If you have a SonicWall firewall, you may be encountering one of two scenarios:
- Consistently relayed connections (blue icon)
- Direct connection (green icon) at first, then switching to a relayed connection shortly thereafter
This can be remedied by enabling a SonicWall feature called Consistent NAT. Consistent NAT enhances standard NAT policy to provide greater compatibility with peer-to-peer applications that require a consistent IP address to connect to.
This setting is usually located under SonicWall VOIP settings
If this does not completely resolve the issue, you may also need to perform port forwarding. Please see the Hamachi ports article