[Dnsmasq-discuss] DHCP errors with vlans and multiple subnets

Simon Kelley simon at thekelleys.org.uk
Mon Mar 3 13:31:25 UTC 2014

First stage is to set log-dhcp in your configuration, which will add 
lots of extra useful information to the logging.


,On 03/03/14 13:20, David Joslin wrote:
> I have dnsmasq (version 2.69test8-78-g6e0290a) on a router running the
> tomato firmware (and I hope it's OK to post questions about such a
> router here). My network is split into several vlans, each with its own
> subnet, and one of the vlans has several wi-fi access points which
> obtain their IP addresses from the router using DHCP. The access points
> all have entries in the dhcp-hosts file reserving certain IP addresses
> for them. Up till recently everything was working fine - the access
> points always picked up the correct addresses.
> However, something weird is now happening. When the access points now
> request addresses, dnsmasq is offering addresses from the other subnets
> and isn't offering the addresses reserved in dhcp-hosts. Dnsmasq then
> logs an error saying that the offered address conflicts with the address
> recorded in the hosts file.
> The messages from the log are shown below.
> I've checked over and over again and I can't find anything that's
> changed in the configuration of the network or router and I can't work
> out what's causing this.
> Any help would be gratefully received.
> Thanks.
> David
> DHCPDISCOVER(br0) dc:9f:db:e8:98:b8
> DHCPOFFER(br0) dc:9f:db:e8:98:b8
> DHCPDISCOVER(br1) dc:9f:db:e8:98:b8
> DHCPOFFER(br1) dc:9f:db:e8:98:b8
> DHCPDISCOVER(br2) dc:9f:db:e8:98:b8
> DHCPOFFER(br2) dc:9f:db:e8:98:b8
> DHCPREQUEST(br0) dc:9f:db:e8:98:b8
> DHCPACK(br0) dc:9f:db:e8:98:b8 Room4UAP
> not giving name Room4UAP to the DHCP lease of because the
> name exists in /etc/dnsmasq/hosts/hosts with address
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