Cisco IOS show Commands: Viewing and Verifying Device Status
Learn Cisco IOS show commands for checking configurations, interfaces, VLANs, routing, neighbors, hardware, and troubleshooting device status.
Cisco IOS show commands are EXEC-mode commands that display information about a router or switch. They let you inspect configuration, interface health, VLANs, routing tables, neighbors, hardware, and resource usage without changing device operation.
Use show commands after making a change to confirm that the intended configuration is active and that the device is operating correctly. During troubleshooting, begin with a concise summary and then examine detailed output for the affected feature.
Why show commands matter
- Non-disruptive monitoring: Show commands read device information; they do not normally change configuration or restart services.
- Configuration verification: They reveal whether a command is present in the active configuration and, when applicable, whether it was saved.
- Operational verification: They show whether interfaces, VLANs, trunks, routes, and routing neighbors are actually working.
- Troubleshooting evidence: Counters, protocol states, learned MAC addresses, and routing entries help connect a symptom to a likely cause.
Configuration commands change device behavior. For example, interface GigabitEthernet0/1 selects an interface and shutdown disables it. A show command such as show interfaces GigabitEthernet0/1 only reports the resulting state and statistics.
IOS command modes and syntax
Cisco IOS uses prompts to indicate the current command mode:
| Mode | Typical prompt | Purpose |
|---|---|---|
| User EXEC | Router> | Basic monitoring and limited operational commands. |
| Privileged EXEC | Router# | Full operational verification, including most show commands. |
| Global configuration | Router(config)# | Device-wide configuration changes. |
| Interface configuration | Router(config-if)# | Configuration changes for one interface. |
Enter privileged EXEC mode with:
Router> enable
Router#Most commands in this lesson are run from the # prompt. If you are in a configuration submode, use end or press Ctrl+Z to return to privileged EXEC mode. On many IOS releases, operational commands can also be run from configuration mode by prefixing them with do, such as do show ip interface brief.
Command completion and help
- Press
Tabto complete an unambiguous command or keyword. - Use
?to display context-sensitive help. For example,show ?lists available show categories, whileshow ip ?lists IP-related options. - IOS accepts unambiguous abbreviations. For example,
sh ip int brcommonly meansshow ip interface brief. Full commands are clearer in documentation and exam answers. - If an abbreviation matches more than one command, IOS reports ambiguity rather than guessing.
Pagination
Long output pauses at a --More-- prompt. Press the spacebar for the next page, Enter for one more line, or another available key shown by the device. To disable pagination for the current terminal session, use:
Router# terminal length 0This is convenient when copying output, but it can flood a terminal with lengthy configurations. Restore normal paging with a nonzero value such as terminal length 24; the exact preferred value depends on the terminal.
Viewing active and saved configuration
The running-config is the active configuration held in RAM. It controls the device now. The startup-config is the saved configuration, normally stored in NVRAM and loaded during startup.
Router# show running-config
Router# show startup-config| Comparison | Running-config | Startup-config |
|---|---|---|
| Location | RAM | Normally NVRAM |
| Effect | Active immediately | Used after reload or boot |
| Typical change | Changes as configuration commands are entered | Changes only when the configuration is saved |
| Verification use | Confirm what the device is doing now | Confirm what will be used after restart |
After a change, compare the relevant sections of both outputs. If a command appears in the running configuration but not in the startup configuration, it is active but not saved. A common save operation is copy running-config startup-config, but show commands themselves do not save changes.
Use pipe filters to locate selected sections without reading the entire configuration:
Router# show running-config | section interface GigabitEthernet0/1
Router# show running-config | include ip route
Router# show running-config | section line vty
Router# show running-config | include access-listSystem, IOS, hardware, and resource information
Router# show version
Router# show inventory
Router# show processes cpu
Router# show processes memoryshow version commonly reports the IOS software version, platform and model, uptime, boot image and image location, memory information, configuration register, and boot-related details. The configuration register can affect boot behavior, so it is important when investigating startup or password-recovery issues.
show inventory, where supported, identifies hardware components such as chassis, modules, transceivers, and serial information. The CPU and memory process commands provide basic resource checks. Look for sustained high CPU, unusually high memory use, or a process consuming a disproportionate share of resources. Output fields differ among IOS versions, software trains, and hardware platforms.
Interface status and diagnostics
Use a summary command first:
Router# show ip interface brief
Switch# show interfaces status
Switch# show interfaces descriptionshow ip interface brief provides a concise IPv4 view containing interface names, addresses, administrative status, and line protocol status. On switches, show interfaces status adds a compact view of port state, VLAN, duplex, speed, and media type. show interfaces description is useful for matching operational links to descriptions documented by an administrator.
Use detailed output for one interface or for all interfaces:
Router# show interfaces
Router# show interfaces GigabitEthernet0/1
Router# show controllers GigabitEthernet0/1show interfaces can display physical and line-protocol state, encapsulation, bandwidth, reliability, load, packet and byte counters, queue statistics, duplex and speed, and error counters. show controllers is platform-dependent and can expose lower-level physical details when investigating a suspected hardware or media problem.
