matching on giaddr field

[fadey]

Thanks a lot.

> On Wed, Jul 23, 2008 at 01:32:26PM +0200, fadey wrote:
> > I have varios cisco routers that support dhcp relay. I'd like to use a
> > single dhcpd to serve IPs to all devices behind those routers. The
> > problem is that devices from a specific router have to get the IPs from
> > specific range. Is there a way to do it with ISC dhcpd?
> > 
> > For now, the only solution I see is keep adding a separate network card
> > for every IP range I have to serve and creating a "shared network" for
> > every range. However this doesn't scale well (I might run out of
> > avaliable slots for network cards).
> > 
> > I was wondering if it is possible to create a separate class for every
> > range matching on giaddr field. However I'm neither sure if it is
> > possible nor if that can guarantee that a DISCOVER came from a device
> > behind the router that giaddr is stating it came from.
> 
> Matching on giaddr is an intrinsic functionality of DHCP servers.  
> Just define non-shared networks with multiple subnet statements, and 
> it will work automatically as long as the giaddr matches the subnet.
> 
> An issue arises if you wish to use different IP ranges for different 
> routers/giaddrs in the SAME subnets.  Then you must use 
> shared-networks and some other classification method for clients.  I 
> believe you can match on giaddr in a class for this, or use relay 
> agent information options.  A problem may arise when the unicast part 
> of a DHCP exchange doesn't use the relay agent, thus not being 
> classified correctly based on giaddr (0.0.0.0 in the unicast case) or 
> relay agent information options (non-existent in the unicast case).
>