Listening on interface without IP address

[Miloslav Hůla]

>> What could work would be something like this :
>>
>> shared-network VLAN-376 {
>>    subnet a.b.c.d ... {
>>      range a.b.c.e ; };
>>    subnet 10.1.120.0 ... {};
>> }
>>
>> And give the DHCP server an IP address in the 10.1.120.0/24 subnet.
>> The server will operate using the 10.1.120.0 subnet, and the 
>> shared-network statement will make it associate the a.c.b.d subnet 
>> with the same interface. You will need to setup routing so that 
>> unicast packets from the client at a.b.c.e can reach the server at 
>> 10.1.120.nn. This could be either by adding a 10.1.120.xx address to 
>> the router on VLAN 376, or by adding a route via some other route - 
>> for example routing to 10.0.0.0/15 to some other interface on the DHCP 
>> server. For the latter, the DHCP server will need to be listening on 
>> that interface.
> 
> Thank you! That's a great idea. Actually we already have VLANs with more 
> subnets, so it should work.

I deployed it for a first VLAN and it works, even without private range 
routing. Only I have to set:

server-identifier ...server-public-ip...;

for subnet with public IP range in shared-network VLAN-376.

First DISCOVER, OFFER, REQUEST, ACK are done by broadcast via eth0.376 
(interface with private IP), following REQUST, ACK are done by routed 
unicast (via. server public IP) and so as release.

Many thanks again.

Milo