(Note, the title of the question Is there a way to classify DHCP requests based on the interface they're coming from? is what I want answered, but it doesn't actually ask that question for a non-dhcp relay situation, and the answer doesn't help here since I can't rely on a relay to set options for me).
I have a hypervisor (KVM) with isc-dhcpd at dom0, and I need to be able to PXE boot client VMs. This works fine for any one interface, but I can't seem to make it work for multiple interfaces - I have the following class for PXE:
class "pxeclients" {
match if substring(option vendor-class-identifier, 0, 9) = "PXEClient";
filename "pxelinux.0";
next-server 10.71.0.1;
}
The problem is that I have to pick which tftp interface I want to use for next-server. I need clients to pick the tftp server on their own subnet or they can't boot (but otherwise they all look the same, unless I can find some kind of match discriminant). Is there a way to create a class which matches on both PXE and the subnet I'm about to lease, or the interface the packet came in on?
Why not specify a tftp server that's a hop away? As long as your clients are receiving the appropriate default gateway this might be the easiest way to go.
That said, if you must support multiple interfaces -
It's possible to run multiple instances of dhcpd. Each would have its own configuration that would include entries to specifically bind said instance to a particular interface. To ease administration each config file could be set to include an additional configuration file that might contain other common settings. This would probably be fine for a relatively small number of interfaces (i.e. <= 10-20) but if it needs to scale much larger then I'd look into a proper L3 infrastructure with helper addresses/relays.