Watching performance on a DHCP Server
blake at ispn.net
Tue Feb 12 19:49:55 UTC 2008
-------- Original Message --------
Subject: Re: Watching performance on a DHCP Server
From: sthaug at nethelp.no
To: dhcp-users at isc.org
Date: Tuesday, February 12, 2008 3:48:48 AM
>> 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 nethelp.no
Th numbers I'm quoting are performance figures from the dhcperf testing
tool. If your 100k users were to be down 24 hours (due to regional power
failure, massive server/network failure), how would your DHCP server
cope with 100K requests at once? This thread is not about 'normal'
conditions, it is about the extreme cases that administrators (at least
good ones) are expected to design for and accommodate ahead of time.
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