[Dnsmasq-discuss] dnsmasq forwarding queries over VPN/IPSec

Ken Bantoft ken at netfunctional.ca
Mon Sep 28 16:25:41 BST 2009

On 28-Sep-09, at 11:12 AM, Simon Kelley wrote:

> Ken Bantoft wrote:
>> On 28-Sep-09, at 11:03 AM, Simon Kelley wrote:
>>> Ken Bantoft wrote:
>>>> Hi,
>>>> I've run into a case where I'd like dnsmasq to forward queries  
>>>> over an  IPSec VPN tunnel to nameservers on the far side, but  
>>>> this doesn't seem  to work as expected.
>>>> I've got 2 Interfaces - br-lan ( and ppp0 (PPPoE -   
>>>> 216.x.x.x).  IPsec is terminated on the same machine, so it has  
>>>> a  tunnel from to
>>>> dnsmasq is set to forward all queries to 10.x.x.10 and 10.x.y.10   
>>>> nameservers, which are across the tunnel in the datacenter.  What  
>>>> I'm  seeing with tcpdump is the requests going out the ppp0  
>>>> interface, with  the 216.x.x.x IP address.  I've tried a variety  
>>>> of options (bind- interfaces, listen-address), as I really want  
>>>> dnsmasq to bind only to  the br-lan interface, and use that  
>>>> address as the Source IP for the  forwarded queries, but no  
>>>> combination I've tried does the trick.
>>>> Any suggestions?
>>> Stop dnsmasq from looking for servers in /etc/resolv.conf with
>>> no-resolv
>>> in /etc/dnsmasq.conf and then specify them using "server=" lines  
>>> in /etc/dnsmasq.conf like this
>>> server=10.x.x.10 at br-lan
>>> server=10.x.y.10 at br-lan
>>> We've been here before....
>> That was my 1st step... so I do see it sending the requests to  
>> 10.x.x.10 and 10.x.y.10 as expected - just out the wrong interface...
>> Ken
> If this a routing problem? Dnsmasq can control the source address of  
> the packets, and the destination address is straightforward, but it  
> can't control how the kernel routes the packets: do you have a  
> route  to via the tunnel?

No route - it's Linux Kernel netkey IPsec stack, so no nice ipsec0  
interface - it's all done with the ip xfrm policies... which might be  
causing some grief, but it's difficult to tell.  Any debugging options  
for dnsmasq to have it printout the packets before it puts them on a  


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