dhcpd performance?

Glenn Satchell Glenn.Satchell at uniq.com.au
Wed May 2 14:50:06 UTC 2007

>Date: Wed, 2 May 2007 10:16:09 -0400
>From: "Jiann-Ming Su" <sujiannming at gmail.com>
>To: dhcp-users at isc.org
>Subject: Re: dhcpd performance?
>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,

In the class definition there was an if statement to detect a
particular option that was only requested during the initial boot. So
we set a max-lease-time 10 in that section. Trouble is dhcpd hardwires
a 120 second lease time when offering an address. We changed the source
to move that back to 30 seconds.

>> 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.

No, we never came across that one. This was alcatel handsets, A4400.
The PABX was alcatel too, and ran a version of Linux which I thought
was pretty cool. Of course their 'customised' dhcp server supposedly
worked fine, except it was a hacked version of ISC dhcpd 2.0, so had
quite a few other limitations.

You can find it in the archives, 15 Dec 2004, "SUMMARY Alcatel A4400 IP
Phone and Auto Vlan Assignment".


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