Practical procedure and troubleshooting notes for Common Commands Used for Troubleshooting.
Top 30 Commands used for Troubleshooting with Example Output
# 1. show ip interface brief
# Quick overview of all interfaces and their status
show ip interface brief
# Example Output
Interface IP-Address OK? Method Status Protocol
Gi0/0 192.168.1.1 YES manual up up
Gi0/1 unassigned YES unset administratively down down
Gi0/2 10.10.10.1 YES manual up up
# 2. show interfaces
# Detailed statistics and status for interfaces
show interfaces
# Example Output
GigabitEthernet0/1 is up, line protocol is up
Hardware is Gigabit Ethernet
MTU 1500 bytes
Full-duplex, 1000Mb/s
10000 input packets, 0 CRC errors
# 3. show interfaces status
# Displays switch port state, VLAN, speed and duplex
show interfaces status
# Example Output
Port Status Vlan Duplex Speed
Gi0/1 connected 10 full 1000
Gi0/2 notconnect 1 auto auto
# 4. show running-config
# Displays active configuration in RAM
show running-config
# Example Output
interface GigabitEthernet0/1
switchport access vlan 10
switchport mode access
spanning-tree portfast
# 5. show startup-config
# Displays configuration stored in NVRAM used at next boot
show startup-config
# 6. show version
# Shows IOS version, uptime, hardware model, memory
show version
# Example Output
Cisco IOS Software, Version 15.2
Router uptime is 2 weeks
System image file is "flash:c1900-universalk9"
# 7. show vlan brief
# Displays VLANs and assigned ports
show vlan brief
# Example Output
VLAN Name Status Ports
1 default active Gi0/2
10 SALES active Gi0/1
20 HR active
# 8. show interfaces trunk
# Displays trunk ports and allowed VLANs
show interfaces trunk
# Example Output
Port Mode Encapsulation Status Native vlan
Gi0/1 on 802.1q trunking 1
# 9. show mac address-table
# Displays MAC addresses learned by the switch
show mac address-table
# Example Output
Vlan Mac Address Type Ports
10 0011.2233.4455 DYNAMIC Gi0/1
# 10. show mac address-table address <MAC>
# Finds the switch port associated with a specific MAC
show mac address-table address 0011.2233.4455
# 11. show ip route
# Displays routing table
show ip route
# Example Output
Gateway of last resort is 192.168.1.1
C 192.168.1.0/24 is directly connected, GigabitEthernet0/0
O 10.10.10.0/24 via 192.168.1.2
# 12. show arp
# Shows IP-to-MAC mappings
show arp
# Example Output
Protocol Address Age (min) Hardware Addr Type Interface
Internet 192.168.1.10 2 0011.2233.4455 ARPA Gi0/0
# 13. ping
# Tests network connectivity using ICMP
ping 8.8.8.8
# Example Output
!!!!!
Success rate is 100 percent
# 14. traceroute
# Shows the path packets take to destination
traceroute 8.8.8.8
# Example Output
1 192.168.1.1
2 10.1.1.1
3 8.8.8.8
# 15. show cdp neighbors
# Displays directly connected Cisco devices
show cdp neighbors
# Example Output
Device ID Local Intrfce Holdtme Capability Platform Port ID
SWITCH-2 Gi0/1 153 S I 2960 Gi0/24
# 16. show cdp neighbors detail
# Shows detailed neighbor information including IP
show cdp neighbors detail
# 17. show lldp neighbors
# Displays neighbor devices using LLDP (vendor neutral)
show lldp neighbors
# 18. show spanning-tree
# Displays STP topology and port states
show spanning-tree
# 19. show spanning-tree root
# Displays which switch is the root bridge
show spanning-tree root
# 20. show access-lists
# Displays configured ACLs and match counters
show access-lists
# 21. show ip protocols
# Displays active routing protocols and configuration
show ip protocols
# Example Output
Routing Protocol is "ospf 1"
Router ID 1.1.1.1
# 22. show ip ospf neighbor
# Displays OSPF neighbor adjacency state
show ip ospf neighbor
# 23. show ip eigrp neighbors
# Displays EIGRP neighbors
show ip eigrp neighbors
# 24. show ip bgp summary
# Displays BGP peer status
show ip bgp summary
# 25. show port-security
# Displays switch port security settings
show port-security
# 26. show logging
# Displays system logs and events
show logging
# 27. show processes cpu
# Displays CPU usage by process
show processes cpu
# 28. show interfaces counters errors
# Displays packet errors on interfaces
show interfaces counters errors
# 29. show ip dhcp binding
# Shows DHCP leases assigned to clients
show ip dhcp binding
# 30. show ip nat translations
# Displays NAT translation table
show ip nat translations
Basic System / Device Status
show version
! Displays IOS version, uptime, hardware model, RAM, flash, and license info
show running-config
! Shows the active configuration currently loaded in RAM
show startup-config
! Shows the configuration stored in NVRAM that will load on reboot
show history
! Displays previously entered CLI commands
show clock
! Shows the current system time and timezone
show reload
! Displays scheduled reload information if one exists
show processes cpu
! Shows CPU utilization and processes consuming CPU resources
show processes memory
! Displays memory usage by processes
show users
! Lists users currently logged into the device
show logging
! Displays the system log buffer for errors and events
show tech-support
! Collects extensive troubleshooting info (configs, logs, hardware)
Interface Troubleshooting
show ip interface brief
! Quick overview of all interfaces with IP, status, and protocol state
