We have a client that want to install a Call Manager Express in a Cisco 2821 router. Between the router and the subnet where we have to connect the IP phones, there is an ASA firewall. Can the IP phones be registered to the CME if they aren't directly connected to the same subnet?
you basically have to open ports on the outside to allow signaling communication with CME from ip phone.
Also, if ip phone is on different subnet then u need to use ip-helper address command to point to tftp server