System Configuration Guide for Cisco Unified Communications Manager, Release 15 and SUs - Configure Intercluster Lookup Service

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_010100.html

Published

2026-09-22

Updated

unknown

Accessed

2026-09-25

HTTP status

200

License

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

Source notes citing this source

• The ILS Configuration window has an Exchange Global Dial Plan Replication Data with Remote Clusters checkbox, which turns on GDPR data exchange for that cluster. in context
• From Release 15SU5, if the Tomcat server and Tomcat client certificates differ, both certificates must be uploaded to the peer trust store for ILS TLS. in context
• A TLS-authenticated ILS network that exchanged only the Tomcat server certificate may lose peering after an upgrade to 15SU5 or later if a separate Tomcat client certificate is in use. inferred in context
• ILS supports TLS certificate authentication and password authentication, and the two can be used together. in context
• An ILS network supports up to 10 hub clusters with 20 spoke clusters per hub, to a maximum of 200 clusters in total. in context
• In an ILS network, hub clusters form the backbone and use automesh to build a full mesh among themselves. in context
• Cisco cautions that hub clusters need enough CPU to handle the ILS load of their spokes. in context
• Third-party systems cannot connect directly to an ILS network. in context
• An ILS spoke cluster can have only one hub cluster. in context
• The ILS service runs only on the Unified CM publisher node. in context
• The Intercluster Lookup Service (ILS) lets remote Unified CM clusters form a multi-cluster network that shares data, without an administrator configuring each connection between clusters by hand. in context
• The ILS Remote Cluster configuration covers services for remote clusters such as Extension Mobility Cross Cluster, TFTP and RSVP Agent. in context
• An ILS spoke cluster connects only to its local hub cluster and never contacts other hub or spoke clusters directly. in context
• Cisco's ILS task flow is: configure Cluster IDs, configure ILS starting with the hub cluster, verify that ILS is running, then configure the Remote Cluster view. in context
• If you choose TLS authentication for ILS, the Release 15 guide says you must also exchange CA-signed certificates between the nodes. in context
• Every cluster in an ILS network needs a unique Cluster ID, and ILS does not work if remote clusters keep the default Cluster ID StandAloneCluster. in context
• To check that ILS is running, look at the ILS Clusters and Global Dial Plan Imported Catalogs section under Advanced Features > ILS Configuration on a cluster's publisher. in context
• In Unified CM 15, an ILS network supports up to 10 hub clusters with 20 spoke clusters per hub, up to 200 clusters in total. in context

Cite this source record

APA

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

BibTeX

@misc{warmtransfer-cisco-cucm-sysconfig-15-ils,
  title  = {System Configuration Guide for Cisco Unified Communications Manager, Release 15 and SUs - Configure Intercluster Lookup Service},
  author = {{WarmTransfer}},
  year   = {2026},
  url    = {https://warmtransfer.net/knowledge/sources/cisco-cucm-sysconfig-15-ils},
  note   = {Cisco Systems, accessed 2026-09-25}
}