show interfaces
! Detailed statistics and status for all interfaces
show interfaces status
! Shows switch port status, VLAN, speed, and duplex
show interfaces description
! Displays interface descriptions configured on ports
show interfaces counters
! Shows packet counters for interfaces
show interfaces counters errors
! Displays interface errors like CRC, input errors, drops
show interfaces gigabitEthernet 0/1
! Detailed information about a specific interface
show controllers ethernet-controller
! Hardware-level information about the Ethernet controller
Common Routing Troubleshooting Commands
show ip route
! Displays the routing table
show ip route static
! Shows only static routes
show ip route connected
! Shows directly connected networks
show ip route ospf
! Displays routes learned via OSPF
show ip route eigrp
! Displays routes learned via EIGRP
OSPF EIGRP BGP
show ip ospf neighbor
! Displays OSPF neighbor relationships
show ip ospf interface
! Shows OSPF status and timers on interfaces
show ip ospf database
! Displays OSPF link-state database
show ip protocols
! Shows active routing protocols and their configuration
show ip eigrp neighbors
! Displays EIGRP neighbor routers
show ip eigrp topology
! Shows EIGRP topology table
show ip protocols
! Displays routing protocol configuration
show ip bgp summary
! Shows BGP peer status and session information
show ip bgp neighbors
! Displays detailed BGP neighbor info
show ip bgp
! Displays the BGP routing table
VLAN Troubleshooting
show vlan brief
! Lists VLANs and assigned switch ports
show vlan id 10
! Displays detailed information about VLAN 10
show interfaces trunk
! Shows trunk ports and allowed VLANs
show interfaces switchport
! Displays switchport configuration (access/trunk mode)
show spanning-tree
! Shows STP information for all VLANs
show spanning-tree vlan 10
! Displays spanning-tree details for VLAN 10
MAC Address Table
show mac address-table
! Displays the switch's MAC address table
show mac address-table dynamic
! Shows dynamically learned MAC addresses
show mac address-table interface gi0/5
! Shows MAC addresses learned on a specific port
show mac address-table address 0011.2233.4455
! Finds the port associated with a specific MAC address
ARP Troubleshooting
show arp
! Displays ARP table mapping IP addresses to MAC addresses
show ip arp
! Same function as show arp
clear arp-cache
! Removes all ARP entries so they must be relearned
Spanning Tree Protocol
show spanning-tree
! Displays spanning-tree status and port roles
show spanning-tree root
! Shows which switch is acting as root bridge
show spanning-tree interface gi0/1
! Shows STP state of a specific interface
show spanning-tree blockedports
! Lists ports blocked by spanning-tree
DHCP Troubleshooting
show ip dhcp binding
! Shows IP addresses assigned to clients
show ip dhcp pool
! Displays DHCP pool configuration and usage
show ip dhcp server statistics
! Shows DHCP server packet statistics
show ip dhcp conflict
! Displays IP conflicts detected by DHCP server
clear ip dhcp binding *
! Removes all DHCP leases
NAT Troubleshooting
show ip nat translations
! Displays active NAT translation table
show ip nat statistics
! Shows NAT usage and statistics
clear ip nat translation *
! Removes all NAT entries
Access Control List
show access-lists
! Displays all ACLs configured
show ip access-lists
! Displays IP-based ACLs
show running-config | include access-list
! Searches running config for ACL entries
clear access-list counters
! Resets packet counters for ACL rules
CDP Cisco Discovery Protocol
show cdp neighbors
! Shows directly connected Cisco devices
show cdp neighbors detail
! Displays IP addresses and platform details of neighbors
show cdp interface
! Shows interfaces where CDP is enabled
no cdp run
! Globally disables CDP
LLDP (Vendor Neutral Discovery)
show lldp neighbors
! Shows neighbors discovered via LLDP
show lldp neighbors detail
! Displays detailed neighbor information
Port Security
show port-security
! Displays port security configuration summary
show port-security interface gi0/1
! Shows port security status for specific port
show port-security address
! Displays MAC addresses learned via port security
Debugging Commands
debug ip packet
! Shows packet-level routing information
debug ip icmp
! Displays ICMP packet debugging
debug ip ospf events
! Displays OSPF event activity
debug ip ospf adj
! Shows OSPF neighbor adjacency events
debug ip eigrp
! Displays EIGRP routing activity
debug spanning-tree events
! Shows spanning-tree changes and events
undebug all
! Stops all debugging processes
no debug all
! Alternative command to disable debugging
Clearing Tables / Reset State
clear mac address-table dynamic
! Removes dynamically learned MAC addresses
clear arp-cache
! Clears the ARP table
clear ip route *
! Clears routing table entries
clear counters
! Resets interface packet counters
CLI Filtering
show run | include interface
! Displays lines containing the word "interface"
show run | section interface
! Displays full interface configuration sections
show run | begin router
! Starts displaying output beginning at the word "router"
show ip route | include 10.0.0.0
! Filters routing table entries matching 10.0.0.0