Administrator’s Guide for SIP-T4X IP Phones1622. Enter the IP address or any in the Action URI allow IP List field.Multiple IP addresses are separated by commas. If you enter “any” in this field, theIP phone can receive and handle GET requests from any IP address. If you leavethe field blank, the IP phone cannot receive or handle any HTTP GET request.3. Click Confirm to accept the change.Server redundancy is often required in VoIP deployments to ensure continuity of phoneservice, for events where the server needs to be taken offline for maintenance, theserver fails, or the connection between the IP phone and the server fails.Two types of redundancy are possible. In some cases, a combination of the two may bedeployed: Failover: In this mode, the full phone system functionality is preserved by having asecond equivalent capability call server take over from the one that has gonedown/off-line. This mode of operation should be done using the DNS mechanismsfrom the primary to the secondary server. Fallback: In this mode, a second less featured call server (fallback server) with SIPcapability takes over call control to provide basic calling capability, but withoutsome of the advanced features offered by the working server (for example, sharedlines, call recording and MWI). IP phones support configuration of two SIP serversper SIP registration for fallback purpose.Phone Configuration for Redundancy ImplementationTo assist in explaining the redundancy behavior, an illustrative example of how an IP
