Same Host on two ip pool?

[Glenn Satchell]

>Date: Fri, 10 Oct 2008 18:50:28 -0430
>From: "Juan C. Crespo R." <jcrespo at ifxnw.com.ve>
>To: dhcp-users at isc.org
>CC: dhcp-users digest users <ecartis at isc.org>
>Subject: Re: Same Host on two ip pool?
>
>
>> ------------------------------
>>
>> Date: Thu, 9 Oct 2008 07:41:43 +0100
>> From: Simon Hobson <dhcp1 at thehobsons.co.uk>
>> Subject: Re: Same Host on two ip pool?
>>
>> Juan C. Crespo R. wrote:
>>   
>>
>> Do you mean - you want a client to be able to get an address on any 
>> of several networks it can connect to ? Yes, it just works 
>> automagically as long as your network is set up right.
>>   
>Could you send me an example of this one? Thanks :)


man dhcpd.conf, look for fixed-address

     If it is desirable to be able to boot a DHCP or BOOTP client
     on  more than one subnet with fixed addresses, more than one
     address may be specified in the  fixed-address  declaration,
     or  more  than  one host statement may be specified matching
     the same client.
 ...
     The fixed-address declaration

       fixed-address address [, address ... ];

       The fixed-address declaration is used  to  assign  one  or
       more  fixed  IP  addresses  to  a  client.  It should only
       appear in a host declaration.  If more than one address is
       supplied,  then when the client boots, it will be assigned
       the address that corresponds to the network on which it is
       booting.   If  none  of the addresses in the fixed-address
       statement are valid for the network to which the client is
       connected, that client will not match the host declaration
       containing that fixed-address declaration.   Each  address
       in  the  fixed-address  declaration should be either an IP
       address or a domain name that resolves to one or  more  IP
       addresses.

host xxx {
  hardware ethernet c:0:f:f:e:e;
  fixed-address 192.168.1.2, 192.168.2,42, ...;
}

When the request comes in, if the subnet it came from matches one of
the fixed addresses, then it will be assigned that address.

The only trick is that this host will now be "known", so if you deny
known-clients in a pool it won't be able to dynamically get an address.
Workaround for that is to create another host entry - different name,
same ethernet - and leave out the fixed-address statement.

(The entries above are so people might find this information when they
search the archives.)

regards,
-glenn