Esip connections


Im hoping that someone here has dealt with this current situation before. Currently, my employer decided to 86 the Cisco CME setup that we have currently enjoyed problem free for quite sometime. This system was replaced with an Asterisk IP PBX system that is not an appliance. The PRI’s were replaced with ESIP. The carrier provided a managed router at the facility, handing off ESIP circuit & NBS signalling on one interface. This carrier also asked that we provide an internal private IP address to them from my voice vlan, so that they can configure this interface with that IP, which will be the ESIP gateway. The PBX is connecting to the network via the one NIC interface provided and it has an IP on the voice vlan. Instead of terminating the carrier’s router interface to my LAN switch, I would like to terminate the interface to my router/firewall. Currently the system works fine, all routes have been configured correctly and I have voice communication local and remote. Why would the carrier insist on providing them with an IP off of my internal network to create ESIP gateway instead of them providing an IP address that I can terminate at the router and configure appropriately?