ipv4 connection problems

Peter Avalos pavalos at theshell.com
Sat Mar 5 21:16:51 PST 2005

On Sat, Mar 05, 2005 at 06:37:48PM -0800, Matthew Dillon wrote:
> :Over the past few weeks I've been having a problem with Apache not
> :responding to port it's listening on.  After some investigation, I
> :was able to determine that it was only happening on ipv4.  IPv6 was
> :working just fine.  If I restarted the server, everything would be fine
> :for about an hour or so (depending on traffic), and then it would
> :start up again.  I figured this was an Apache problem, since it was
> :only happening with my web server.
> :
> :Today, I was stressing out my ftp server (the vanilla base version),
> :and I saw that it was doing the same thing my web server was doing:
> :
> :box:~% telnet -4 theshell.com 21
> :Trying
> :telnet: connect to address Operation timed out
> :telnet: Unable to connect to remote host
> :
> :And without doing anything...
> :
> :box:~% telnet -4 theshell.com 21
> :Trying
> :Connected to theshell.com.
> :Escape character is '^]'.
> :220 box.theshell.com FTP server (Version 6.00LS) ready.
> :quit
> :221 Goodbye.
> :Connection closed by foreign host.
> :
> :Note:  This is not a network connectivity issue since those telnets
> :are on the same box (box is
> :
> :Again, ipv6 seems to work just fine.  Other than this, I don't really
> :know what other information I can provide that can help in finding
> :where the problem is.  Any thoughts?
> :
> :Peter
>     You need to do a bit more investigation.  Use tcpdump on the server
>     to see if the machine is even *receiving* the connection attempt that
>     is timing out on you, and check that your Apache has not hit its 
>     programmed simultanious connection limit, controlled by its config
>     file (there's an apachectl command that will do that).

In the above test I was connecting to the ftp port on the machine.  I'm
confident this has nothing to do with Apache now.  I'll have to see
about running tcpdump and see what's going on.  I was assuming that since
I was running telnet directly from the box that the server is running,
it's not a network connectivity problem.  I have a feeling that the socket
is not getting the connection attempts for some reason.  I'm curious if
anyone else is seeing this behavior.

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