[Dnsmasq-discuss] DHCP Relay Problem

[Michael Garrison Stuber]

Greetings!
     I'm trying to diagnose a problem with DHCP relaying via DNSMasq.  
I'm hoping someone can help, or at least point to what to investigate 
next.  I have a router running DNSMasq as a DHCP server.  I have a 
second router connected to the first, running DNSMasq as a relay.

[Main Router] 192.168.1.1 <--WAN-Link--> 192.168.1.2 [Remote Router] 192.168.10.1 <--Client-LAN--> DHCP client.

     When a DHCP client comes on to the Client LAN, it sends a DHCP 
request.  I see this in the Remote Router Log:

Feb 12 12:32:22 yew daemon.info dnsmasq-dhcp[7855]: DHCP relay 192.168.10.1 -> 192.168.1.1

     Remote Router forwards it the Main Router:

[Packets seen at Remote Router]

12:32:22.057611 Out 00:24:9b:29:81:f3 ethertype IPv4 (0x0800), length 
344: (tos 0x0, ttl 128, id 22793, offset 0, flags [none], proto UDP 
(17), length 328) 0.0.0.0.68 > 255.255.255.255.67: BOOTP/DHCP, Request 
[|bootp]
12:32:22.058858 Out bc:ae:c5:c3:00:4d ethertype IPv4 (0x0800), length 
344: (tos 0x0, ttl 64, id 38438, offset 0, flags [none], proto UDP (17), 
length 328) 192.168.10.1.67 > 192.168.1.1.67: BOOTP/DHCP, Request [|bootp]
[Packets seen at Main Router]
12:32:22.213469  In 68:72:51:88:69:b4 ethertype IPv4 (0x0800), length 
344: (tos 0x0, ttl 64, id 38438, offset 0, flags [none], proto UDP (17), 
length 328)
     192.168.10.1.67 > 192.168.1.1.67: BOOTP/DHCP, Request from 
00:24:9b:29:81:f3, length 300, hops 1, xid 0xf43325a2, secs 3072, Flags 
[Broadcast]
           Gateway-IP 192.168.10.1
           Client-Ethernet-Address 00:24:9b:29:81:f3
           Vendor-rfc1048 Extensions
             Magic Cookie 0x63825363
             DHCP-Message Option 53, length 1: Discover
             Client-ID Option 61, length 7: ether 00:24:9b:29:81:f3
             Hostname Option 12, length 10: "MTGS-SBOOK"
             Vendor-Class Option 60, length 8: "MSFT 5.0"
             Parameter-Request Option 55, length 13:
               Subnet-Mask, Default-Gateway, Domain-Name-Server, Domain-Name
               Router-Discovery, Static-Route, Vendor-Option, 
Netbios-Name-Server
               Netbios-Node, Netbios-Scope, Classless-Static-Route, 
Classless-Static-Route-Microsoft
               Option 252

     The main router responds:

[Packets seen at Main Router]
12:32:22.215239 Out 80:2a:a8:4f:c4:02 ethertype IPv4 (0x0800), length 
346: (tos 0xc0, ttl 64, id 33748, offset 0, flags [none], proto UDP 
(17), length 330)
     192.168.1.1.67 > 192.168.10.1.67: BOOTP/DHCP, Reply, length 302, 
hops 1, xid 0xf43325a2, secs 3072, Flags [Broadcast]
           Your-IP 192.168.10.133
           Server-IP 192.168.1.1
           Gateway-IP 192.168.10.1
           Client-Ethernet-Address 00:24:9b:29:81:f3
           Vendor-rfc1048 Extensions
             Magic Cookie 0x63825363
             DHCP-Message Option 53, length 1: Offer
             Server-ID Option 54, length 4: 192.168.1.1
             Lease-Time Option 51, length 4: 86400
             RN Option 58, length 4: 43200
             RB Option 59, length 4: 75600
             Subnet-Mask Option 1, length 4: 255.255.255.0
             BR Option 28, length 4: 192.168.10.255
             Domain-Name Option 15, length 8: "localnet"
             Domain-Name-Server Option 6, length 4: 192.168.1.1
             Default-Gateway Option 3, length 4: 192.168.10.1

[Packet seen at Remote Router]
12:32:22.062199   P 80:2a:a8:4f:c4:02 ethertype IPv4 (0x0800), length 
346: (tos 0xc0, ttl 64, id 33748, offset 0, flags [none], proto UDP 
(17), length 330) 192.168.1.1.67 > 255.255.255.255.68: BOOTP/DHCP, 
Reply, length 302, hops 1, xid 0xf43325a2, secs 3072, Flags [Broadcast]
           Your-IP 192.168.10.133
           Server-IP 192.168.1.1 [|bootp]

Unfortunately, the DNSMasq Process at the Remote Router never picks up 
the response to send it to the client. I've tried using the <interface> 
option of the --dhcp-relay option in DNSMasq, but it doesn't seem to 
make a difference. ipforwarding is on, and iptables is set to accept 
everything in both directions.  I can't tell whether DNSMasq at the 
Remote Router is receiving the response and ignoring it, or if it never 
makes it to the DNSMasq process.

Is there anyway to crank up the logging on DNSMasq even higher?  Am I 
right in thinking that DNSMasq should in fact receive this message, 
process it, and forward the response to the client?  Any tips on how to 
trouble shoot this?

-- Michael Garrison Stuber