before you run out of sockets.

    (2) Running out of tcp ports.  If you are getting a lot of connections from
	the SAME IP address, the originating machine (the client you were using
	to test connections to your ftp server in this case) may run out of TCP
	ports or may start reusing ports that are still in TIME_WAIT on the 
	target machine. 

	2 minutes to timeout it would only take 33 connections per second to run
	out of ports.  But ONLY if all the connections are coming from the same IP
	address (since the limitation is based on the {ipaddress,port} tuple, not
	just the {port}).

    How do you tell?  When you hit this situation, do this:

    sysctl net.inet.ip.portrange
    sysctl kern.ipc.maxsockets
    netstat -tn | wc -l
    netstat -tn | fgrep TIME_WAIT | wc -l
    netstat -m

    And that should tell you (and us) what is going on.

    If that turns out to be the case, then it probably is not related to the
    Opera/FireFox delay issue.


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