DNS resolution problem


Good evening,

I am currently running in to an issue configuring my WP820. If set an IP address ( as sip server, everything works fine and the phone switches to “Registered” in Account status. If I change the sip server to a dns name (fritz.box), the phone is permanently “Unregistered”.

The logs of my DNS server show the request and the responses:
Mar 25 17:43:47 picard dnsmasq[4661]: query[A] fritz.box from
Mar 25 17:43:47 picard dnsmasq[4661]: /etc/hosts fritz.box is
Mar 25 17:43:47 picard dnsmasq[4661]: query[AAAA] fritz.box from
Mar 25 17:43:47 picard dnsmasq[4661]: config fritz.box is NODATA-IPv6 is the correct IP address. Surprisingly the phone also asks for an IPv6-resolution even though the phone is set to “IPv4 Only”.

debug syslog:
(unfortuately, I cannot put the log directly in this post, because I’m apparently not allowed to post more than two ‘links’).

Any help would be appreciated.



Hi, Is the sip port default "5060’?


Yes, it’s 5060. But, frankly speaking, I fail to understand how the port is related to my problem. The only change I made was swapping the ip address to a dns name. Everything else including the port remained unchanged.



the FritzBox has SIP built in, so nothing properly “external” will ever work for you.
I personally tested it for 2 days and then abandoned it. It’s not a Professional also lacks a serious firewall with ACLs, you can try it but I think you’re wasting your time.


What is your IPPBX ? is it back of the NAT?
IF it is asterisk base .
check the DNS server on IPPBX
and check the externip in sip.conf


Well, the FritzBox is only accessible from the inside, so no need for ACLs or a firewall. Did you abandon it because it didn’t work with Grandstream phones or because it didn’t match your use case?

My goal atm is just getting the phone to work but if it fails at basic functionality like dns resolution, I’ll probably have to send it back. A dedicated pbx is on the projects list, but that will have to wait and probably also need a working dns…



the reasons why I don’t use Fritzbox are exclusively professional and I wrote them down for you, I am an installer.
IP phones all work the same way, there is no worse or better. The important thing is to work with an infrastructure suitable to do VoIP, I don’t understand what you want to do with WP820, if you try to make me a scenario I can tell you mine if you want.



Can you take a one click debug with the “capture trace” option checked? Also I would enable/disable the “Account active” option of the account while the capture is running so that hopefully we can see the DNS resolution.



Thank you. Just wanted to confirm this was actually off-topic.


you opened the post, you asked me questions and I answered, if you don’t want answers, just don’t ask questions.
good job


I’m sorry if you got me wrong. I would actually really appreciate any help on the dns problem.


Thanks for tracking my actual problem down. Where should I send the debug data?



you asked me about Fritzbox, and I told you,
otherwise I already told you what I think.


A small preview:

The correct address is returned but the phone doesn’t really care, asks for an AAAA record and for A again and again.

with display filter
the results are completely empty. No single packet.



I am curious, are you trying to ultimately use split DNS?


Not really. The PBX only exists internally.


Then why the need for an FQDN at all if the IP is known and will never change? Just curious. I don;t really know the Fritz box, but see a lot if posts about issues.

The port may make a difference from a register standpoint. It may be worth a shot to try and specify and see what happens. I guess the other question is whether or not the WP sees the response?


Unbelievable. Explicitly adding the port did it. I can’t believe why
works but
doesn’t in contrast to

To answer your questions and wrap everything up:
-Even local ip addresses can change and after the last server migration using several cnames made my life much easier. In addition, dns names are self-explanatory.
-The WP definitely saw the response since the capture file was created directly on the phone. Nice debugging functionality btw.

/Edit: Since the post is closed: Could you just verify that the bug is reported to the developers?



Glad it’s fixed. Closing post