dhcpd performance?

Jiann-Ming Su sujiannming at gmail.com
Wed May 2 14:16:09 UTC 2007

On 5/2/07, Glenn Satchell <Glenn.Satchell at uniq.com.au> wrote:
> I have run dhcp in failover mode on two low end Sun boxes (Netra T1).
> 3500 PCs, 4500 Phones. When the PABX gets rebooted all the phones reset
> simultaneously. This was a rare event (maybe once/year) and was always
> scheduled for out of hours when possible.
> The phones were spread across 6 or 7 vlans in different locations. So
> about 1200-1500 phones in the largest office.
> In our particular situation the phones requested an IP address on the
> PC vlan, then after receiving an offer reset to the phone vlan. Our
> bottle neck was that we only had 200 or so free IP adresses in the
> initial vlan, so it would take up to 2 minutes for a lease to expire
> after the initial offer before it could be re-offered. We tuned the
> timeout value back to 30 seconds and found all the phones would be
> sorted out within a couple of minutes.

Yeah, this sounds like our deployment on size and scale.  I'm assuming
you change the lease to 30 seconds just for these reboot cycles,

> Of course the PABX then struggled as all the phones downloaded
> configuration files as the second part of the boot.

Yeah, I've been asking various tftp server mailing lists similar questions.

> This was a rare event, and had we just used addresses on the default
> vlan would have been fixed much more quickly.

We solved the free lease problem by multinetting a private subnet on
the native/PC vlan, and using the "allow members of voip-phones"
directive in the pool definition, where "voip-phones" is defined by
class and subclass.

> In normal circumstances we used a 1 week lease for the phones and the
> trickle of renewals was never a problem.

Did you guys run into a scenario where the phones wouldn't accept
lease times less than 24 hours?  This was really annoying when using
the ISC DHCP failover configuration because of the MCLT.

Jiann-Ming Su
"I have to decide between two equally frightening options.
 If I wanted to do that, I'd vote." --Duckman
"The system's broke, Hank.  The election baby has peed in
the bath water.  You got to throw 'em both out."  --Dale Gribble

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