Cisco Small Business Switches Face Global DNS Crash Outage
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Network administrators worldwide reported widespread crashes in Cisco small business switches<\/a> on January 8, 2026, triggered by fatal errors in the DNS client service.<\/p>\n Devices entered reboot loops every few minutes, disrupting operations until DNS configurations were removed.\u200b<\/p>\n 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 \u201cwww.cisco.com\u201d and NIST time servers like \u201ctime-c.timefreq.bldrdoc.gov.\u201d<\/p>\n 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.\u200b<\/p>\n Users on Cisco\u2019s community forums reported<\/a> managing dozens of affected devices and performing manual reconfiguration to stabilize them. One administrator noted, \u201cEvery single one crashed today\u2026 until I removed the DNS configuration,\u201d across 50 CBS250 and C1200 units. Similar reports hit Reddit, where SG550X owners confirmed identical symptoms starting simultaneously across sites.\u200b<\/p>\nAffected Software Versions<\/strong><\/h2>\n