[Dnsmasq-discuss] Failing to get DHCP responses on OpenBSD

[Fabian]

On Sat, 7 Dec 2019 21:44:08 +0100
Geert Stappers <stappers at stappers.nl> wrote:

> A. stop dnsmasq and check again what fstat says about port 67

Nothing else is listening on that port.

> B. try only 1 interface  (add the others I/F when 1 works)

Could not make that work. :-(

> >         inet 182.227.21.34 netmask 0xffffe000 broadcast 182.227.21.255  
> 
> FWIW:
>   netmask and broadcast don't match. Make the broadcast 182.227.31.255
>   to match the netmask

Sorry, my mistake, I had replaced the real IP address by some made up
numbers.

I was playing around a bit more with fstat and netstat and noticed one
difference between dhcpd and dnsmasq - dhcpd binds to bpf (Berkeley
Packet Filter) and not a datagram socket like dnsmasq does. I
definitely see a UDP datagram coming in for port 67 with tcpdump when
dhcpd is running and it is replying instantly with a UDP datagram. So
something makes the bpf socket see the traffic while the datagram
socket does not?

OTOH, why would I be the only OpenBSD user that has that issue? Maybe
there is some fancy OpenBSD security mechanism that I am not aware of?
When I run dnsmasq for testing, I am running as root. Running it with
the regular rc scripts, it runs with user _dnsmasq. I am getting the
same behavior from dnsmasq in both cases however.

-- 
Fabian