An administrator troubleshoots a DNS issue with Cisco UCM and observes that the hostname resolution returns the wrong IP address The DNS team Informs…

Cisco UCM keeps a local DNS host-lookup cache so that repeated queries do not always reach the external DNS server.

When an A/AAAA record is changed on the DNS server, UCM will continue to hand out the stale address until its cache entry is purged.

The CUCM CLI command

utils network name-service hosts cache invalidate

immediately removes every cached host entry, forcing the next resolution attempt to query the authoritative DNS server and pick up the new IP address.

No ARP information or DNS-server restart is required, and the sub-command validate merely verifies cache consistency; it does not clear the cache.

B. ARP entries map IP→MAC on the local LAN; they do not affect DNS name resolution.

C. The sub-command “validate” checks cache integrity—it does not flush or rebuild it.

D. Restarting the external DNS server does not clear the already stored cache inside CUCM.

1. Cisco Unified Communications Manager Command Line Interface Reference Guide, Release 14—Section “utils network name-service hosts cache”, pp. 431-432: “invalidate—Removes all host entries from the cache so that subsequent lookups query DNS.”

2. Cisco Unified Communications Operating System Administration Guide, Release 12.5(1)—Chapter “DNS and Hostname Resolution”, p. 129: “To refresh DNS information on the node, issue utils network name-service hosts cache invalidate from the CLI.”

3. Cisco Collaboration SRND 12.x—Section 12.2.2 “DNS Considerations”: “CUCM caches host lookups; use the invalidate sub-command to clear stale entries after DNS record changes.”