Administrative state versus line protocol
The administrative state indicates whether configuration has enabled the interface. The line protocol is the operational protocol state after IOS evaluates physical and data-link conditions.
| Administrative status | Line protocol status | Likely meaning | Next verification command |
|---|---|---|---|
| administratively down | down | The interface is manually disabled, commonly by shutdown. | show running-config | section interface |
| down | down | No usable physical signal, a disconnected cable, a disabled remote end, or incompatible media. | show interfaces interface-id |
| up | down | Physical connectivity exists, but a data-link, encapsulation, keepalive, switching, or protocol condition is failing. | show interfaces interface-id |
| up | up | The interface is enabled and its protocol is operational. | Inspect counters and feature-specific state if traffic still fails. |
Interface counters
| Counter | What it indicates | Common causes | Follow-up checks |
|---|---|---|---|
| CRC errors | Frames failed their integrity check. | Bad cable or optic, interference, faulty hardware, or speed/duplex problems. | Check media, both ends' speed and duplex, and show controllers where supported. |
| Input errors | Errors received by the interface, often including CRC and framing errors. | Physical faults, malformed frames, or duplex mismatch. | Compare counters over time and inspect the remote end. |
| Output drops | Packets were discarded because an output queue could not accept them. | Congestion, bursts, or insufficient interface buffering. | Check utilization, queue statistics, and traffic patterns. |
| Collisions or late collisions | Ethernet transmissions overlapped, primarily relevant to legacy shared or half-duplex links. | Duplex mismatch, faulty media, or obsolete shared Ethernet. | Verify duplex and speed on both ends. |
Run the same interface command at different times. A counter that increases during the reported problem is more useful than a historical nonzero value.
Layer 2 switch verification
| Feature | Command | Expected healthy result | Common fault revealed |
|---|---|---|---|
| VLANs and access assignments | show vlan brief | Required VLAN exists, is active, and expected access ports are listed. | Missing or inactive VLAN, wrong access VLAN, or port in the wrong VLAN. |
| Port mode and membership | show interfaces GigabitEthernet0/1 switchport | Administrative and operational modes agree; access or trunk VLAN values are correct. | Dynamic negotiation result, wrong mode, or unexpected VLAN membership. |
| Trunking | show interfaces trunk | Expected ports are trunking and required VLANs are allowed and active. | Allowed-list, native-VLAN, pruning, or trunk-negotiation problem. |
| MAC learning | show mac address-table | Expected dynamic MAC addresses appear under the correct VLAN and port. | Wrong port, missing learning, flooding, or a possible loop or movement event. |
| Spanning Tree | show spanning-tree | Expected root bridge, forwarding roles, states, and path costs are present. | Unexpected root, blocking port, topology change, or loop-prevention result. |
| EtherChannel | show etherchannel summary | Expected member links are bundled and operational. | Individual, suspended, or mismatched member links. |
show cdp neighbors and show cdp neighbors detail identify directly connected Cisco devices. show lldp neighbors and its detail form provide similar discovery using the vendor-neutral LLDP protocol. Neighbor discovery depends on the protocol being enabled and supported on both sides.
Layer 3 and IP verification
Router# show ip interface
Router# show ip route
Router# show ip route 192.0.2.0
Router# show ip protocols
Router# show arp
Router# show ip arp
Router# show ipv6 interface brief
Router# show ipv6 routeshow ip interface displays IP-related interface details, including protocol state, helper addresses, ACL application, and platform-dependent NAT indicators. Use it when a brief status line is not enough.
show ip route displays the IPv4 routing table. Adding a network or address searches for the route that would be used for that destination, for example show ip route 192.0.2.0.
| Output element | Meaning | Troubleshooting use |
|---|---|---|
| Route code | Source of the route, such as connected, local, static, or a dynamic protocol. | Shows how the device learned the path. |
| Prefix and mask | Destination network and prefix length or mask. | Confirms whether the destination is covered by a route. |
| Administrative distance | Preference for one route source over another. | Explains why one source was selected when multiple sources exist. |
| Metric | Protocol-specific cost used to choose among paths from the same source. | Helps explain path selection within a routing protocol. |
| Next hop | Neighbor router to which traffic is forwarded. | Identifies the next device that must be reachable. |
| Outgoing interface | Local interface used to forward traffic. | Connects the route to interface state and counters. |
| Gateway of last resort | The default route used when no more-specific route matches. | Shows whether unknown destinations have a fallback path. |
Common route codes include C for connected, L for local, S for static, and dynamic-protocol codes such as O for OSPF. The exact legend appears near the beginning of the routing-table output.
show ip protocols reports active routing protocols, advertised and received networks, router ID, timers, passive interfaces, and related settings. show arp or show ip arp displays IPv4 address-to-MAC mappings. For IPv6 networks, use show ipv6 interface brief and show ipv6 route.
