System Configuration Guide for Cisco Unified Communications Manager, Release 15 and SUs - Configure SRST

Publisher

Cisco Systems

URL

https://www.cisco.com/c/en/us/td/docs/voice_ip_comm/cucm/admin/15/systemConfig/cucm_b_system-configuration-guide-15/cucm_b_system-configuration-guide-14_chapter_01010.html

Published

2026-09-22

Updated

unknown

Accessed

2026-09-24

HTTP status

200

License

Cisco documentation; all rights reserved; no-redistribution; short excerpts and locators only

Source notes citing this source

• Connection Monitor Duration controls how long a phone monitors its restored connection to Unified CM before leaving SRST. It defaults to 120 seconds (maximum 2,592,000) and is set as an enterprise parameter or per device pool to stop phones flapping between SRST and Unified CM. in context
• Unified CM will not delete an SRST reference that is still assigned to a device pool, and a deleted SRST reference cannot be recovered. in context
• The device pool's SRST reference can be Disable (no fallback attempt), Use Default Gateway (the phone's IP default gateway acts as SRST), or a user-defined SRST reference that names a specific gateway. in context
• In Unified CM, an SRST reference is assigned per device pool, and every phone in that pool tries to connect to the assigned SRST gateway when it cannot reach any Unified CM node. in context
• With default settings, a fallback-return test should expect idle phones to stay on the SRST router for about two minutes after the WAN is restored, and phones on active calls to stay until those calls end. inferred in context
• Unified CM's Connection Monitor Duration sets how long a phone watches its Unified CM connection before leaving the SRST gateway. It guards against WAN flapping, defaults to 120 seconds, and can be set cluster-wide or per device pool. in context
• The device pool SRST Reference field in Unified CM has three settings: Disable, Use Default Gateway (the phone's IP gateway acts as the SRST gateway), or a user-defined SRST reference. in context
• In Unified CM, SRST is set per device pool: when a device pool has an SRST reference, its phones try to connect to that SRST gateway if they cannot reach any Unified CM node. in context
• When connectivity to Unified CM returns, phones on the SRST gateway re-register with Unified CM and full telephony service is restored. in context
• The Unified CM SRST task flow runs in this order: configure an SRST reference, assign it to a device pool, optionally set Connection Monitor Duration, then enable SRST on the gateway. in context

Cite this source record

APA

WarmTransfer. (2026, September 22). System Configuration Guide for Cisco Unified Communications Manager, Release 15 and SUs - Configure SRST. WarmTransfer. https://warmtransfer.net/knowledge/sources/cisco-cucm-sysconfig-15-srst

BibTeX

@misc{warmtransfer-cisco-cucm-sysconfig-15-srst,
  title  = {System Configuration Guide for Cisco Unified Communications Manager, Release 15 and SUs - Configure SRST},
  author = {{WarmTransfer}},
  year   = {2026},
  url    = {https://warmtransfer.net/knowledge/sources/cisco-cucm-sysconfig-15-srst},
  note   = {Cisco Systems, accessed 2026-09-24}
}