ARP on Linux: ip neigh, arp, and Neighbor States
The six-state neighbor machine walked live on a real lab, the tunables behind it, and why arp -n cannot show you any of it.
Layer 2
Frames, MAC tables and switching behavior below the IP layer. Articles tagged Layer 2 cover forwarding decisions, trunking, loop prevention and the failure modes unique to switching.
Latest posts
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.
Scapy vs Cisco Layer 2 Defenses: Crafting and Spoofing Packets
Craft spoofed ARP and IP packets with Scapy against a Cisco IOS-XE lab, then watch Dynamic ARP Inspection drop every forgery and name the attacker's real MAC.