Network Nightmare: Cisco Switches Plagued by Reboot Loops Caused by DNS Client Bug

Reports indicate that multiple models of Cisco switches are currently caught in reboot loops due to fatal DNS client errors. The issue, observed by BleepingComputer, stems from a firmware bug affecting the switches’ internal DNS client service.

Starting around 2 AM, the bug manifests as the switches’ DNS client service interpreting DNS lookup failures as fatal errors, leading to continuous reboots of the affected devices.

Devices impacted by this bug are recording fatal errors like the following before initiating reboots:

        DNS_CLIENT - SRCADDRFAIL - Result is 2. Failed to identify address for specified name 'www.cisco.com.', requested addr type 2. ***** FATAL ERROR ***** Reporting Task: DNSC. [debug data] ***** END OF FATAL ERROR *****

        

    

As per reports from administrators reaching out to BleepingComputer, discussions on Reddit, and posts on Cisco Community forum [1, 2], these fatal errors are linked to the DNSC (DNS Client) task and occur when the switches try to resolve “www.cisco.com” and NTP time servers.

Admins have noted that the reboot cycle repeats at short intervals, causing significant disruptions to network operations.

One Reddit user expressed their concern, stating, “The cycle repeats every few minutes. This is obviously pretty disruptive and I’m not going to be able to sustain operations like this for very long.”

Various Cisco switch models, including Cisco CBS250 series, CBS350 series, Catalyst C1200 series, SG350, SG350X, and SG550X series, have been reported to be affected by this bug.

Multiple administrators have highlighted that the failures began simultaneously across different networks, hinting at a global trigger or a time-based condition.

Although Cisco has not officially disclosed the root cause, it has been acknowledged by Cisco support to affect CBS, SG, and Catalyst 1200/1300 switches.

Admins have discovered temporary fixes to halt the reboot loops, such as disabling DNS resolution, SNTP, or time synchronization, and blocking internet access from switch management interfaces.

Disabling DNS configurations has proven effective in stopping the reboot loops, even when DNS servers are operational. Users in Cisco Community forums have also confirmed that removing DNS resolution resolved the issue.

BleepingComputer has reached out to Cisco for a statement and will update the article with additional information as it becomes available.

It’s budget season! Over 300 CISOs and security leaders have shared how they’re planning, spending, and prioritizing for the year ahead. This report compiles their insights, allowing readers to benchmark strategies, identify emerging trends, and compare their priorities as they head into 2026.

Discover how top leaders are translating investment into measurable impact.

Download Now