CUCM Configuration Parameters for IPv6
Common Device Configuration
CUCM supports two IPv6 devices, IP phones and SIP trunks (to gateways or other clusters). Rather than add IPv6 configuration parameters to specific trunks and phones, a CUCM configuration template contains IPv6-specific configuration parameters for phones and SIP trunks. This section describes that template, which is known as the common device configuration.
There is no default common device configuration profile, and each device is initially associated with a <None> common device configuration. If IPv6 is enabled in the Unified CM cluster with this <None> configuration, IPv6 devices adopt the following settings:
- IP Addressing Mode = IPv4 and IPv6 (essentially “dual-stack”)
- IP Addressing Mode Preference for Signaling = Use System Default
- Allow Auto-Configuration for Phones = Default
If IPv6 is enabled in the Unified cluster, the default phone setting for IP addressing mode is IPv4 and IPv6. If the IP phone supports IPv4 and IPv6, it will adopt this setting, but all IPv4-only phones will ignore this setting.
Cisco recommends IPv4 and IPv6 as the setting for the phone IP addressing mode. IPv6 Only is not recommended for production environments.
Note: When an IPv4 device talks to an IPv6 device, an MTP is required to translate one device’s addressing to a similar IP version.
Allow Auto-Configuration for Phones
This settings essential provides three different options:
On - The Phone is allowed to use Stateless Auto Address Configuration (SLAAC) to acquire an IPv6 address. Whether or not the phone will use SLAAC depends on the link local router’s configuration of the O bit and M bit in Router Advertisements (RAs):
- O bit set (i.e. Stateless DHCP) = The phone will use SLAAC to obtain IP address and will use the DHCP server to acquire other relevant information.
- M bit set (i.e. Stateful DHCP) = The phone will use DHCP alone to acquire relevant information and will not use SLAAC.
- Neither O or M bits are set = The phone will use SLAAC to acquire an IP but will not use DHCP for other information. This option necessitates that the phone also has a TFTP server address configured manually through the phone’s UI.
Off – The phone will not use SLAAC to obtain an IPv6 address. In this scenario, the phone must be configured manually through the phone’s UI or use staeful DHCPv6 to get an IP lease and TFTP information.
Default – The phone will refer to the cluster-wide enterprise setting “Allow Auto-Configuration for Phones.”
IPv6 SIP Trunks and Alternative Network Address Types (ANAT)
Just as with phones, you can modify how SIP trunks use IPv4 and/or IPv6 through a custom CDC. However, the better approach is to define the settings within a custom SIP Profile.
ANAT Behavior with IPv6
Alternative Network Address Types (ANAT) is used in the SIP Offer and Answer exchange by dual-stack SIP trunks. ANAT allows these SIP devices to send both IPv4 and IPv6 addresses in the Session Description Protocol (SDP) body of a SIP Offer, and to return in the SDP body of the SIP Answer a preferred IP address (IPv4 or IPv6) with which to establish a voice connection.
Cisco supports ANAT over dual-stack (IPv4 and IPv4) SIP trunks. ANAT must be supported by both ends of the SIP trunk. You can enable ANAT by checking the Enable ANAT check box on the SIP profile associated with the SIP trunk
Enabling IPv6 in CUCM
Before configuring the cluster-wide parameters in CUCM, you must enable IPv6 on the cluster. This is done through Enterprise Parameters > IPv6 Configuration Modes. Relevant cluster-wide parameters are as follows:
- Enable IPv6 = True / False (default)
- IP Addressing Mode Preference for Media = IPv4 (default) / IPv6
- IP Addressing Mode Preference for Signaling = IPv4 (default) / IPv6
- Allow Auto-Configuration for Phones = On (default) / Off
Once IPv6 is enabled on the cluster, you must go under System > CM Server to manually configure an IPv6 address. Don’t forget this step or IPv6 will not work!