SonicWall firewall devices often have issues maintaining the correct source port between initial registration and subsequent SIP signaling messages. This causes SIP packets to be rejected by Clearfly's Session Border Controller, as they do not match the IP and UDP source port of the initial registration.

Enabling what Sonicwall calls "Consistent Network Address Translation (NAT)" may resolve this issue.

Note: This recommendation only applies to older SonicWall models and firmware releases. Please see the following section on Source Port Remapping for information on how to fix source port preservation issues with newer SonicWall devices.

Newer SonicWall devices support the ability to disable source port translation on a per-policy basis. Typically, if enabling this option, you would first disable the Consistent NAT setting.

Please see SonicWall's KB article 188307 for more information regarding this configuration option.

If experiencing one-way audio issues between remote sites in a private network, try disabling Adtran's IP fast forwarding engine (FFE) on both the LAN and WAN interfaces

This is only applicable to handset-to-handset calls which are internal to the PBX and not being routed over Clearfly voice trunks.