[Dnsmasq-discuss] Assigning leases based on relay agent IP address?

[Brian Rak]

How can I use dhcp-match with the 'Relay agent IP address' part of the 
packet?


I'm trying to manage DHCP for a bunch of different networks with one 
DHCP server.  I'd like to determine which network to use based on which 
subnet the relay server's IP address is in.

I've got a bunch of lines like this:

dhcp-range=set:SUBNETID124862,10.237.2.65,10.237.2.126,auto,255.255.255.192,2h
dhcp-range=set:SUBNETID124844,10.237.4.1,10.237.4.62,auto,255.255.255.192,2h

However, when a DHCPDISCOVER comes in, dnsmasq just picks a random 
network to use.   As an example:

dnsmasq-dhcp[31908]: 2740340080 vendor class: udhcp 1.12.0
dnsmasq-dhcp[31908]: 2740340080 DHCPDISCOVER(eth1) 00:25:90:d7:c6:7c
dnsmasq-dhcp[31908]: 2740340080 tags: SUBNETID124844, eth1
dnsmasq-dhcp[31908]: 2740340080 DHCPOFFER(eth1) 10.237.4.39 
00:25:90:d7:c6:7c

The initial DHCPDISCOVER came in via 10.237.2.65, but a completely 
different subnet was used instead. (Also, is it possible to log the 
relay IP address?)

tshark shows this:

Bootstrap Protocol
     Message type: Boot Request (1)
...
     Bootp flags: 0x0000 (Unicast)
         0... .... .... .... = Broadcast flag: Unicast
         .000 0000 0000 0000 = Reserved flags: 0x0000
     Client IP address: 0.0.0.0 (0.0.0.0)
     Your (client) IP address: 0.0.0.0 (0.0.0.0)
     Next server IP address: 0.0.0.0 (0.0.0.0)
     Relay agent IP address: 10.237.2.65 (10.237.2.65)
     Client MAC address: 00:25:90:d7:c6:7c (00:25:90:d7:c6:7c)


This is with dnsmasq 2.71