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Deploying IPv6 in a Cisco UC Environment – Part 4

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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!

Written by Matthew Berry

March 11th, 2011 at 1:22 pm

Posted in Blog

Tagged with ,

4 Responses to 'Deploying IPv6 in a Cisco UC Environment – Part 4'

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  1. Matt,

    Thanks for the post. Im trying to determine how to enable stateless autoconfiguration in CME, and i see this is directly speaking to CUCM. I have searched high and low, but have not had any luck determining how to enable SLAAC. Have you ever done this in CME?



    28 Jun 11 at 9:21 am

  2. MTP is not required for a dual stack IP phone config.

    MTP are required for IPv4-only phone talks to IPv6-Only phone.

    Jay Shah

    1 Apr 12 at 9:35 pm

  3. estimad:

    where should I set the mtp
    How should I configure the MTP
    to call from IPv4 to IPv6


    25 Oct 12 at 12:21 pm

  4. To call IPv4-Only phone to IPv6-Only phone, please follow the follow document @

    Cisco recommends to deploy dual stack devices with ANAT where IPv4 and IPv6 addresses are required per device.

    Jay Shah

    20 Jan 13 at 9:55 am

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