DHCP Server not able to handle the Traffic
dhcp1 at thehobsons.co.uk
Sun Apr 26 08:58:11 UTC 2009
Agarwal Vivek-RNGB36 wrote:
>Iam using ISC-DHCP-3.0.5 installed on RHEL5
>When I take a tcpdump on the DHCP Interface; I saw around 1000 DHCP
>Discovers at the interface but when I see /var/log/messages I can
>see only around 500 DHCP DISCOVERs over there.
>Can anyone help me in debugging that where are the discovers being
>lost and how can I check resolve that
Need more information than that ! Over what period is this - 1000
messages in one second, or 100 messages over one day, or something in
The server does have a limited response rate, and if you exceed that
then buffers will fill and packets will get discarded. The limit is
highly dependent on several factors which get discussed fairly
regularly on this list - usually in response to questions of the form
"how many clients will the server support" or "will the server
support X clients".
There are several things you can do to improve performance. The thing
to remember is that the server is single threaded and so anything
that slows it down will restrict it's performance.
Logging. It logs stuff quite frequently, so first thing to do is
configure your logging to be asynchronous - otherwise the DHCP server
must wait while each log message is written to disk. That's in your
syslog configuration, and in the 'old fashioned' original syslog it's
a case of preceding a log file name with a '-'. For newer syslog
variants, check the manuals.
DNS. Depending on your config, the DNS service could be getting
updated. Make sure that this is working correctly, and make sure you
aren't doing excessive updates (eg by setting "update-static-leases
true" when you have lots of static address assignments.)
Lease file storage. The server is required (as in absolute MUST) to
write all leases to permanent storage before offering them to
clients. Make sure the leases file is on a disk with good performance
and which isn't too busy from other activities. In extreme, some
people have put this on battery-backed ram disks etc.
And the obvious one, can you reduce the query rate from clients ? Do
you have short lease times ? If so, then increasing them will reduce
the query rate.
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