[Dnsmasq-discuss] Re: Re: DCHP server not assign IP addresses

Troy Piggins troy at piggo.com
Tue Nov 18 06:09:30 GMT 2008

* Rune Kock wrote :
>* Troy Piggins wrote:
>> * Rune Kock wrote :
>>>* Troy Piggins wrote:
>>>> My dnsmasq 2.41 doesn't seem to be assigning DHCP IP addresses.
>>>> Been running the server for some time, but mainly for the DNS
>>>> side of things.  The IP addresses for most machines on my network
>>>> are static, so hasn't been a problem.  But I'm trying to connect
>>>> to a NAS (WD My Book World Edition) which I believe needs a DHCP
>>>> server to get an IP address, and I can't interface with it to set
>>>> it up without one.
>> [...]
>>> 2) Check your firewall settings.  The following is from dnsmasq's FAQ:
>>>    The first thing to check is the broadcast address set for the
>>>    ethernet interface. This is normally the adddress on the connected
>>>    network with all ones in the host part. For instance if the
>>>    address of the ethernet interface is and the netmask
>>>    is then the broadcast address should be
>>> Having a broadcast address which is not on the
>>>    network to which the interface is connected kills things stone
>>>    dead.
>> Not sure where this is set in dnsmasq.conf?  The only things I
>> have set are shown below[1].  Everything else, I assume, is the
>> default.  I searched the excellently commented dnsmasq.conf file
>> for "broadcast", and thought I'd try the "dhcp-authoritative"
>> command to see if that helped.  It didn't.
> Well, this part is about the setup of the network interface.  Check
> with ifconfig.

Aah, of course.  Sorry.

eth1      Link encap:Ethernet HWaddr 00:19:66:40:80:8d
          inet addr: Bcast: Mask:

>> The only other thing I could find was:
>> # Send options to hosts which ask for a DHCP lease.
>> # See RFC 2132 for details of available options.
>> # Note that all the common settings, such as netmask and
>> # broadcast address, DNS server and default route, are given
>> # sane defaults by dnsmasq. You very likely will not need any
>> # any dhcp-options. If you use Windows clients and Samba, there
>> # are some options which are recommended, they are detailed at
>> # the
>> # end of this section.
>> # For reference, the common options are:
>> # subnet mask - 1
>> # default router - 3
>> # DNS server - 6
>> # broadcast address - 28
>> But couldn't find what the 28 signified.  Shed any light?
>This is irrelevant.  It's about specifying broadcast to the client.
>>>    The second potential problem relates to firewall rules: since the ISC
>>>    daemon in some configurations bypasses the kernel firewall rules
>>>    entirely, the ability to run the ISC daemon does not indicate
>>>    that the current configuration is OK for the dnsmasq daemon.
>>>    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 and destination address are not
>>>    dropped by iptables/ipchains.
>> Both ports allow UDP:
>> $ sudo iptables-save | grep 67
>> -A udpincoming_packets -p udp -m udp --sport 67:68 --dport 67:68 -j ACCEPT
> I'm not entirely fluent in iptables syntax, but to me this sounds like
> "accept packets with source port 67/68 AND dest port 67/68".

I see.  You're interpretation is correct.  I thought the requests
only came and went on those ports.

> I believe that you need "accept source port 67/68 OR dest port
> 67/68".

I split the rules up as you suggested.

It still is not assigning addresses.

Troy Piggins | http://piggo.com/~troy
Peter Anspach's Top 100 Thing's I'd Do If I Ever Became An Evil Overlord:
94. When arresting prisoners, my guards will not allow them to stop and grab a
useless trinket of purely sentimental value.

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