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ryan rey rupa

CUCM Register device from external network.

Hi Guys,

     Im still new to this cisco PABX setup. I used to handle data but now I have to explore the voice too. I have a cisco cucm 8.6.2 running, My question is what are the ways to register a device (preferablly SIP) to cucm from external network. Meaning the device is located outside the office network. One thing that comes in my mind is trough VPN, aside from that? for VPN are there any other required special setup or configurations?

Any comments or suggestion is highly appreciated.

Thank you!



Nizar Abuseni
Cisco Employee

Yes through VPN you can do that. You have to make sure that the Phone and callmanager can reach each other.

Hi Nizar,

     Thank you for your reply. I was thinking aside from VPN what can I do? Like directly configuring my CUCM IP from my SIP device. Then just use port forwarding pointing my public IP to my CUCM local ip. Is it possible? anyone tried that?

Yes you can like that, but it is not recommended because your callmanager will be accessed publicly. But you will face problem with RTP traffic, because the phone will reach the CUCM but not other devices.

Better solution is by:

1- Configuring VPN on ASA or Router in both sides.


2- Use VPN feature in CUCM, but I am not sure if it supports SIP Phones,please check the bellow link:


Best regards,

Yes I will get into that VPN solution. most probbably tha's what I would choose. Going back I'm just curios what will be the process on registering to cucm using public IP?

Well registering the phone is not enough to make and receive calls. When the phone is registered with CUCM, this means that the phone can reach the cucm for signaling purpose. in other word if the phone can reach only the cucm then when making calls you will not hear anything. The phone should reach endpoint by ip connectivity also in order to make calls, also voice gateways should be reachable for PSTN calls.

Yep, I think firewall management can handle that issue. Have you tried doing it? using port forwarding?

I did once by NATing ip addresses on both sides.

Nating both sides means you need the static public IP of the external network. Not ideal when you want to install the Softphone to a Mobile Device.

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