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Can't get phones to register with CUCM through a VPN.

I'm trying to set up VoIP capabilities through a VPN to a remote site and cannot get the phones to register.

Possible relevant hardware info:
The CUCM at the main site is version 7.1
The main site firewalls are ASA5585-X's running IOS 8.4.4
The remote site firewall is an ASA5520 running IOS 8.4.7

The remote site switch, a 3750E, is the DHCP provider for both phones and computers

The DHCP configuration for the phones includes the option 150 ip line pointing to the IP address of the UCM.

This is how my other remote sites are set up, but they don't utilize a VPN for connectivity to the main site.

I can ping from the remote switch to the CUCM and I can ping from the CUCM to the remote phone vlan's IP address, which would infer that the issue is not a matter of non-connectivity.

When a phone is plugged in, the switch manager shows that the phone receives an IP address, but  the phone does not respond to ping attempts.

Scrolling through the network configuration on the phone, the TFTP server sand other pertinent IP addresses are correct, but the phone was set up at the main site, so I don't know if it's receiving that info or if it's simply retained from the earlier configuration.

What would be the next step in tracking down the cause?


Sreekanth Narayanan
Cisco Employee

The first step would be packet captures from the phone or the switch port where the phone is connected so we see what the phone is doing. Is the phone supposed to establish VPN connection to main site or is the VPN tunnel transparent to it?

Thanks for the reply.

The tunnel is transparent.

I'll see what Wireshark shows.

Hi,  where you able to see this issue? I have a similar. Issue with a Cisco 7811 on a remote site trying to connect  thru VPN to Cucm on.  both sides have a mikrotik hardware for. Vpn

Sadly, no.

This was a transitional setup and, once we relocated the group it serviced, we no longer needed the remote site.

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