[Dnsmasq-discuss] Dnsmasq not always seeing unicast packets

Brian Haley brian.haley at hp.com
Mon Sep 12 19:59:31 BST 2011


I searched the archives, but didn't find anything that exactly fit the problem
I'm seeing.

I'm running dnsmasq-2.57 on Linux (Ubuntu 11.04), and am starting two dnsmasq
processes to serve DHCP on two interfaces to VMs I'm running.  Initial packets
(broadcast MAC/broadcast IP) are handled fine, but when it comes time to renew
and the VMs unicast the packet directly to the server IP, only one of the two
dnsmasq processes is getting the packets - the second one started.

It's hitting a "feature" in Linux that I've seen before, where if one socket is
bound to, then a second, only the second will see incoming unicast
packets on that socket.  I was hoping that using '--interface=br0' would solve
this, but dnsmasq doesn't seem to be doing an SO_BINDTODEVICE in that case, it
always bind's to and determines the incoming interface when the packet

I've tried all the various flag combinations, and still can't get these unicast
requests to work - is there something I'm missing that might help here?  Before
making a patch I figured I'd ask.

Thanks for any help,


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