dns lookups lagging server

Steve steve at digitalbluesky.net
Sun Jan 8 10:49:07 PST 2006


I've been running FreeBSD 5.3 on an Intel Celeron server at home for about 
a year flawlessly.  The server is behind a linksys router on a Speakeasy 
DSL connection.  The server is used for internal network backups and do a 
small amount of web/email hosting.  Just yesterday afternoon however, when 
I tried to ssh into the box from the private side of the network, the 
connection timed out.  Several times.  Out of curiosity I tried to ftp to 
the box and that connection timed out as well.  Apache was running and the 
box still served webpages, but it was extremely slow - on the order of 
minutes to process and return even simple static pages.  The only thing 
that wasn't laggy and seemd to work okay was email and samba.

I hooked up a monitor and keyboard to the server and was able to log 
in.  top, ps and lsof commands didn't show anything out of the ordinary 
with the box and it seemed quiet normal.  I tried to establish an ssh 
session, which worked after a long delay.

So all the internet services setup on the box were running, just very slow, 
to the point where connections would timeout.

Eventually, I turned off dns lookup in sshd_config.  When I tried a ssh 
session after doing that, it worked right away.  I turned off dns lookup 
related commands in apache and proftpd and those services responded 
normally again (no significant lag or connection timeout errors).

So from the actions I took, it seems like there is a problem with the 
various services trying to do dns look ups on users who try to connect to 
the box somehow.  Since the problem started with no apparent involvement on 
my part (I had neither installed or uninstalled any applications, etc.), 
should I assume there is a dns server problem with my ISP?  The desktops 
here at home don't have a problem with dns themselves - it just seems to be 
the FreeBSD server.

What else should I be doing to diagnose the problem?

Steve Bopple

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