[Unbound-users] interface: apparently not working

Steve Jenkins stevejenkins at gmail.com
Wed Sep 21 22:36:29 UTC 2011

On Wed, Sep 21, 2011 at 3:35 PM, Anand Buddhdev <anandb at ripe.net> wrote:
> On 21/09/2011 18:28, Steve Jenkins wrote:
> Hi Steve,
>> 3) From the server on subnet C: unbound answers queries made ONLY to
>> its IP address on Subnet A, but does not respond to queries made to
>> its address on Subnet B.
> This may be happening because you've configured unbound to listen on
> What can happen is that the query is directed to address B, and
> unbound looks up the answer. It then wants to send the reply, and it
> sets the source address to This leaves the decision up to the
> kernel, which can set the source address of the response packet to
> address A. Your client is probably getting the response packet, but like
> any good client, it can't use this response, because it came from an
> address different to the one it sent its query to.
>> 4) From a remote server on still another subnet (we tested with a
>> shared host we had shell access to), identical results to case #3
>> above.
> This is the same as above.
>> I turned verbosity all the way up to 5 in the logs, and in cases #3
>> and #4 above, unbound does see the query. It just doesn't respond.
>> I was able to work around this by commenting out both the interface:
>> and ::0 lines and replace with:
>> interface:
>> interface: ::1
>> interface: IP on Subnet A
>> interface: IP on Subnet B
> This works fine, because now unbound is now listening on explicit
> interfaces. When it constructs a response packet, it will set the source
> address to whichever address it received the query on, so things will work.
>> So I'm glad I was able to work around it, but I'm curious why
>> interface: didn't work as it should. Any ideas?
> It's all got to do with routing in the kernel, and not unbound.
> Regards,
> Anand Buddhdev

Excellent explanation. Thank you. :)


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