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Native VLAN Mismatch: Read the CDP Log, Fix the Trunk
%CDP-4-NATIVE_VLAN_MISMATCH hands you both interfaces and both native VLANs in one line. The real damage is underneath it: untagged frames get re-homed at the trunk boundary and two VLANs quietly become one. Captured live on IOS XE 17.18.2 in CML.
Errdisable Recovery on Cisco: Every Cause and How to Bring the Port Back
An err-disabled port stays down forever by default, because nothing auto-recovers until you arm it. The full cause list from IOS XE 17.18.2, how to identify which one fired in ten seconds, and the captured proof that auto-recovery is a retry loop rather than a fix.
MAB with FreeRADIUS on Cisco: MAC Authentication Bypass Without ISE
MAB with no ISE node and no licence: FreeRADIUS 3.2.7 against a Catalyst 9000v, with the freeradius -X trail that proves MAB is bare PAP, the MAC format everyone gets wrong, and a real Method: mab / Authc Success on a live switchport.