Sonicwall and SIP
The issue is that the default UDP connection timeout is setup to 30 seconds, which is shorter than the SIP registration expiration period.
The solution to the problem is to increase the UDP connection timeout to something larger than your SIP registration expiration period so that NAT connection will be kept open by the router.
- Method 1: You could do this for all UDP connections by just changing the value on the default rule in Firewall -> Access rules -> LAN>WAN. This is really an undesired method as it causes the router to track all UDP connections 10 times longer, when we really only need specific connections tracked longer.
- Method 2: Create a new LAN>WAN firewall access rule to match specific traffic. Under the Advanced options set the UDP connection timeout to 300 seconds (or something larger than the SIP registration expiration interval).
- Regardless of the above method, it is suggested to CHECK the Enabled consistent NAT box under VoIP -> Settings.