CCNA Study Guide

This tutorial explains Cisco router show commands in detail with example.

Show command is the most powerful command in Cisco IOS. It lists running configuration and provides valuable information for troubleshooting. Information provided by this command will be static. It will not update until we execute the same command again.

We will use Packet Tracer network simulator software for demonstration. Beside Packet Tracer You can also use any other network simulator software such as Boson, GNS or even better if you can afford, use a real Cisco device. No matter what option you choose, till this uses Cisco IOS output will be same.

Create a network topology as illustrate in following figure

show command practice topology

Initial configuration

Device / Interface Connected To IP Address
PC0 Router0's FastEthernet 0/0 10.0.0.2/255.0.0.0
Router0's FastEthernet 0/0 PC0 10.0.0.1/255.0.0.0
Router0's Serial 0/0/0 Router1's serial 0/0/0 50.0.0.1/255.0.0.0
Router1's Serial 0/0/0 Router0's serial 0/0/0 50.0.0.2/255.0.0.0
Router1's FastEthernet 0/0 PC1 20.0.0.1/255.0.0.0
PC1 Router1's FastEthernet 0/0 20.0.0.2/255.0.0.0
  • RIP Routing protocol is configured on both routers.
  • Clock rate and bandwidth is assigned on Router0’s serial interface 0/0/0.

We have created this topology to give you a better overview of show command. You can use single router if you are unable to replicate this topology in packet tracer. Alternatively you can download this pre-configured topology.

Practice topology for show command

No matter what you prefer, for reset of this article I assume that you have at least one router available in workspace.

Access CLI prompt of router

access command prompt in packet tracer

Use enable command to enter in privilege exec mode. Cisco IOS supports unique context sensitive help features. We can use this features to list all available commands and parameters those are associated with show command.

Enter show command with ? ( Question mark ) to list all available commands

show commad help

If prompt returns with parameters excluding <CR> that means it requires more parameters to complete this command.

If prompt returns with <CR> only as option, that means router does not need any additional parameters to complete this command. You can execute this command in current condition.

show command help option

Router#show interfaces

This command shows the status and configuration of interfaces. By default it will display all interfaces. But you can limit it to particular interface. To view the detail of specific interface you can use the following command.

Router#show interface [type slot_# port_#]

For example to view the detail of serial 0/0/0 interface on Router0 we will use following command

show interface command

Output of this command provides several details about interface including its status, encapsulation, interface type, MTU, last input and output packet etc. First line of output shows the status of interface. First up indicates the status of physical layer. Second up refers the data link layer status.

Possible status of physical layer

  • UP: - Interface is receiving physical layer signals.
  • Down:- Interface is not receiving physical layer signals. This could be happen due to following reasons.
    • Cable is unplugged
    • You are using wrong cable type.
    • Attached device is turned off.
  • Administratively down:- Interface is turned off by using shutdown command.

Possible status of data link layer

  • UP:- interface is operational.
  • Down:- interface is not operational. This could be due to following reasons:-
    • Physical layer is down
    • Incorrect encapsulation setting
    • Incorrect clock rate or bandwidth setting
    • Incorrect keepalives setting
Interface status Description
UP and UP Interface is operational
UP and Down Check data link layer for possible reasons given above
Down and Down Check physical layer for possible reasons given above
Administratively down and down Interface is disabled with shutdown command
  • Second line shows the Hardware type and MAC address of interface.
  • Third line shows the IP address of interface.
  • MTU indicates the Ethernet frame size.
  • BW parameter refers to bandwidth link

Router# show ip interface brief

This command provides a quick overview of all interfaces on the router including their IP addresses and status.

show ip interface brief

Router#show controllers [type slot_# port_#]

This command is used to check the hardware statistic of interface including clock rate and cable status such as cable is attached or not. One end of serial cable is physically DTE, and other end is DCE. If cable is attached, it will display the type of cable.

show controller command

Router#show flash

This command will display the content of flash memory, used space and available space. By default router stores IOS image file in flash. We can use this command to check the available space in Flash memory while updating / restoring IOS files.

show flash command

Router#show version

This command will display information about software version of running IOS. It also provides information about configuration setting. It shows current configuration register setting that is used to reset the password of router.

show version command

Router#show startup-config

Routers load configuration from NVRAM in startup. This command will display the configuration stored in NVRAM.

Router#show running-config

Router keeps all running configuration in RAM. This command will display the configuration currently running in RAM.

Router#show clock

This command displays current time on router.

Router#show hosts

This command displays names and addresses of the hosts on the network that you can connect.

Router#show users

This command displays users currently connected to the router.

Router#show arp

This command displays ARP cache table. ARP table is used to resolve the hardware MAC addresses.

Router#show protocols

This command shows the status of configured layer three protocols on the device.

Router#show history

Router keeps a history of used command. This command will list the used command on that level.

Router#show ip route

Routers use routing table to take packet forward decision. This command displays routing table.

show ip router command

Show command supports several other parameters to display command specific information. Due to length of this article we will include them in next articles with their respective topics.

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