[Dnsmasq-discuss] DHCP request not getting to dnsmasq

[Guennadi Liakhovetski]

Please, do not drop the list from cc. I am slowly unning out of ideas, and 
you might need help from others on the list.

On Tue, 25 Dec 2007, Robin Atwood wrote:

> On Tuesday 25 Dec 2007, you wrote:
> > On Tue, 25 Dec 2007, Robin Atwood wrote:
> > > On Tuesday 25 Dec 2007, you wrote:
> > > > > Yes, I see:
> > > > >  # tcpdump -i eth0 port 67
> > > > > tcpdump: verbose output suppressed, use -v or -vv for full protocol
> > > > > decode listening on eth0, link-type EN10MB (Ethernet), capture size
> > > > > 68 bytes 23:00:37.564313 IP 0.0.0.0.bootpc > 255.255.255.255.bootps:
> > > > > BOOTP/DHCP, Request [|bootp]
> >
> > So, DHCP packet arrives on your dhcp / dnsmasq server on eth0.

Ok, the above is of course not very verbose. Could you do

tcpdump -w /tmp/dnsmasq.pcap -i eth0 -s 512 port 67

to capture the latpot request and then send the resulting file? You may 
also filter on your laptop ethernet address like

tcpdump -w /tmp/dnsmasq.pcap -i eth0 -s 512 port 67 and ether src <laptop-mac>

to make sure no sensitive information gets captured, and just examine the 
contents with ethereal afterwards. If you're still concerned, you may send 
the file to me only.

Below your original reply for the list again.

> > > > > but absolutely nothing in the dnsmasq logging. Below are all the
> > > > > non-comment lines in my dnsmasq.conf. This must be something very
> > > > > basic!
> > > > >
> > > > > domain-needed
> > > > > resolv-file=/etc/resolv-upstr.conf
> > > > > strict-order
> > > > > local=/binro.org/
> > > > > interface=eth0
> > > > > domain=binro.org
> > > > > dhcp-range=192.168.1.32,192.168.1.63,12h
> > > > > dhcp-option=option:router,192.168.1.1
> > > > > dhcp-option=42,0.0.0.0
> > > > > log-dhcp
> >
> > This tells, that your eth0 network is 192.168.1.0.
> >
> > > > strace -o /tmp/dnsmasq.trace -s 256 -tt -p `pidof dnsmasq`
> > >
> > > I took the strace (attached) but cannot see anything to do with DHCP. I
> > > also checked the Gentoo build options and there is nothing disabling
> > > DHCP. It's a mystery.
> >
> > But in your strace we see this:
> >
> > sin_addr=inet_addr("203.146.0.20")
> 
> That is the address of the up-stream DNS server at my ISP.
> 
> > Hm, could you try this on your server as root:
> >
> > netstat -lp | grep bootps
> 
> This shows:
> 
> udp        0      0 *:bootps   *:*                             2595/dnsmas
> 
> > do you have any iptables rules active?
> 
> Oh yes! But anything is accepted on the 192.168.0.0/255.255.0.0 sub-net. We 
> can see the bootp packet is getting through to my server.

Don't know if any iptables rule can get between tcpdump and an 
application...

Thanks
Guennadi
---
Guennadi Liakhovetski