By Guru Baran
Publication Date: 2026-01-09 05:45:00
Network administrators worldwide reported widespread crashes in Cisco small business switches on January 8, 2026, triggered by fatal errors in the DNS client service.
Devices entered reboot loops every few minutes, disrupting operations until DNS configurations were removed.
The issue surfaced around 2 AM UTC, affecting models like CBS250, C1200, CBS350, SG350, and SG550X series switches. Logs showed DNS_CLIENT-F-SRCADDRFAIL errors failing to resolve domains such as “www.cisco.com” and NIST time servers like “time-c.timefreq.bldrdoc.gov.”
Fatal errors from the DNSC task led to core dumps and automatic resets, with stack traces pointing to DNS resolution failures in firmware versions including 4.1.7.17, 4.1.3.36, and 4.1.7.24.
Users on Cisco’s community forums reported managing dozens of affected devices and performing manual reconfiguration to stabilize them. One administrator noted, “Every single one crashed today… until I…
