Source note · Troubleshooting Cisco IP phones stuck upgrading firmware
PFS uses UDP broadcasts and phone-to-phone TCP child connections on port 4051.
Checked 2026-10-02
- Vendor
- Cisco
- Product
- Cisco Unified IP Phone
- Subsystem
- peer firmware sharing
- Deployment
- on-premises
- Region
- not restricted
- Release range
- third-generation 79xx, firmware 8.3(1) and later
- Checked
- 2026-10-02
Sources
- Cisco IP Phone Feature - Peer Firmware Sharing — Cisco Systems · tier 2 current vendor documentation · How PFS works
Cite this note
APA
WarmTransfer. (2026, October 2). Troubleshooting Cisco IP phones stuck upgrading firmware: source note cucm-phone-firmware-upgrade-troubleshooting-pfs-port-4051. WarmTransfer. https://warmtransfer.net/knowledge/claims/cucm-phone-firmware-upgrade-troubleshooting-pfs-port-4051
BibTeX
@misc{warmtransfer-claim-cucm-phone-firmware-upgrade-troubleshooting-pfs-port-4051,
title = {Troubleshooting Cisco IP phones stuck upgrading firmware: source note cucm-phone-firmware-upgrade-troubleshooting-pfs-port-4051},
author = {{WarmTransfer}},
year = {2026},
url = {https://warmtransfer.net/knowledge/claims/cucm-phone-firmware-upgrade-troubleshooting-pfs-port-4051},
note = {Source note cucm-phone-firmware-upgrade-troubleshooting-pfs-port-4051, checked 2026-10-02}
}