dns lookups lagging server
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?
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