The Cisco commands you'll use most in your first week as a network engineer

New engineers often feel they need to memorise the whole command reference. In reality, a small set of show commands answers most day-to-day questions. Learn these first.

Is the port up?

• show ip interface brief: every interface, its IP address and whether it is up or down.
• show interfaces status (switches): port, VLAN, speed and duplex at a glance.

Where is the device?

• show mac address-table: which port a MAC address was learned on. Combine it with the MAC formatter to see the manufacturer.
• show cdp neighbors or show lldp neighbors: what is plugged into the other end.

Is the VLAN right?

• show vlan brief: which access ports are in which VLAN.
• show interfaces trunk: which VLANs are allowed across trunks. A missing VLAN here is a classic cause of "it works on one floor but not the other".

Can it reach the destination?

• show ip route: the router's routing table.
• ping and traceroute: test reachability and find where the path breaks.

What changed?

• show running-config and show logging: the current setup and recent events. Always save a copy before you change anything.

All of these, plus Windows, Linux and Cisco ASA commands, are in the cheat sheets. Keep them open on your phone during your first weeks.