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Cisco IOS Show Commands: Viewing Configuration, Interfaces, and Device Status

Learn essential Cisco IOS show commands for checking configurations, interfaces, software versions, device status, and troubleshooting information.

Cisco IOS is the command-line operating environment used on many Cisco routers and switches. A show command is an EXEC command that displays operational, configuration, and status information without intentionally changing the device configuration.

Show commands are primarily used for verification and troubleshooting. Configuration commands, such as commands entered from global configuration or interface configuration mode, change how the device operates. Viewing a configuration with a show command does not save, modify, or replace that configuration.

IOS Command Modes and Prompts

Cisco IOS uses command modes to control which commands are available. The prompt helps identify the current mode.

User EXEC mode: Usually shown with a greater-than sign, such as Router>. This mode provides limited monitoring and testing commands.
Privileged EXEC mode: Usually shown with a hash sign, such as Router#. Most administrative show commands are run from this mode.

Use enable to move from user EXEC mode to privileged EXEC mode:

Router> enable
Router#

On devices configured with an enable password or secret, IOS prompts for that credential. The hostname in the prompt may be different, but the ending character is the key distinction: > indicates user EXEC mode and # indicates privileged EXEC mode.

Common Cisco IOS Show Commands

Command	Primary purpose	Information displayed	Typical use case
`show running-config`	Display the active configuration	Hostname, interfaces, addressing, routing, lines, and enabled services	Verify changes currently being used
`show startup-config`	Display the saved boot configuration	Configuration stored in nonvolatile memory	Check what the device will normally load after a reload
`show history`	Display recent commands	Commands retained in the current history buffer	Recall commands during a troubleshooting session
`show ip interface brief`	Provide a concise IPv4 interface summary	Interface names, IPv4 addresses, assignment method, status, and protocol	Quickly verify addressing and link state
`show interfaces <interface>`	Display detailed information for one interface	State, physical details, settings, traffic counters, and errors	Investigate a particular link or interface
`show version`	Display platform and software information	IOS release, model, uptime, memory, boot details, and inventory	Confirm device capabilities and software identity

Viewing the Active Configuration

show running-config

The running configuration is the configuration currently held in memory and used by the device. Display it with:

Router# show running-config

The output commonly includes the hostname, interface definitions, IP addresses, routing settings, access controls, line settings, and enabled services. Configuration changes normally affect the running configuration immediately, so a newly entered setting can change device behavior before it has been saved.

On platforms that support the abbreviation, show run is a shorter form:

Router# show run

Abbreviations work only when the shortened command is unambiguous and supported in the current context. Use the full form in documentation and use ? when uncertain.

Filtering configuration output

Long output can be filtered with a pipe and a filter keyword. Support varies by platform and IOS release.

Router# show running-config | include hostname
Router# show running-config | section interface
Router# show running-config | begin line

include displays lines matching the specified text.
section displays a matching configuration section where supported.
begin starts displaying output at the first matching line where supported.

For example, show running-config | section interface can help locate interface configuration without reading the entire configuration.

Running Configuration Versus Startup Configuration

show startup-config

The startup configuration is the saved configuration stored in nonvolatile memory, traditionally associated with NVRAM. Display it with:

Router# show startup-config

The startup configuration is normally loaded when the device boots. It can differ from the running configuration when an administrator has made changes but has not saved them.

Characteristic	Running configuration	Startup configuration
Location	Active memory	Nonvolatile storage, traditionally NVRAM
When used	Used immediately during normal operation	Normally loaded during boot
Effect of configuration changes	Changes normally take effect immediately	Does not change merely because the running configuration changed
Persistence after reload	Unsaved changes can be lost	Normally persists and is used after reload
Display command	`show running-config` or `show run`	`show startup-config` or `show start`

Comparing these two commands is a basic way to check whether recent changes have been saved. Viewing either file does not save changes. Saving is a separate operation, commonly performed with copy running-config startup-config when appropriate for the network design.

Reviewing Command History

show history

The show history command displays commands retained in the current command history buffer:

Router# show history

History is useful for reviewing recently entered verification or configuration commands and reducing retyping. It is session-specific; it does not provide a permanent audit record of every command ever entered. The number of retained commands can also be limited by the history buffer settings.

