Port Security — Sticky MACs & Violation Modes

Per access port: learn/limit MACs, act on violations. Default violation mode is shutdown (err-disable); protect drops silently, restrict drops and logs. interface Gi1/0/1 switchport mode access switchport port-security switchport port-security maximum 2 switchport port-security mac-address sticky switchport port-security violation shutdown switchport port-security aging time 10 type inactivity Sticky converts learned MACs into config — survives […]

How a Switch Learns (CAM Table)

A switch builds its MAC (CAM) table by learning the source MAC of every incoming frame, then forwards on the destination MAC. Receive frame Learn: source MAC → ingress port Lookup: destination MAC in table Forward (known unicast) or flood (unknown unicast, broadcast, and multicast by default) within the VLAN Frame type Switch action Known […]

EtherChannel & LACP

EtherChannel bundles multiple physical links into one logical Port-Channel: more bandwidth, redundancy — and one STP link instead of several. Hardware rules All member links same speed; up to 16 configured, max 8 active per port-channel (rest standby). Protocols & negotiation Mode pair PAgP (Cisco) LACP (802.3ad) desirable/desirable · desirable/auto · active/active · active/passive ✅ […]

Collision vs Broadcast Domains

Collision domain: where frames can collide (only relevant for half-duplex). Broadcast domain: where broadcasts (ff:ff:ff:ff:ff:ff) get forwarded. Collision domain A network segment where two devices can transmit simultaneously and cause collisions. OSI layer: L1/L2. Technology: Ethernet (CSMA/CD — historical). Hub → one big collision domain Switch → one collision domain per port Router → separates […]