Alias IP

[Glenn Satchell]

>X-Original-To: dhcp-users at webster.isc.org
>Date: Mon, 20 Nov 2006 15:11:34 +0100
>From: Zachár Balázs <zachar at direkt-kfki.hu>
>To: dhcp-users at isc.org
>Subject: Alias IP
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>X-original-sender: zachar at direkt-kfki.hu
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>Hello @list!
>
>I have the following problem:
>
>active/passive cluster with one virtual IP address...
>
>A node real IP: 192.168.1.2
>B node real IP: 192.168.1.3
>virtual common IP: 192.168.1.5
>
>So I have an alias IP address in my interface. The dhcp requests come to 
>the alias IP (192.168.1.5) but the offers going out on the real 
>interface IP (e.g. 192.168.1.2).
>Maybe the problem:
>If I give an IP with my real interface, and before the client would like 
>to renew his IP address the cluster is failover, the dhcpd's IP address 
>will change... But if I send the offers trough the alias interface, If 
>the cluster fail over the IP address is still the same (the virtual IP)...
>
>Can I send the offers with my alias interface?

You might be able to use local-address,however there are some side effects.

  local-address 192.168.1.5;
  
man dhcpd.conf
...
       local-address address;

       This statement causes the DHCP server to listen  for  DHCP
       requests  sent  to  the  specified  address,  rather  than
       requests sent to all addresses.   Since  serving  directly
       attached DHCP clients implies that the server must respond
       to requests sent to the all-ones IP address,  this  option
       cannot  be  used  if  clients  are  on  directly  attached
       networks...it is only realistically useful  for  a  server
       whose  only  clients are reached via unicasts, such as via
       DHCP relay agents.

       Note:  This statement is only effective if the server  was
       compiled using the USE_SOCKETS #define statement, which is
       default on a small number of operating systems,  and  must
       be  explicitly chosen at compile-time for all others.  You
       can be sure if your server is compiled with USE_SOCKETS if
       you see lines of this format at startup:

        Listening on Socket/eth0

       Note also that since this bind()s all DHCP sockets to  the
       specified  address, that only one address may be supported
       in a daemon at a given time.

regards,
-glenn