etworks with VOIP might require SIP ALG (Session Initiation Protocol (SIP) Application Layer Gateway (ALG)) disabling on a Draytek router to prevent disruption VOIP functionality.
1) Logon to the Draytek via its web interface, under Management ensure that Telnet is enabled.
2) Use Telnet via the Windows Command Prompt. (if Telnet Client is not installed you can follow this guide)
3) Issue the following commands:
sys sip_alg ?
Checks if SIP ALG is enabled or not, if it is:
sys sip_alg 0