Top 10 Cisco IOS Commands Every Network Engineer Must Knows

Command 1: show running-config

The show running-config command is your go-to for viewing the active configuration of a Cisco device. It displays everything from interface settings to routing protocols currently running. This is especially useful when you're troubleshooting or auditing a network.

• Use Case: Imagine you've inherited a network and need to understand how a router is configured. Running this command gives you a snapshot of the current setup.

Router# show running-config:
Building configuration...
Current configuration : 1234 bytes
!
hostname Router
interface GigabitEthernet0/0
 ip address 192.168.1.1 255.255.255.0
!

Tip: Use show running-config | section interface to filter and display only interface configurations, saving time on large configs.

Command 2: show ip interface brief

This command provides a quick summary of all interfaces, showing their IP addresses, status, and protocol state. It's a lifesaver for checking if interfaces are up or down without digging through detailed output.

• Use Case: You're troubleshooting connectivity issues and want to verify that all interfaces are operational.

Router# show ip interface brief
Interface              IP-Address      OK? Method Status                Protocol
GigabitEthernet0/0     192.168.1.1     YES manual up                    up
GigabitEthernet0/1     unassigned      YES unset  administratively down down

Tip: Look for “down” in the Status or Protocol columns to spot issues like unplugged cables or misconfigurations.

Command 3: configure terminal

The configure terminal command (often shortened to conf t) takes you to global configuration mode, where you can make changes to the device’s settings, like setting IP addresses or enabling routing protocols.

• Use Case: You need to configure a new VLAN or change an interface's IP address.

Router> enable 
Router# configure terminal 
Enter configuration commands, one per line. End with CNTL/Z.
Router(config)# interface GigabitEthernet0/0
Router(config-if)# ip address 192.168.2.1 255.255.255.0

Tip: Always save your changes with write memory to ensure they persist after a reboot.

Command 4: show ip route

This command displays the routing table, showing how the device forwards packets. It's critical for verifying routing protocols like OSPF or EIGRP and checking for correct routes.

• Use Case:You're troubleshooting why a remote network isn't reachable and need to check if the route exists.

Router# show ip route 
Codes: C - connected, S - static, R - RIP, O - OSPF...
Gateway of last resort is not set
C    192.168.1.0/24 is directly connected, GigabitEthernet0/0
O    10.0.0.0/8 [110/2] via 192.168.1.2, 00:01:23, GigabitEthernet0/0
   

Tip: Use show ip route | include 192.168 to filter routes for a specific network.

Command 5: ping

The ping command tests connectivity between devices by sending ICMP echo requests. It's one of the first tools you'll use to diagnose network issues.

• Use Case:You want to confirm if a remote server at 192.168.1.100 is reachable from your router.

Router# ping 192.168.1.100 
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 192.168.1.100, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 1/2/4 ms
            

Tip: Use extended ping (ping with Enter to specify source interfaces) for advanced troubleshooting.

Command 6: traceroute

The traceroute command traces the path packets take to a destination, showing each hop. It's great for pinpointing where connectivity breaks down.

• Use Case:A user reports they can't reach a website, and you need to identify the failing hop.

Router# traceroute 8.8.8.8
Type escape sequence to abort.
Tracing the route to 8.8.8.8
  1 192.168.1.2 4 msec 4 msec 4 msec
  2 10.0.0.1 8 msec 8 msec 8 msec
            

Tip: Asterisks (*) in the output indicate packet loss or a firewall blocking the probe.

Command 7: ip address

The ip address command assigns an IP address and subnet mask to an interface. It's fundamental for setting up network connectivity.

• Use Case: You're configuring a new interface to connect a branch office network.

Router(config)# interface GigabitEthernet0/1
Router(config-if)# ip address 192.168.3.1 255.255.255.0
Router(config-if)# no shutdown
            

Tip: Always use no shutdown to enable the interface after setting the IP address.

Command 8: show vlan brief

On Cisco switches, show vlan brief lists all VLANs, their status, and associated ports. It's essential for verifying VLAN configurations.

• Use Case:You're setting up VLANs for a small office and need to confirm ports are in the correct VLAN.

Switch# show vlan brief
VLAN Name                             Status    Ports
---- -------------------------------- --------- -------------------------------
1    default                          active    Gi0/2, Gi0/3
10   SALES                            active    Gi0/1
20   ENGINEERING                      active    Gi0/4
!

Tip: Check for “active” status to ensure the VLAN is operational.

Command 9: access-list

The access-list command creates Access Control Lists (ACLs) to filter traffic. It's a key tool for network security and traffic control.

• Use Case:You want to block traffic from a specific subnet while allowing others.

Router(config)# access-list 101 permit ip 192.168.1.0 0.0.0.255 any
Router(config)# access-list 101 deny ip 192.168.2.0 0.0.0.255 any
Router(config)# interface GigabitEthernet0/0
Router(config-if)# ip access-group 101 in

Tip: Always test ACLs in a lab (like Packet Tracer) before applying them to production networks.

Command 10: write memory

The write memory (or wr) command saves the running configuration to NVRAM, ensuring changes persist after a reboot.

• Use Case:You've configured a router and want to save your work.

Router# write memory
Building configuration...
[OK]

Tip: Use show startup-config to verify the saved configuration matches the running-config.

Practice These Commands

Conclusion