DHCP/UDP performance tuning..

Frank Bulk frnkblk at iname.com
Wed Mar 28 03:10:35 UTC 2007

What about writing the dhcpd.leases file to a virtual disk or flash?


-----Original Message-----
From: dhcp-users-bounce at isc.org [mailto:dhcp-users-bounce at isc.org] On Behalf
Of Cory Meyer
Sent: Tuesday, March 27, 2007 11:31 AM
To: dhcp-users at isc.org
Subject: DHCP/UDP performance tuning..

Does anyone have any suggestions on performance tuning a DHCP server?
Basically the problem that I'm running into is that my server isn't able to
handle any more than 20 DHCP requests per second..  Any more requests than
that and basically my UDP buffers fill up and not all of the requests are
answered.  By the wonders of UDP this turns into a snowball effect and the
numbers of DHCP requests per second goes up since the clients aren't seeing
all of the responses.

I've attempted to change the UDP buffers from a default of 128k to 1Mb and
8Mb with no changes in the outcome.

Mathematically I'm figuring that the server should be getting about 24
requests per second. This is figured out with 47110 current leases with a
7200 sec default lease time with a 14400 max-lease.  Additionally I have 531
leases that have a 30 sec lease time.  Since we use a MAC address
registration system the pool with the 30 sec leases are for unregistered MAC

In my testing with TCPDump over a 72 second capture it was getting 45
requests per sec and the replies were at 33 per second during the same

Here is a quick overview of what I'm running with:

RedHat Enterprise 3.0
HP DL380 G3 server with Dual Xeon 2.8Ghz proc and 4 Gb RAM.
Raid5 setup includes 3 32gig UltraSCSI drive.

Current Sysctl Settings:
net.core.wmem_default = 65535
net.core.wmem_max = 131071
net.core.rmem_default = 131071
net.core.rmem_max = 131071

Any responses would be greatly appreciated.


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