Verification and Troubleshooting

Pipe Filters

Cisco IOS supports piping output through filters to find specific information quickly.

Available Filters

• section: Display configuration section matching a keyword
• include: Show only lines containing a keyword
• exclude: Hide lines containing a keyword
• begin: Start output at the first line containing a keyword
• grep: Pattern matching (Unix-style)
• count: Count the number of lines in output
• head: Display the first N lines
• tail: Display the last N lines

Pipe Filter Examples

# show running-config | section dhcp
# show running-config | include username
# show running-config | exclude !
# show ip route | begin Gateway
# show running-config | count

Device Information

Show IOS Version and System Information

Display IOS version, uptime, hardware model, and configuration register:

# show version

Show CDP Neighbors

Cisco Discovery Protocol (CDP) identifies directly connected Cisco devices:

# show cdp neighbors

For detailed neighbor information including IP addresses:

# show cdp neighbors detail

Show Login Failures

Display failed login attempts:

# show login failures

Show Configuration Sections

View specific configuration sections using pipe filters:

# show running-config | section dhcp
# show running-config | section router
# show running-config | section interface

Interface Status

IPv4 Interface Status

Quick overview of all interfaces (status and IP addresses):

# show ip interface brief

IPv6 Interface Status

Quick overview of all IPv6-enabled interfaces:

# show ipv6 interface brief

Detailed Interface Information

View detailed interface statistics and configuration:

# show interfaces
# show interfaces <interface>

Example:

# show interfaces gigabitEthernet 0/0

Switch Commands

Show Switchport Configuration

Display switchport mode and VLAN information:

# show interfaces <port> switchport

Administrative Mode values:

• dynamic auto: Port attempts to form a trunk if the neighbor is set to trunk or desirable
• dynamic desirable: Actively tries to negotiate trunk formation
• trunk: Port is in permanent trunking mode
• access: Port is in permanent access mode

Example:

# show interfaces fastEthernet 0/1 switchport

Show Trunk Ports

Display all trunk ports and their allowed VLANs:

# show interfaces trunk

Show Spanning Tree Information

View detailed STP information for a specific interface:

# show spanning-tree
# show spanning-tree interface <interface> detail

Example:

# show spanning-tree interface gigabitEthernet 0/1 detail

Show EtherChannel Status

Display EtherChannel summary and member ports:

# show etherchannel summary

For detailed EtherChannel information:

# show etherchannel port-channel

Show VLAN Information

# show vlan brief
# show vlan id <vlan_number>

Show MAC Address Table

# show mac address-table
# show mac address-table interface <interface>

Router Commands

Show Routing Table

Display the complete routing table:

# show ip route

Show Static Routes Only

Display only statically configured routes:

# show ip route static

Show Connected Routes

Display directly connected networks:

# show ip route connected

Show Default Route

Display the gateway of last resort:

# show ip route 0.0.0.0

NAT Commands

Show NAT Configuration

Display NAT configuration:

# show ip nat

Show NAT Translations

Display active NAT translation table:

# show ip nat translations

Show NAT Statistics

Display NAT statistics (hits, misses, pool usage):

# show ip nat statistics

Clear NAT Translations

Remove dynamic NAT entries:

# clear ip nat translation *

EIGRP Commands

Show EIGRP Topology

Display the EIGRP topology table (all learned routes):

# show ip eigrp topology

Show EIGRP Neighbors

Verify EIGRP neighbor adjacencies:

# show ip eigrp neighbors

Key information displayed:

• Neighbor IP address
• Interface connected to neighbor
• Hold time (how long until neighbor is declared dead)
• Uptime
• SRTT (Smooth Round Trip Time)
• Queue count

Show EIGRP Interfaces

Display interfaces participating in EIGRP:

# show ip eigrp interfaces

Show Routing Protocols

Confirm EIGRP configuration and parameters:

# show ip protocols

Show EIGRP Routes in Routing Table

Display only EIGRP routes:

# show ip route eigrp

OSPF Commands

Show OSPF Interface Status

Quick overview of OSPF-enabled interfaces:

# show ip ospf interface brief

For detailed interface information:

# show ip ospf interface
# show ip ospf interface <interface>

Show OSPF Neighbors

Display OSPF neighbor adjacencies:

# show ip ospf neighbor

Key information displayed:

• Neighbor ID (router ID)
• Priority
• State (FULL, 2WAY, etc.)
• Dead time
• Interface
• Neighbor IP address

Show OSPF Routes in Routing Table

Display only OSPF routes:

# show ip route ospf

Show OSPF Database

Display the link-state database:

# show ip ospf database

Show OSPF Process Information

Display OSPF process details, timers, and areas:

# show ip ospf

Network Discovery (CDP)

Cisco Discovery Protocol (CDP) is a Layer 2 protocol that discovers directly connected Cisco devices.

Show CDP Neighbors

Display basic information about directly connected devices:

# show cdp neighbors

Information displayed:

• Device ID (hostname)
• Local interface
• Hold time
• Capability (Router, Switch, etc.)
• Platform (model)
• Remote port ID

Show CDP Neighbors Detail

Display detailed information including IP addresses and IOS version:

# show cdp neighbors detail

Show CDP Status

Check if CDP is enabled:

# show cdp

Show CDP Interface Status

Display CDP status on interfaces:

# show cdp interface

Enable/Disable CDP

(config)# cdp run                  # Enable CDP globally
(config)# no cdp run               # Disable CDP globally

(config-if)# cdp enable            # Enable CDP on interface
(config-if)# no cdp enable         # Disable CDP on interface

DHCP Commands

Show DHCP Bindings

Display current DHCP leases:

# show ip dhcp binding

Show DHCP Pool Statistics

Display DHCP pool utilization:

# show ip dhcp pool

Show DHCP Server Statistics

Display DHCP server statistics:

# show ip dhcp server statistics

Show DHCP Conflicts

Display IP address conflicts:

# show ip dhcp conflict

Access Control List (ACL) Commands

Show All ACLs

Display all configured access lists:

# show access-lists

Show Specific ACL

Display a specific access list:

# show access-lists <number/name>

Example:

# show access-lists 10
# show access-lists BLOCK_TELNET

Show ACL Applied to Interface

Display which ACLs are applied to an interface:

# show ip interface <interface> | include access list

Troubleshooting Commands

Show Running Configuration

Display the current active configuration:

# show running-config

Show Startup Configuration

Display the saved configuration in NVRAM:

# show startup-config

Show Flash Contents

Display files stored in flash memory:

# show flash:
# dir flash:

Show Logging

Display system log messages:

# show logging

Filter logs by severity:

# show logging | include <keyword>

Show Clock

Display system time and date:

# show clock

Show Processes

Display CPU utilization and running processes:

# show processes cpu
# show processes memory

Comparison Commands

Compare Configurations

Compare running configuration with startup configuration:

# show archive config differences

This shows what has changed since the last save.