[Dnsmasq-discuss] A problem with kpac_dhcp_helper, dhcprelay, and dnsmasq

[Jon Nelson]

I'm not really sure which component isn't working quite right, but
I've got a situation that is probably a bit uncommon, and it's giving
me a bit of grief.

One of the networks I manage looks like this:

W <-> S <-> F

where W is a bunch of workstations, S is a server, and F is a
firewall. One half of S is in each network, and W and F are in
*different* networks. S does a limited amount of firewall/proxy
service.

dnsmasq always ran on F, providing dns.
Until recently, I ran the ISC dhcpd on S, providing addresses to the
workstations.
That worked fine.
Then I converted the dhcp config to a dnsmasq compatible one and moved
that functionality to the firewall, and ran ISC dhcp relay on the
server. After some initial fumbling, I got things working again.
Except for one thing.

KDE has a helper program, kpac_dhcp_helper, which is setuid root and
basically uses dhcp to retrieve PAC (proxy auto-configuration)
information. Windows also uses this mechanism, but I won't drag that
horrible morass into things. The helper used to work, but now it
doesn't.

dnsmasq reports this:

dnsmasq[3667]: DHCP packet: transaction-id is 1655180374
dnsmasq[3667]: Available DHCP range: 192.168.2.0 -- 192.168.2.150
dnsmasq[3667]: DHCPINFORM(eth1) 127.0.0.1 <null>

tcpdump shows the workstation making the request, the dhcp helper
re-making the request on the client's behalf, and the dhcp helper
**not** relaying the response back to the client. It does this
correctly for other dhcp requests but not this one. One might be going
wrong? Does dnsmasq have forwarding capability?

-- 
Jon