Watching performance on a DHCP Server

John Hascall john at
Sat Feb 16 22:45:49 UTC 2008

> At these volumes/rates, are people syslogging DHCP traffic to disk?

We are.  However, our platform (NetBSD) does not fsync after
non-kernel calls to syslog.  If you are using a platform where
syslog (e.g., [at least some variants of] Linux) fsync's by
default you might wish to disable that as it can become a
bottleneck (look for "-file" in "man syslog.conf").

Also, our syslog is on a different disk (a RAID 0)
than our leases (a RAID 1).


> Frank
> -----Original Message-----
> From: dhcp-users-bounce at [mailto:dhcp-users-bounce at] On Behalf
> Of sthaug at
> Sent: Tuesday, February 12, 2008 3:49 AM
> To: dhcp-users at
> Subject: Re: Watching performance on a DHCP Server
> > You may want to review the thread from the beginning. My network
> > currently has 10,000+ DHCP clients (and I plan on accommodating double
> > that within the lifetime of this server). I have a beefy server (4x
> > 3.0GHz Xeon, 2x 15k RAID1) and it was only able to reliably handle 10 to
> > 20 4-way discover handshakes a second, 2-way handshakes were maybe
> > double or triple those numbers. When pounded by DHCP requests, it's
> > possible that even less are processed in a timely manner due to
> > collisions, timeouts, etc.
> I really don't understand the numbers people are quoting here. We use
> a Dell 1850 with one 3.2 GHz CPU, one Gig of memory and two SCSI disks
> in battery backed hardware RAID 1. We use this to serve 100K customers
> with 24 hour leases. No problems whatsoever, and we feel we have plenty
> of room to grow.
> (Some calculations: Clients are expected to renew after half the lease
> time has passed. So we can expect 100.000 renewals in 43200 seconds, or
> a little over 2 renewals per second. Monitoring the actual DHCP traffic
> on the server shows numbers which are consistent with this. We have run
> with considerably shorter lease times - down to one hour in connection
> with planned network reconfigurations - and again the increased DHCP
> traffic has been no problem whatsoever.)
> Steinar Haug, Nethelp consulting, sthaug at

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