Phones on VLAN drop calls after 30 seconds


I am testing VLAN implementation. Set one phone to VLAN 20, DHCP and address work correctly. When placing a call all works fine until the call drops after 30 seconds. All phones not on this VLAN work properly. Is the problem with NAT on the router or in the UC6202?


I have all phones and the UCM on vlan 101 using a Mikrotik router providing the VLan and IPs via VLan 101 requests, all working well, no drop outs at all for a few years now - production environment.

Can you describe in more detail what is providing the DHCP IP addresses and VLan tagging.


I am new to VLANs so forgive my lack of knowledge. Calyptix Firewall/Router is providing VLAN and DHCP, regarding the tagging, I don’t know how to answer that. I set the phone to VLAN 20 in the advanced network settings.


Is the UCM in switch mode?

My system set up is as follows:

  • Mikrotik 3000 series router - Vlan 101 with DHCP server enabled - plugged into Netgear Prosafe switch - QOS also enabled to allow VLan 101 to be prioritised
  • Netgear Prosafe POE switch with VLan tagging support - 101 honoured across all ports
  • UCM plugged into POE port of switch VLan 101 on Network interface static IP
  • Handsets plugged into POE port of switch with VLan 101 and DHCP on Network interface

Thats the setup for my system in the office, does that look similar to what your environment looks like?


Yes very similar, UC is in switch mode. Unifi switch with all ports accessible for VLAN 20 and default. Is your UC on the same VLAN as the phones?


Yes the UCM is on the same vlan - the router does the translation for anything not on the vlan


OK, do you know if the UC has to be on the same VLAN? Shouldn’t the router pass the traffic and not allow the calls to drop after 30 seconds?


In my set up the UCM is on the same VLan as the phones… I havent had an issue with dropping of calls in my scenario but yours sounds like there is a timer causing the issue.

If you do a call extension to extension on the same vlan does it work correctly or still drop 30 seconds after the call is established?


Ext. to Ext. the call does not drop. I am talking with a tech from Calyptix to see if there is any config in the Router that could be causing this.


Ask the router tech to help you with QOS for Voice calls (SIP and RTP - UDP 5060 and UDP 10000-2000)

Voice ISP external IP - Destination Nat to the IP of the IPPBX (UCM) for the above ports


You lost me

Voice ISP external IP - Destination Nat to the IP of the IPPBX (UCM) for the above ports

Where would I find this setting?


Where I am we use a Broadsoft sip trunk - telephone calls via our Broadworks service through our internet connection through the Mikrotik to the IPPBX ucm.
I made the assumption you were using a sip trunk from an external voice provider…


Yes we are using a SIP trunk, however to clarify the phones that are not on the VLAN still work properly. Only one on VLAN is having this issue. Any settings in the SIP provider would affect all the phones.


This still does sound like a timer… is NAT Enable Direct Media turned on under extension settings for the vlan extension?


Presumably the vlan is using a different LAN subnet than the others. Did you remeber to add that LAN subnet to the local network settings in the UCM…PBX settings, SIP settings, NAT?


NAT Enable Direct Media was set to “No” I have changed it to “Yes” and will try that

I did add the additional LAN subnet


@lpneblett I suspect the RTP stream is dieing after the 30 second period…

a Pcap will identify whats happening…


try vlan extension to non vlan extension call to see if it dies then


I don’t know what this means


When I called from ext. to ext. earlier that call did not die