[Dnsmasq-discuss] UDP DNS Requests

[Mike Owens]

I am able to get a UDP reply from the socket using nc. TCP requests are
handled fine. No UDP requests show up in the log. UDP request to the
upstream DNS server are answered fine when queried directly. Is there
anything that can cause UDP requests to be blocked other than a firewall?
The router isn't blocking UDP. This seems to be only dnsmasq.

Output from Dig:

[ ~]$ dig debian.org @192.168.1.115

; <<>> DiG 9.7.3-P3-RedHat-9.7.3-8.P3.el6 <<>> debian.org @192.168.1.115
;; global options: +cmd
;; connection timed out; no servers could be reached
[ ~]$ dig +tcp debian.org @192.168.1.115

; <<>> DiG 9.7.3-P3-RedHat-9.7.3-8.P3.el6 <<>> +tcp debian.org @
192.168.1.115
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 34510
;; flags: qr rd ra; QUERY: 1, ANSWER: 2, AUTHORITY: 0, ADDITIONAL: 0

;; QUESTION SECTION:
;debian.org.            IN    A

;; ANSWER SECTION:
debian.org.        1992    IN    A    206.12.19.7
debian.org.        1992    IN    A    128.31.0.51

;; Query time: 56 msec
;; SERVER: 192.168.1.115#53(192.168.1.115)
;; WHEN: Wed Jan 11 17:47:47 2012
;; MSG SIZE  rcvd: 60


Corresponding log entries:

Jan 11 18:16:36 dnsmasq[6821]: started, version 2.57 cachesize 150
Jan 11 18:16:36 dnsmasq[6821]: compile time options: IPv6 GNU-getopt DBus
I18N DHCP TFTP IDN
Jan 11 18:16:36 dnsmasq[6821]: warning: ignoring resolv-file flag because
no-resolv is set
Jan 11 18:16:36 dnsmasq-dhcp[6821]: DHCP, IP range 192.168.1.2 --
192.168.1.99, lease time 12h
Jan 11 18:16:36 dnsmasq[6821]: using nameserver 192.168.1.100#53
Jan 11 18:16:36 dnsmasq[6821]: read /etc/hosts - 7 addresses
Jan 11 18:17:07 dnsmasq[6840]: query[A] debian.org from 192.168.1.102
Jan 11 18:17:07 dnsmasq[6840]: forwarded debian.org to 192.168.1.100
Jan 11 18:17:07 dnsmasq[6840]: reply debian.org is 206.12.19.7
Jan 11 18:17:07 dnsmasq[6840]: reply debian.org is 128.31.0.51

Nothing from the UDP request.



On Wed, Jan 11, 2012 at 2:24 PM, <
dnsmasq-discuss-request at lists.thekelleys.org.uk> wrote:

> Message: 4
> Date: Wed, 11 Jan 2012 18:02:35 +0000
> From: Simon Kelley <simon at thekelleys.org.uk>
> To: dnsmasq-discuss at lists.thekelleys.org.uk
> Subject: Re: [Dnsmasq-discuss] UDP DNS Requests
> Message-ID: <4F0DCEBB.7010407 at thekelleys.org.uk>
> Content-Type: text/plain; charset=UTF-8; format=flowed
>
> On 11/01/12 17:47, Mike Owens wrote:
> > I was hoping for some more ideas on why DNS won't respond to UDP
> > requests but responds just fine to TCP requests. I've trimmed down the
> > dnsmasq.conf file to the minimum for what I need. The conf is in my last
> > message. I've commented out all unnecessary enties in the host file.
> > I've disabled access to the resolv.conf file. I am explicitly
> > referencing one and only one DNS server for forwarding. The referenced
> > DNS server responds to UDP requests just fine. I've disabled and removed
> > the firewall on the dnsmasq machine. What are the other possible causes
> > of not receiving responses from UDP requests?
> >
>
> Broadly, there's several places that the query could get lost, either
> it's not getting to dnsmasq, or dnsmasq isn't forwarding it, or dnsmasq
> is forwading it and it's not getting upstream or it's getting upstream
> and the reply is getting lost.
>
> Setting
>
> log-queries
>
> and examining the log should tell you which of these is true, but I
> don't think we've seen any logs posted for UDP queries.
>
>
> Can you dig <domain> @127.0.0.1 on the machine running dnsmasq?
>
> Cheers,
>
> Simon.
>
>
>
>
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