Call from internal extension to external extension failed

I have freepbx running inside a network. We have both extensions within and outside the network. The direct extension dial from outside to inside (like 111 to 211) is fine, however, from inside to outside fails (like 211 to 111). I have port forwarding on 5060 UDP/TCP and port range forwarding 10000 to 10201 UDP only. Appreciate it if someone can give me an idea where I can start troubleshooting this.