IPv6 Stack Overview
IPv6 is an expanded IP addressing protocol that uses 128 bits instead of the 32 bits that IPv4 addresses use. IPv6 provides a much broader range of IP address than IPv4, which greatly reduces the risk of IP address exhaustion, which is among the main concerns with IPv4 addressing.
By default, Cisco Unified Communications Manager is configured to use IPv4 addressing. However, you can also configure the system to support the IPv6 stack thereby allowing you to deploy a SIP network with IPv6-only endpoints. In addition to reducing the risk of IP address exhaustion, IPv6 provides some of the following benefits:
Stateless address autoconfiguration
Simplified multicasting functionality
Simplified routing, minimizing the need for routing tables
Delivery of services optimization
Better handling of mobility
Greater privacy and security
IPv6 at the System Level
If you are deploying an IPv6 network, the Cisco Unified Communications Manager server still uses IPv4 for some internal communications. This is because some internal system components and applications support only IPv4. As a result, even if all of your devices operate in IPv6-only mode, the Cisco Unified Communications Manager server will still have both an IPv4 and IPv6 address as the server must use IPv4 for some internal communications.
If you need your SIP devices to operate in both IPv4 and IPv6 networks, you will need to configure two stacks. After you complete the tasks in this chapter to enable the IPv6 stack in Cisco Unified Communications Manager, you will then have to also enable your SIP network for two stacks. See Two Stacks (IPv4 and IPv6) Overview.