Cisco Switches Hit by Reboot Loops Due to DNS Client Bug

Why It Matters

The reboot loops can halt enterprise network operations, forcing administrators to apply work‑arounds while Cisco develops a patch, highlighting the risk of firmware bugs in core infrastructure.

Key Takeaways

• DNS client bug triggers fatal errors, causing reboots
• Affects multiple Cisco CBS, SG, and Catalyst switch lines
• Work‑around: disable DNS, SNTP, or internet access
• Cisco has acknowledged issue but no fix yet
• Repeated reboots severely disrupt network services

Pulse Analysis

The sudden emergence of a DNS client bug across a broad swath of Cisco’s entry‑level and mid‑range switches underscores how a single firmware flaw can cascade into widespread network outages. The fatal "SRCADDRFAIL" error, logged just before each reboot, originates from the DNSC task when the device fails to resolve common names such as www.cisco.com or NTP servers. Because the error is treated as unrecoverable, the switch initiates an automatic reboot cycle, repeating every few minutes and effectively removing the device from the network fabric.

For IT teams, the immediate priority is restoring stability while awaiting an official firmware update. Disabling DNS resolution on the affected switches has proven effective, as has turning off SNTP or blocking outbound traffic from management interfaces. These mitigations, however, come at the cost of losing automated name resolution and time synchronization, which can complicate network management and monitoring. Cisco’s acknowledgment of the problem without a public timeline for a fix adds pressure on organizations to assess risk, apply temporary configurations, and possibly roll back to earlier, stable firmware versions.

The incident serves as a cautionary tale about the importance of rigorous pre‑deployment testing and rapid patch distribution for critical networking gear. Enterprises should maintain a robust change‑control process, including staged firmware rollouts and comprehensive health monitoring, to detect anomalies like repeated reboot loops early. As Cisco works toward a permanent resolution, administrators are advised to document all temporary work‑arounds, keep firmware inventories up to date, and engage Cisco support proactively to ensure they receive the forthcoming patch as soon as it is released.