VOIP Tech Chat → [General] Phones stop registering

Hi

I have a client that installs VoIP phones on
customer premises and connects these to his
Centrex provider.

The sites usually have both an SDSL and an ADSL
link.

He configures the local Mikrotik router to
direct all VoIP traffic via the SDSL line.

Apparently on one of his previous installations
the phones cease registering to the Centrex and
remain disconnected.

If he disables the SDSL link the phones connect
and remain connected via the ADSL link.

At first glance he thought it was an issue with
the SDSL link but soon realized that the issue
was related to the presence of the two uplinks.

My client believes that the phone's DNS lookups
could be to blame for this situation.

I on the other hand think that maybe it's because
at some point the trafic sent is responded to via
the same uplink.

The weird thing is that if there was an issue then
surely the phones wouldn't refuse to register, full
stop.

In the present case they register and stay registered
according to the registration frequency setting, until
the point at which they just stop registering; which
could be a few hours later.

Any other ideas or suggestions ?

regards
yann

I believe that you have received no replies because insufficient information is present.

Phone make / model ?
Server software?
Protocol being used, e.g. SIP over TLS ?
ISP?
Does the Mikrotik get a public IP address on both of its WAN interfaces? If not, please explain, e.g. there is a Livebox/Neufbox/Freebox/Bbox in the path.

If you want to take a potshot at the problem, try configuring the phones to use 8.8.8.8 and 8.8.4.4 (Google) for DNS, ignoring what may be supplied by DHCP.

Some ISP (and other) DNS servers will return the address of an ad server on a failed lookup (rather than the correct NXDOMAIN response). The ad server will of course not respond to SIP requests and if for some reason the phone doesn't repeat the failed lookup, it will be stuck failing to register.

If you can't find the trouble quickly, try to see what is actually going wrong. Mikrotik has a wonderful packet capture feature that can stream to a remote machine (at the customer's or at your client's) running Wireshark. It uses TZSP, so Wireshark can parse SIP, DNS, etc., as if the traffic were on its own LAN. »wiki.mikrotik.com/wiki/M ··· _Sniffer »wiki.mikrotik.com/wiki/E ··· ireshark .

Assuming that when the phones stop registering, disabling the SDSL allows them to register again, without restarting the phones or server, that probably indicates that register requests are being sent out but replies are not reaching the phone. I'd first capture on the LAN side to confirm that the requests are destined for the correct IP address and port. If so, check whether replies are missing or reflect error status. If correct requests are going out but nothing is coming back, then take a look at the interface to which the SDSL is connected.

I have a few ideas.. But before making suggestions on what to try..

You are being contracted by the VoIP company to fix this issue?Does this particular site have both?Why does your client believe this?

If that is the case, hardcode the IP into the phones.

What is the Mikrotik config? Which firmware version?Do you or your client have a syslog server? What do the logs indicate? (Both phone and server side)Huh?What do they do to get the phones to re-register?
Can the not-registered phones still make outgoing calls?

What model(s) of phones? Which firmware?

Are all the sites the same?

What is different about this site compared to the others?

Lastly, if the SDSL is just for the VoIP, why not have a separate router for the VoIP, so not needing to do dual-WAN configuration.

Thanks for your reply Stewart

2x Cisco SPA525G2 phones
Centrex : Centile Telecom Application S.A.S.
ISP: OpenIP
Protocol: SIP
Both WAN interfaces have a fixed IP addresses

Thanks for your response Kevin

My client is the one who contacted me about this issue
This particular site does indeed have both uplinks
My client believes the issue lies with DNS because he can't see what else it could be
The Mikrotik RB2011UAS-2HnD is using the latest ROS
I don't have access to the phones so don't have any logs to sift through
Huh: I got it mixed up, sorry; I meant that the response doesn't come back through the same uplink it went out
If you disconnect/disable the SDSL link the phones register immediately
No, once the phones are unregistered they are no longer able to operate
I have a feeling this is his first Mikrotik installation
The client wants to have load balancing and failover functionality for all traffic