Set Up Remote Phone
Cisco IP Phones that are configured for SSL VPN to ASA using the built-in client in a remote locaiont (for example, a home office) have a special configuration requirement.
We recommend that you provide the phone with an Alternate TFTP server setting manually. This setting allows the phone to download the configuration and other files from TFTP. The phone in a remote location (home office) cannot correctly provide OPTION 150 to the phone using DHCP.
The IP phone can register to the last-known Cisco Unified Communications Manager, but any configuration updates cannot applied until you configure the manual TFTP server address.
On the phone, select Applications.
Navigate to the IPv4 Settings window.
Scroll to the Alternate TFTP option and set the field to Yes.
In the TFTP Server 1 field, set the TFTP server address.
Save the changes.