incomming DHCPDISCOVER requests buffer

[Glenn Satchell]

>Subject: incomming DHCPDISCOVER requests buffer
>From: fadey <fadey at scancom.es>
>To: dhcp-users at isc.org
>Date: Mon, 21 Apr 2008 13:18:07 +0200
>
>Hi, everyone
>
>I was wondering what happens when there are too many dhcp requests
>comming? How many per second does one need to cause a DOS? Is there some
>sort of a buffer inside dhcpd that queues the incomming requests? Is (if
>there is one) it's size configurable?
>
>Thanks in advance
>

As the requests are UDP, it is quite ok for the server IP stack to just
drop the packets if there are too many for the UDP layer to handle.
dhcpd doesn't buffer these up, but rather handles them one by one. A
well behaved client should resend the request if it doesn't get an
answer soon enough.

Having said that there have been recent posts with servers handling
more than 100,000 clients. Of course the incoming rate depends things
such as lease time, how often clients are re-started, and so on, but it
indicates that most server hardware can handle a fairly high request
rate.

There have been a couple of posts this year relating to a dhcp client
test system that can simulate client requests at various rates. If
you're concerned about performance, then it may be worthwhile to do
some benchmarking against your servers and see how they behave under
high load.

regards,
-glenn