New install - Handset doesn't connect

Hi Guys,
I’ve just completed a new build of FreePBX, Asterisk and CentOS 6.7, the server is remote to the building.

My status shows:

`SYSTEM INFORMATION
Asterisk   = ONLINE  | Dahdi     = ONLINE  | MySQL     = ONLINE
SSH        = ONLINE  | Apache    = ONLINE  | Iptables  = ONLINE
Fail2ban   = ONLINE  | Internet  = ONLINE  | Ip6Tables = ONLINE
Disk Free  = ADEQUATE| Mem Free  = ADEQUATE| NTPD      = ONLINE
SendMail   = ONLINE  | Samba     = OFFLINE | Webmin    = ONLINE
Ethernet0  = ONLINE  | Ethernet1 = N/A     | Wlan0     = N/A
---------------------------------------
PIAF Installed Version   = 3.0.6.7 under *KVM*
FreePBX Version          = 12.0.76.2
Running Asterisk Version = 12.8.1
Asterisk Source Version  = 12.8.1
Dahdi Source Version     = 2.10.0.1
Libpri Source Version    = 1.4.15
IP Address               = **.***.**.*** on eth0
Operating System         = CentOS release 6.7 (Final) ><
Kernel Version           = 2.6.32-573.8.1.el6.x86_64 - 64 Bit`

My handset is Cisco 7940G running sip firmware. The handset is accessing the server over the internet as it is downloading the configuration files etc from the tftp server however it is refusing to connect.

Within Asterisk I’ve got an extension set up called 101.

My phone cnf file is
# Line 1 Settings line1_name: "101" ; line1_displayname: "101" ; line1_shortname: "101" ; line1_authname: "101" ; line1_password: "*********" ; proxy1_address: "***.**.***.**" ; proxy1_port: "5061";

How can I work out why my handset is failing to connect to my remote pbx?