In the early hours of January 8, 2026, network administrators worldwide began reporting continuous reboot loops affecting multiple Cisco switch models. The incident was not caused by a cyberattack, but by a firmware defect in the embedded DNS client (DNSC) service. The switch will use this information but not the clients behind it. After this we have the same issue and can only resolve this by resetting. This guide covers CLI commands for setting up DHCP pools, excluding addresses, defining default gateways and DNS servers, and configuring switch DNS. It also provides verification, troubleshooting, and best practices for global IT professionals and SMBs. Part 1: Cisco Switch DNS and DHCP. Hi, Are there any recommendations for configuring DNS servers in the core switch? Is it better to configure. We already rebooted both. Multiple Cisco switch models are suddenly experiencing reboot loops after logging fatal DNS client errors, according to reports seen by BleepingComputer.
[PDF Version]