Checking Interfaces Quickly

show ip interface brief

show ip interface brief provides a compact, IPv4-focused summary:

Router# show ip interface brief

Typical columns include:

Interface: The physical or logical interface name, such as GigabitEthernet0/0.
IP-Address: The assigned IPv4 address, or a value such as unassigned.
OK?: A platform-dependent indication related to address or hardware information.
Method: How the address was assigned, such as manual configuration or an automatic method.
Status: The interface or physical-layer state.
Protocol: The line protocol, representing the data-link operational state.

The status and protocol columns describe different layers. A useful summary is:

Status	Protocol	Likely meaning	Suggested next check
up	up	The interface and line protocol are operational.	Verify the address, routing, and traffic if connectivity still fails.
administratively down	down	The interface has been disabled with the `shutdown` command.	Review the interface configuration and network design.
down	down	The physical link is not detected or the remote side is unavailable.	Check cabling, transceivers, the correct port, and the remote interface.
up	down	The physical layer is active, but the line protocol is not operational.	Check encapsulation, link-layer compatibility, and the remote configuration.

This command is a fast first check when verifying whether a newly assigned IP address appears on the intended interface and whether the link is operational.

Inspecting One Interface in Detail

show interfaces interface

Use show interfaces with a valid interface identifier to display detailed operational and physical-layer information:

Router# show interfaces gigabitEthernet 0/0
Router# show interfaces gigabitEthernet 0/1

Replace the placeholder with the interface name used by the device. Interface naming differs by platform, so use the name shown by show ip interface brief or context-sensitive help.

The detailed command provides much more information than the brief summary. Common output areas include:

Interface state and line protocol state
Hardware type and MAC address
MTU, bandwidth, and delay
Encapsulation
Configured IP address
Packet and byte traffic counters
Input and output errors
Duplex and speed, where applicable
Interface reset information

Field or counter	What it indicates	Why it matters
Interface and line protocol state	Physical and data-link operational condition	Separates link detection problems from protocol problems
Internet address	IPv4 address configured on the interface	Confirms addressing on the selected interface
MTU	Largest packet size normally accepted without fragmentation	Inconsistent values can contribute to packet delivery problems
Bandwidth	Configured or reported bandwidth value used by some routing calculations	It is not always the same as measured throughput
Duplex and speed	Ethernet negotiation or operational settings	Mismatch or unexpected values can reduce performance or cause errors
Input errors	Problems detected while receiving frames	Increasing values can indicate physical, compatibility, or link-quality issues
CRC errors	Frames that failed a cyclic redundancy check	Often points toward cabling, optics, interference, or other physical-layer problems
Output errors	Problems transmitting frames	Can indicate hardware, congestion, or link problems depending on the platform
Interface resets	Number of times the interface has been reset	Repeated resets may indicate instability or physical-layer trouble

On legacy half-duplex Ethernet, collisions can be significant diagnostic counters. Modern full-duplex links should not normally show collisions. Always interpret counters in context and check whether they continue increasing rather than relying on one historical value.

Checking Software and Hardware

show version

show version reports software, hardware, boot, uptime, and memory information:

Router# show version

Depending on the platform, look for:

The IOS software release and the running IOS image
Device model and processor or hardware identification
Uptime, meaning the time since the device was last restarted
The reason for the last reload
Installed memory information
Interface inventory
Boot image and boot-related details
The configuration register, a boot-related setting reported on many IOS platforms

This command supports inventory collection and basic platform verification. IOS release, model, feature set, and hardware capabilities matter because they affect which commands and features are available and how output is formatted.

Reading IOS Output Effectively

When reading output, identify the structure before interpreting individual values:

Find headings that identify the interface, configuration section, software release, or device component.
Separate fields from their values, such as an IP address, state, MTU, or counter.
Recognize state indicators such as up, down, and administratively down.
Use counters to look for trends and errors, not just isolated numbers.
Compare related fields. For example, read interface status together with line protocol state and error counters.

Router models, switch models, IOS releases, and lab emulators may place fields in different positions or omit platform-specific information. The meaning of a field is more important than its exact output location.

