cisco onprem uc · published

Planning a Unified CM upgrade

Verified 2026-09-25 · 60 sources · tier 2

Planning an upgrade for Cisco Unified Communications Manager (Unified CM) requires validating virtualization prerequisites, adhering to supported target releases, and maintaining node sequencing across dependent components 594229. Cisco treats an upgrade as complete only when every node has installed the inactive software version, switched active versions, rebooted, and finished database replication 57.

Supported upgrade paths and deployment requirements

There are no Direct Refresh Upgrade paths to Unified CM and IM and Presence Service Release 15 or later 36. Refresh upgrades from source releases earlier than 12.5.x to Release 15 or later are unsupported 35. Additionally, upgrading from Release 14SU4 to any destination lower than 15SU2 is unsupported 1. Any supported path using a PCD Upgrade Task or PCD Migration Task requires Prime Collaboration Deployment Release 15 37.

Release 15x supports only virtualized deployments and does not support bare-metal servers 59. A direct upgrade to Release 15 fails on any single-80GB-vDisk deployment, even when the virtual disk has been manually resized to 110 GB 2. Starting in Release 15SU3, ESXi virtual machines must utilize a CPU mode supporting AVX, requiring administrators to verify VMware Enhanced vMotion Compatibility (EVC) settings 4.

Version 12.5 on-premises calling applications (Unified CM, SME, IM and Presence, CER, Unity Connection, and Paging Server) reached End of Software Maintenance Releases on 31 August 2024 and Last Date of Support on 31 August 2025 2221.

Pre-upgrade tasks and system preparations

Cisco strongly recommends running the Upgrade Readiness COP file prior to a Release 15 upgrade, though it is not mandatory 45. Any required COP file must be installed on every node across the cluster before starting the upgrade, regardless of whether PCD or Unified OS Administration is used 9.

The common partition requires at least 25 GB of free space before upgrading, although Cisco warns that an upgrade can still fail with an insufficient-space error even when 25 GB is free 8. Installing the Free Common Space COP file makes the inactive partition unusable, which permanently removes the option to switch back to the prior version 26.

Before beginning maintenance, perform the following tasks:

Take a fresh Disaster Recovery System (DRS) backup, as Cisco cautions that outdated backups risk data loss or unrecoverable states 27.
Add a virtual serial port to each virtual machine so installation logs can be dumped if failures occur, and remove it following the upgrade because it affects VM performance 51.
Record registered device counts (phones, gateways, media resources) in Cisco Unified Real-Time Monitoring Tool (RTMT) and assigned-user counts in IM and Presence to compare post-upgrade 46.
Take screenshots of IM and Presence and Unified CM enterprise parameters, as differing values can result in IM and Presence parameters being overwritten by Unified CM values 20.
Disable High Availability on each Presence Redundancy Group and stop the Cisco Sync Agent on IM and Presence 28.
On systems with Permanent License Reservation (PLR), return the license via license smart reservation return before upgrading to Release 15 39.
Suspend LDAP user synchronisation and enforce a strict configuration freeze; Cisco states that modifications made during the upgrade—including automated jobs, password adjustments, and LDAP syncs—are overwritten 3455.

Endpoint and license planning

Phone hardware and firmware must be validated prior to target software installation:

Cisco Wireless IP Phone 8821 and 8821-EX models require firmware 11.0(5)SR3 or later before Unified CM is upgraded to Release 15 3.
Devices on Cisco's deprecated phone list stop operating following an upgrade to the current Unified CM release and must be replaced prior to upgrading 16.
End-of-Life phone models are not tested by Cisco with Unified CM Release 15x 23.

Following installation, Unified CM operates in a 90-day evaluation period, after which the creation of new users and devices is blocked until registration with Cisco Smart Software Manager (CSSM) or a CSSM satellite completes 53. Smart License authorizations remain valid for 90 days, renewing at least once every 30 days; expirations prevent new provisioning 52. Call Home is deprecated as a transport starting in Release 15SU2, making Smart Transport (introduced in 14SU4 and 15SU2) the preferred mechanism 6.

Phones maintain cluster security via an Initial Trust List (ITL) file containing the ITLRecovery certificate, TFTP CallManager certificate, CAPF certificate, and TVS certificates 32. Administrators should maintain an offline copy of the ITL Recovery key via file get tftp ITLRecovery.p12 alongside DRS backups, as it is required to recover phones that reach an untrusted state 33. If endpoint trust is lost, executing utils itl reset localkey or utils itl reset remotekey generates a new ITL recovery file to restore communication 31. Setting the enterprise parameter "Prepare Cluster for Rollback to pre-8.0" distributes an ITL with empty TVS and TFTP sections so phones accept unsigned configuration files and alternate ITLs 41.

Sequencing and node execution

Standard deployments mandate that Unified CM and IM and Presence run identical releases; mismatched versions are not supported, though centralized deployments may mix them 29. Cisco's Collaboration Systems Release (CSR) Compatibility Matrix identifies cross-product software compatibility for CSR 10.5 and onward for applications like Unity Connection, Cisco Emergency Responder, and Expressway 10.

Cluster node transitions must proceed in order:

The Unified CM publisher is upgraded and switched active first, followed by the subscriber nodes 42.
Version switching must be completed on all Unified CM nodes prior to switching versions on any IM and Presence node 56.
After the upgrade, re-enable High Availability on Presence Redundancy Groups, restart the Cisco Sync Agent, and resume LDAP user synchronisation 2855.

When performing an L2 upgrade on a Cisco Unity Connection cluster, the publisher node is fully disabled while the subscriber continues handling traffic 12. Administrators must not switch versions or restart the Unity Connection publisher until the subscriber upgrade has completed 11. Unity Connection nodes are then switched active by switching the publisher first, followed by the subscriber 11.

Rollback and disaster recovery considerations

Version switching places new software onto an inactive disk partition, enabling rollback, which Cisco supports with most direct upgrades but not with migrations 58. WarmTransfer's reading of the sources is that a version-switch rollback window exists only while the prior release remains intact on the inactive partition; following a migration, data-import fresh install, or Free Common Space COP installation, reverting requires reinstalling the base release and restoring a matching DRS backup 30. For Unity Connection, rolling back to a previous version prevents subsequent forward switching to the newer partition and requires reinstalling the upgrade 13.

Disaster Recovery System restores cannot cross software versions and must be executed on the identical product version as the backup archive 19. DRS restores additionally require matching the host IP address, hostname, DNS setup, and deployment type against the parameters stored inside the backup 18. If the cluster security password was modified following the backup event, the restore operation fails unless the original password is known 17.

Applicability

Applies to: Cisco Unified Communications Manager, Cisco Prime Collaboration Deployment, Cisco IM, Cisco Unified Communications Manager 12.5, Cisco Unity Connection, and Cisco Collaboration Systems Release. Deployments: on-premises. Sources checked 2026-09-25.

What remains uncertain

Whether specific hardware server models outside virtualized environments can run diagnostic rollback tools is not covered by the sources below.