On boot a phone requests the CTL file, then the ITL file. Once these verify, it requests signed configuration files with the .sgn extension.
Checked 2026-10-01
- Vendor
- Cisco
- Product
- Unified Communications Manager
- Subsystem
- TFTP
- Deployment
- on-premises
- Region
- not restricted
- Release range
- 8.0 and later
- Checked
- 2026-10-01
Sources
- Understand CUCM Security By Default and ITL Operation and Troubleshooting — Cisco Systems · tier 2 current vendor documentation · Phone download / ITL verification section (phone console log walkthrough)
Cite this note
APA
WarmTransfer. (2026, October 1). Troubleshooting phone trust and ITL failures in Unified CM: source note cucm-itl-trust-troubleshooting-phone-file-request-order. WarmTransfer. https://warmtransfer.net/knowledge/claims/cucm-itl-trust-troubleshooting-phone-file-request-order
BibTeX
@misc{warmtransfer-claim-cucm-itl-trust-troubleshooting-phone-file-request-order,
title = {Troubleshooting phone trust and ITL failures in Unified CM: source note cucm-itl-trust-troubleshooting-phone-file-request-order},
author = {{WarmTransfer}},
year = {2026},
url = {https://warmtransfer.net/knowledge/claims/cucm-itl-trust-troubleshooting-phone-file-request-order},
note = {Source note cucm-itl-trust-troubleshooting-phone-file-request-order, checked 2026-10-01}
}