Allocating a fixed IP address with Dynamic DHCP

[Simon Hobson]

Quadstone Ltd wrote:

>We are running Bind 9.2.3, ISC DHCP 3.0.1 and Samba 2.2.8a (as a domain
>controller/WINS server).
>We have laptops with 2 or 3 network interfaces - builtin ethernet, docking
>port and Wireless card.
>If we allocate a separate IP address to each interface we get problems
>with WINS as it usually doesn't change the IP address in the Samba wins.dat
>file if you say undock a laptop and start using the builtin network card.
>One suggestion is to use Dynamic DNS via DHCP.  Is it possible to use this
>to allocate fixed IP addresses on certain networks.  I.e. a laptop is
>always allocated the same IP address whatever network interface is being used?

This is a DHCP question, so I suggest any further traffic be directed 
to the dhcp-server list (to which you can subscribe at 
http://www.isc.org/).

You would need to create three separate host statements, all using 
the same fixed address :

host laptop-lan {
   hardware ethernet xx:xx:xx:xx:xx:xx ;
   fixed-address a.b.c.d ;
}
host laptop-dock {
   hardware ethernet yy:yy:yy:yy:yy:yy ;
   fixed-address a.b.c.d ;
}
host laptop-wlan {
   hardware ethernet zz:zz:zz:zz:zz:zz ;
   fixed-address a.b.c.d ;
}

By default however, fixed-address leases will not result in a ddns 
update - but in this case you would be better doing a manual DNS 
entry anyway.

Be aware that the dhcp server will quite happily lease out the same 
address to all three interfaces at the same time, which could cause 
problems if the laptop were connected by more than one at a time 
(dock+wlan for example).

Simon

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Simon Hobson, Technology Specialist
Colony Gift Corporation Limited
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