Multiple next-servers ?

[Glenn Satchell]

>From: Richard Offer <offer at fastscale.com>
>To: "dhcp-users at isc.org" <dhcp-users at isc.org>
>Date: Mon, 3 Sep 2007 17:40:21 -0700
>Subject: Multiple next-servers  ?
>
>Is it possible to list multiple next-servers for use in a HA environment ?
>
>
>The docs seem ambiguous neither including or precluding it ?
>
>
>Richard.

If you go to RFC2131 it's not ambiguous. There is one 4 byte field
available for siaddr (which is what next-server sets).

In dhcpd.conf man page, there is no mention that more than one address
can be supplied:

     The next-server statement

       next-server server-name;

       The next-server statement is  used  to  specify  the  host
       address  of  the  server  from which the initial boot file
       (specified in the filename statement)  is  to  be  loaded.
       Server-name  should  be  a  numeric IP address or a domain
       name.

Here is an example, from dhcp-options man page, that accepts multiple
servers.

     option domain-name-servers ip-address [, ip-address... ];


However, you can define different a next-server in different scopes if
that helps.

One model is that if you use failover, then each dhcp server refers to
itself as the next-server. That way if the other server is down it won't
try and direct clients to that system.

Alternatively you could use a floating IP address that gets moved
between servers - this is the linux-ha model (and others).

regards,
-glenn