[DHCP] Re: Multiple subnets, wired/wireless

Ashley M. Kirchner ashley at pcraft.com
Thu Oct 1 15:46:02 UTC 2009

    First of all, my apologies for in a way "dropping the ball" on this 
one.  I posted my original question, received replies and simply got too 
busy with other projects and didn't reply back to this thread.  Thanks 
to both Niall and Alan for their replies as well.

Glenn Satchell wrote:
> First up you need to connect your dhcp server to the second network.
> You can do this directly through a second NIC, or via the first network
> through a router.
    It will be through a third NIC, though whether it's second, third, 
or nth shouldn't make any difference.

> Secondly you configure the subnet declaration in dhcpd.conf. This looks
> exactly the same whether it is a local subnet (like your first one) or
> a remote subnet using a DHCP relay.
> There is an example in the dhcp.conf man page, but essentially it will
> look something like this:
> # global options (eg dns servers, domain name and so on)
> option domain-name "example.com.au";
> option domain-name-servers server1.example.com.au, server2.example.com.au;
> default-lease-time 14400;
> # wired subnet
> subnet netmask {
> 	option routers;
> 	range;
> }
> # wireless subnet
> subnet netmask {
> 	option routers;
> 	range;
> 	default-lease-time 3600;
> }
    This is what I wasn't entirely sure about, mainly because we have 
several options set on our current subnet and I didn't quite understand 
how to separate them from this new subnet.  Somewhere I saw mention of a 
"shared-network" option and things started getting fuzzy.  So I 
appreciate your example above as that made things a lot clearer.

    There are still bits and pieces I have to figure out here.  For 
example, we allow our internal firewall to update the external DNS and 
thus have lines like:

option ip-forwarding off;
ddns-update-style interim;
ddns-domainname "int.pcraft.com";
ddns-updates on;
do-forward-updates on;
allow client-updates;

    There's a DHCP_UPDATER key being used for the updates.  How will 
this affect a second subnet?  Do I have to move these lines inside of 
the subnet{} statement?  Will it even work?  I don't know till I try it 
I guess.

    -- A

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