Number of interfaces limitation

Glenn Satchell Glenn.Satchell at
Wed Jul 19 11:54:14 UTC 2006

>Date: Wed, 19 Jul 2006 13:04:35 +0200
>From: Shane Kerr <Shane_Kerr at>
>To: dhcp-users at
>Subject: Re: Number of interfaces limitation
>Hash: SHA1
>Ivan V. Borodin wrote:
>> Hello there,
>> Does anybody know something about total number of interfaces which dhcpd
>> can listen? What about 2048 interfaces, for example?
>As far as I know, there is no built-in hard limitation on the number of
>interfaces which the ISC DHCP server can support.
>However, the server uses the select() call to check for packets. This
>function has a limited number of file descriptors it supports. In Linux,
>for example, it only allows 1024. The DHCP server requires 2 file
>descriptors per interface, plus a few extras for logging, writing
>leases, and the like. So the practical limit is probably around 500
>I'm curious what environment you have that needs more than a few interfaces!
>- --

It used to be the case a few years ago that there was an internal array
of a fixed size that limited the number of interfaces. I haven't heard
of this as a problem for a long time, so perhaps it was changed to be
dynamically allocated?


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