Multiple subnets with relays
dhcp1 at thehobsons.co.uk
Mon Jan 19 08:03:07 UTC 2009
Jessica Meyer wrote:
>I have a question about configuring DHCPD to answer requests according
>the value of the "DHCP relay" option. I have tried to find the
>information on the internet as well in the manpage, but could not find
>what I was looking for.
>I have to set up a quite complex environment (at least for me). I have
>already compiled the latest version of DHCPD on a debian machine and
>configured it so that I have three address pools.
>Now what I need is the following:
> - DHCPD gets a request from a client.
> - DHCPD looks at the relay agent option.
> - If the relay agent IP is 10.0.0.1, give out an IP address from
> 10.1.0.0/16 or 10.2.0.0/16, but not from any other address pool.
> - If the relay agent IP is 192.168.0.1, give out an IP address from
>I hope my explanation is easy to understand... I already configured a
>shared-network for the 10.x.0.0/16 networks, but I am not sure if this
>is the right way.
Congratulations, your config is just what you need (apart from adding
a few options like routers etc). The rest is automagic - the server
spots that the GIAddr (Gateway Interface Address) field is filled in
and uses it to determine which subnet (or shared network) the client
is connected to.
It's a common source of confusion for new users, though
shared-network (which you've got right) is usually even more
>Here is my configuration so far (relevant parts):
> server-identifier 192.168.0.2;
> subnet 192.168.0.0 netmask 255.255.255.0
> option subnet-mask 255.255.255.0;
> range 192.168.0.3 192.168.0.254;
> default-lease-time 36000;
> max-lease-time 36000;
> shared-network RELAY1
> subnet 10.1.0.0 netmask 255.255.0.0
> range 10.1.0.2 10.1.254.254;
> subnet 10.2.0.0 netmask 255.255.0.0
> range 10.2.0.2 10.2.254.254;
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