Help, Completion, Abbreviation, and Pagination

Context-sensitive help

Enter a question mark to ask IOS which commands or keywords are valid at the current position:

Router# show ip ?
Router# show interfaces ?

Help is context-sensitive. The results depend on the current command mode, the words already entered, the platform, and enabled features.

Tab completion and abbreviations

Press the Tab key to complete a recognizable command or keyword. IOS also accepts abbreviations when they are unambiguous. For example, show run commonly represents show running-config. If an abbreviation matches more than one command, IOS may reject it or require more characters.

Navigating long output

IOS commonly pauses long output with a message such as --More--. Press the spacebar to display the next page. Press the Enter key to advance one line. A commonly used interrupt sequence for stopping output is Ctrl+Shift+6; platform and terminal behavior can vary.

Filtering output

Where supported, use the pipe operator to restrict output:

Router# show running-config | include ip address
Router# show running-config | exclude shutdown
Router# show running-config | section interface GigabitEthernet0/0
Router# show running-config | begin line

Filtering is especially useful on devices with large configurations. Verify the available filter forms with ? because support and matching behavior can differ.

Safe Verification Workflow

A logical read-only verification sequence is:

Run show version to identify the IOS release, platform, uptime, memory, and available hardware context.
Run show running-config and show startup-config to compare the active and saved configurations.
Run show ip interface brief to review IPv4 addresses and the state of every listed interface.
Use show interfaces <interface-id> on a problem interface to inspect detailed settings, counters, speed, duplex, and resets.
Use filtered configuration output and show history to focus the investigation and recall previous commands.

Show commands are suitable for routine status checks because they are primarily read-only. They do not save configuration changes. A device can therefore show a change in the running configuration while the startup configuration remains unchanged.

Practical Troubleshooting Examples

Verify a newly assigned interface address

Router# show ip interface brief
Router# show interfaces gigabitEthernet 0/0

First locate the interface and address in the summary. Then inspect the detailed output to verify the interface state, line protocol, address, and relevant counters.

Check whether changes have been saved

Router# show running-config
Router# show startup-config

Compare the relevant sections. If a new setting appears only in the running configuration, it is not yet present in the saved boot configuration.

Investigate interface states

An administratively down/down result means the interface has been disabled through configuration. Confirm the state with show interfaces <interface-id> and review its interface section in the running configuration.

A down/down result commonly means that the physical link is not detected or the remote side is unavailable. Check the cable or transceiver, interface type compatibility, the connected port, and the remote interface.

An up/down result means the physical layer is active but the line protocol is not operational. Inspect encapsulation and other link-layer details, then check the remote-side configuration.

Find a missing expected address

If an expected address is absent from the summary, it may not be configured, may be configured on another interface, or may be represented differently on the platform. Check all interfaces with show ip interface brief, search the active configuration, and inspect the intended interface in detail.

Investigate increasing errors

Router# show interfaces gigabitEthernet 0/1

Record input errors, CRC errors, output errors, collisions where applicable, and interface resets. Run the command again later to determine whether values are increasing. Inspect cabling and optics, and verify speed and duplex expectations on both ends. Increasing CRC or input errors often justify a physical-layer investigation.

Resolve command or output differences

If a command from a lab guide is unavailable or output looks different, run show version first. Confirm the platform, IOS release, and feature context. Then use ? to discover the command forms supported by the current device.

Exam-Relevant Notes

Router> indicates user EXEC mode; Router# indicates privileged EXEC mode.
enable enters privileged EXEC mode.
show running-config displays the active configuration in memory.
show startup-config displays the saved configuration normally used at boot.
Unsaved running-configuration changes can be lost after a reload.
In show ip interface brief, up/up indicates an operational interface and line protocol.
administratively down/down indicates an interface disabled with shutdown.
show interfaces provides detailed counters and physical information; show ip interface brief provides a quick summary.
show version identifies IOS software, platform, uptime, memory, boot information, and inventory details.
Use ?, Tab completion, unambiguous abbreviations, pagination controls, and output filters to work efficiently.

For related study, see Cisco IOS show command reference lesson.