On 14/04/2020 18:51, Josh H wrote:
> Hi there,
> 
> I'm receiving no DHCPOffer back from my DHCPDiscover. However, I can
> tcpdump the machine running dnsmasq and it is receiving the DHCPOffer
> packets. 
> 
> Here's my very very simple dnsmasq.conf
> # To disable dnsmasq's DNS server functionality.
> port=0
> 
> # To enable dnsmasq's DHCP server functionality.
> dhcp-range=192.168.1.3,192.168.1.8,255.255.255.240,12h
> 
> # Set gateway as Router. Following two lines are identical.
> #dhcp-option=option:router,192.168.0.1
> dhcp-option=3,192.168.0.1
> 
> # Set DNS server as Router.
> dhcp-option=6,192.168.0.1
> 
> # Logging.
> log-facility=/var/log/dnsmasq.log   # logfile path.
> log-async
> log-queries # log queries.
> log-dhcp    # log dhcp related messages.
> 
> Here's the contents of /var/log/dnsmasq.log after running dhclient on a
> machine connected to the subnet:
> Apr 14 18:36:57 dnsmasq[1702]: started, version 2.80 DNS disabled
> Apr 14 18:36:57 dnsmasq[1702]: compile time options: IPv6 GNU-getopt
> DBus i18n IDN DHCP DHCPv6 no-Lua TFTP conntrack ipset auth DNSSEC
> loop-detect inotify dumpfile
> Apr 14 18:36:57 dnsmasq-dhcp[1702]: DHCP, IP range 192.168.1.3 --
> 192.168.1.8, lease time 12h
> 

So, nothing logged indicating that the DHCPDiscover has been recieved?
If not, my guess would be an iptables rules blocking incoming packets
sent to 255.255.255.255.

> I can see the service running with netstat -anp4:
> Active Internet connections (servers and established)
> Proto Recv-Q Send-Q Local Address           Foreign Address        
> State       PID/Program name    
> udp        0      0 0.0.0.0:67 <http://0.0.0.0:67/>            
>  0.0.0.0:*                           1702/dnsmasq        
> udp        0      0 0.0.0.0:1701 <http://0.0.0.0:1701/>          
>  0.0.0.0:*                           1607/xl2tpd         
> 
> There are no firewalls setup anywhere on my network for the moment. I
> have been able to get isc-dhcp-server to successfully allocate DHCP
> requests just fine however, so I don't think it's anything broken with
> DHCP in general. I'm running Linux kernel 5.6.2 and using dnsmasq from
> Debian Bullseye.

Working on ISC but not dnsmasq reinforces my diagnosis: dhcpd bypasses
iptables for such packets, dnsmasq doesn't.



Cheers,

Simon.


> 
> Hopefully someone can work out my issue!
> Thank you very much!
> 
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> 

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