show mac address-table

Which MAC addresses the switch has learned on which ports.

switching

What it does

The forwarding table. Used to find where a device physically connects, and to spot a MAC appearing on two ports — the signature of a loop or a duplicate address.

Per vendor

PlatformCommand
Cisco IOSshow mac address-table
Cisco NX-OSshow mac address-table
Aruba AOS-CXshow mac-address-table
Juniper JunOSshow ethernet-switching table
MikroTik RouterOS/interface bridge host print

Useful variations

  • Find one deviceshow mac address-table address 001a.2b3c.4d5e
  • Everything on one portshow mac address-table interface Gi1/0/24

Pitfalls

The misreadings that actually cost people time.

  • An entry only exists while the device is talking — a quiet host ages out after five minutes by default.
  • The same MAC flapping between ports means a loop, or two devices sharing an address.
  • Router MACs appear on the uplink, not where the host is; trace hop by hop.

Related

show interfaces statusshow arp