independent servers on same subnet

[Glenn Satchell]

>Date: Fri, 11 Jul 2008 13:26:12 -0400
>From: "Japhy Bartlett" <japhy at pearachute.com>
>To: dhcp-users at isc.org
>Subject: Re: independent servers on same subnet
>
>The way to "decide" is in the routing, no?

No. dhcp uses broadcasts for DHCPDISCOVER packets, so if the two
servers are on the same subnet or vlan then both will see all
broadcasts. These are done as layer 2 broadcasts with destination mac
set to ff:ff:ff:ff:ff:ff.

Each dhcp server needs to be ocnfigured in some way to ignore requests
which it shouldn't server. With dhcpd the easiest way is to use classes
based onthe mac address or a substring of it (eg first three bytes) or
to use hosts statements which also matchon mac address (hardware
ethernet ......).

Of course the tiny dhcp server needs to also ignore hosts so they don't
get it's default values.

Probably the tiny dhcp server should be turned off and it's
configuration merged into dhcpd's config.

regards,
-glenn

>Why not have the tiny dhcpd do NAT for the department?
>
>On Fri, Jul 11, 2008 at 8:27 AM, Carl Karsten <carl at personnelware.com> wrote:
>> Friend works in an IT dept is describing an upcoming migration passed this
>> on:
>>
>>> the guy was telling me that the department already had their own tiny DHCP
>>> server running, and now the bigger DHCP server is handing out IP addresses
>>> even to the ones they'd rather keep on their tiny DHCP server.  If you've
>>> got
>>> 2 DHCP servers, there's no way, as far as we can tell to "decide" which
>>> DHCP
>>> server any machine talks to first.
>>
>> Not that there is any good reason to do this, but maybe if I pass back what
>> it would take to do it right they might realize it isn't a good idea.
>>
>> So, what can be done to run a 2nd dhcp server?
>>
>> Things that come to mind:
>>  - both servers need mac addresses to respond to or ignore.
>>  - clients send a client ID or something, one responds if it sees it, one
>> ignores it if it sees it.
>>
>> Carl K
>>
>>
>>
>>
>>
>