How do I enable Cisco IP Phones in remote office?

I have two Cisco SPA504g IP Phones in my remote office across town that need to connect to the UC520 in my main office. I have a SonicWall TZ180 and a couple PCs in my remote office.

In my main office I have an ASA5505 that provides a site-to-site VPN from one of my vendors. An application on my server requires that particular VPN to connect to my vendor. My server provides DHCP and DNS to my PCs, assigning the ASA5505's address as the gateway. My UC520 provides DHCP to my IP Phones, they are on a different subnet than my PCs. The UC520 is behind the ASA5505, does not run firewall, and connects to my POTS phone lines. The PCs are fine, the IP phones in the main office are fine, all works great.

Can my remote phones connect across the internet to my UC520 in my main office?
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MikeKaneConnect With a Mentor Commented:
You would need a VPN as indicated.  

The phones at the remote office would need to be given the DHCP option 150 from the DHCP server there or they would need a static IP assigned to them with the TFTP server IP set as well.  

I've done this many times with 79XX model phones and Cisco UCM.

Are your phones running SIP or SCCP?    

If your VPN is abstracted away from the physical devices on the network - e.g. if your router is responsible for connecting, authenticating and sending data over the internet via VPN to your other location and the rest of your network doesn't need to worry about it, then yes. The phones should just be able to connect just like any other phone in the local office.

If you need any form of "client software" to initate the VPN connection beforehand - e.g. you need to run a VPN client program on your desktops first - then no, the cisco phones likely won't support initiating that kind of connection. (it's possible they do support one form of VPN or another, but I'd imagine it would be a cisco proprietary vpn system, I'd be willing to put more money on that it won't work)

If your phones can't go throughg VPN, perhaps you can connect to your other location directly by it's external IP address, and forward the appropriate SIP ports for your phones on your router?
My recommendation is put in either an ASA or a Cisco 88x router at your second location. Configure a VPN back to the ASA at your office with the UC520. Make sure you enable the VPN to access your voice subnet.
Make sure the VPN is working properly, ie. you can ping all subnets etc. then configure the DHCP server in the remote office to provide a tftp server and point it to the IP of the UC520.
It should all work once you have done that.
mark_06Connect With a Mentor Commented:
Configure a VPN back to the ASA at your office with the UC520

What I mean is configure a VPN to the ASA - ignore my mention of the UC520 in that line.
Ernie BeekExpertCommented:
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