[Dnsmasq-discuss] dhcp doesn't work

[Simon Kelley]

Johannes Graumann wrote:
> Hello,
> 
> I'm trying to take load of a somewhat overloaded little server by handing
> dhcp to the already dns-caching dnsmasq. I can't get it to work. The client
> doesn't get it's ip. The dhcpd.conf I'm trying to mimic looks like so:
> 
> ddns-update-style none;
> option domain-name-servers 192.168.0.1;
> option time-servers     192.168.0.1;
> default-lease-time 86400;
> max-lease-time 604800;
> authoritative;
> log-facility local7;
> subnet 192.168.0.0 netmask 255.255.255.0 {
>         deny unknown-clients;
>         option routers 192.168.0.1;
> }
> host angband {
>         hardware        ethernet        00:E0:81:70:0C:BE;
>         fixed-address   192.168.0.2;
> }
> 
> The dnsmasq.conf I am trying is this:
> 
> no-resolv
> server=213.191.74.18
> server=213.191.92.86
> interface=eth1
> dhcp-range=192.168.0.3,192.168.0.10,12h
> dhcp-host=00:E0:81:70:0C:BE,192.168.0.2,angband
> dhcp-option=42,0.0.0.0
> 
> Can anybody here pinpoint what I'm screwing up?

The classic answer is probably firewall rules: ISC dhcpd bypasses the 
firewall: dnsmasq doesn't. The requirements are in the FAQ. Quote:

    For the dnsmasq daemon to operate it's vital that UDP packets to
    and from ports 67 and 68 and broadcast packets with source
    address 0.0.0.0 and destination address 255.255.255.255 are not
    dropped by iptables/ipchains.

Oh, and you can replicate "deny unknown-clients;" by changing the 
dhcp-range line to

dhcp-range=192.168.0.3,static,12h

"log-facility local7;" becomes

log-facility=local7

and "authoritative;" becomes

dhcp-authoritative

Which raises another potential problem: if a client already has a lease 
with the old server, and just tries to renew it, then dnsmasq will 
ignore it unless dhcp-authoritative is set. Releasing the DHCP lease and 
re-aquiring a new one should still work; if that's broken, look to your 
firewall.

Cheers,

Simon.


> 
> Thanks, Joh
> 
> 
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