VoIP issues with calls or registration. - Router amendments
Standard Firewall Ports to bypass
Outbound Ports UDP Ports 4144 and 4244 UDP Ports 10000 to 32767 HTPPS Port 443 Sys Log Port 514 HTTP Port 80 DNS Port 53 NTP Port 123 Local ports Outbound requests to standard services will be from a random port (as for a PC) The following ports will be used to receive SIP and RTP packets UDP Ports 5061 and 5062 UDP Ports 4241 to 4280 UDP Ports 10000 to 32767
How to configure Draytek 27xx and 28xx series routers for VoIP
This config guide applies to following routers:
  1. Draytek Vigor 2820
  2. Draytek Vigor 2830
Settings to change:
  1. Disable SIP ALG
  1. SIP ALG Issues such as one way audio, lack of incoming calls, registration issues and etc. can be due to SIP ALG
To disable SIP ALG you have to telnet into the router and enter the following commands.
1./ sys sip_alg 0        - Disables SIP ALG
2./ sys commit          - Applies changes
3./ sys reboot            - Reboots router
     3. Allow traffic to/from the following IP addresses: and and
     4. Update Firmware to latest version
         Once the router is back online, reboot the IP phone or press re-register.
Incoming Call Problems
This is caused by a large IP SIP packet that is fragmented, but the router will not forward it. I understand that the new version will work if the checkbox under firewall -> general setup -> Accept large incoming fragmented UDP or ICMP packets is UNTICKED. This is the opposite to what you would expect.
     5. Untick "Accept large fragmented UDP packets" under the firewall configuration
     6. Disable Call Filter and Data Filter
     7.Into BANDWIDTH MANAGEMENT, then QUALITY of SERVICE - Tick enable the First Priority for VoIP SIP/RTP