Routing-protocol and neighbor verification
Router# show ip ospf neighbor
Router# show ip ospf interface
Router# show ip eigrp neighbors
Router# show ip eigrp topology
Router# show ip bgp summaryFor OSPF, inspect adjacency state with show ip ospf neighbor and interface participation, area, network type, timers, and related details with show ip ospf interface. For EIGRP, use the neighbor and topology commands to examine peer relationships and candidate paths. show ip bgp summary is an awareness-level command for environments using BGP; it summarizes BGP peers and session state.
A missing routing neighbor can explain missing dynamic routes. Check interface state first, then addressing, protocol enablement, area or autonomous-system settings, authentication, timers, network type, passive-interface settings, and filtering.
Filtering and managing show output
The pipe character (|) sends command output through an IOS filter. Filters use a search expression, often a regular expression. Support and exact matching behavior vary by platform and IOS version.
| Filter | Purpose | Example use |
|---|---|---|
include | Display lines matching an expression. | show running-config | include ip route |
exclude | Hide lines matching an expression. | show interfaces | exclude rate |
begin | Start output at the first matching line and continue afterward. | show running-config | begin router ospf |
section | Display a matching configuration section and its related subordinate lines where supported. | show running-config | section line vty |
count | Count matching lines where supported. | show interfaces | count error |
Useful searches include interfaces, routing statements, VLAN references, passwords, ACLs, and protocol configuration:
show running-config | include interface
show running-config | include vlan
show running-config | include password
show running-config | include access-list
show running-config | section router ospfFiltering is a convenience, not a security boundary. Avoid exposing sensitive configuration output unnecessarily, especially when terminal sessions are recorded.
Safe verification workflow
- Define the symptom and intended result. Identify the affected host, interface, VLAN, route, or neighbor.
- Start with a summary. Use
show ip interface brief,show interfaces status, or another concise command. - Verify the interface first. An unavailable interface can invalidate Layer 2, Layer 3, and routing-protocol checks.
- Inspect the relevant feature. Check VLANs and trunks for switching problems, or routes and protocol neighbors for routing problems.
- Compare intended and actual state. Review running configuration, operational state, neighbor state, forwarding information, and counters.
- Check both ends. Link, trunk, duplex, addressing, and routing-protocol problems often require comparing connected devices.
- Record before-and-after output. Capturing relevant commands before and after a change helps prove what changed and whether counters or states improved.
Practical verification examples
Confirm a newly configured interface
Router# show ip interface brief
Router# show interfaces GigabitEthernet0/1
Router# show running-config | section interface GigabitEthernet0/1Confirm the intended IPv4 address, an enabled administrative state, an up/up operational state, expected speed and duplex, and stable error counters.
Confirm a change is active and saved
Router# show running-config | section interface GigabitEthernet0/1
Router# show startup-config | section interface GigabitEthernet0/1The first command verifies the active configuration. The second verifies what will be loaded after a restart. Differences indicate unsaved changes or a configuration mismatch.
Investigate VLAN communication
Switch# show vlan brief
Switch# show interfaces GigabitEthernet0/1 switchport
Switch# show interfaces trunk
Switch# show mac address-tableCheck that the VLAN exists and is active, access ports use the expected VLAN, trunks carry the VLAN, and MAC addresses are learned on expected ports. This sequence helps distinguish an access-port error from a trunk or learning problem.
Verify forwarding to a remote network
Router# show ip interface brief
Router# show ip route 192.0.2.0
Router# show ip arpConfirm that the local interface is operational, a matching route exists, and a directly connected next hop can be resolved in ARP when appropriate. Also consider whether the remote network has a return route.
Check an OSPF neighbor problem
Router# show ip ospf neighbor
Router# show ip ospf interface
Router# show ip protocols
Router# show ip routeDetermine whether an adjacency exists, whether the interface participates in OSPF, whether area and protocol settings are correct, and whether expected learned routes were installed.
Check topology and EtherChannel
Switch# show cdp neighbors detail
Switch# show lldp neighbors detail
Switch# show spanning-tree
Switch# show etherchannel summaryUse neighbor discovery to identify connected devices, Spanning Tree output to see root selection and forwarding or blocking roles, and EtherChannel output to confirm that member links are bundled rather than operating independently.
Troubleshooting patterns
Administratively down/down
The interface is disabled by configuration or intentionally shut down. Run show ip interface brief, then inspect the relevant interface section with show running-config | section interface and look for shutdown.
Down/down
Investigate the cable, optic, transceiver, remote interface, physical signal, and media compatibility. Use detailed interface output and CDP or LLDP when neighbor discovery is applicable.
Up/down
Physical connectivity exists, but the line protocol is not operational. Compare both ends for encapsulation, data-link settings, keepalives, switchport behavior, VLAN configuration, and other protocol-specific requirements.
CRC or input errors increasing
Check cables and connectors, interference, optics, speed and duplex settings, and interface hardware. Repeat show interfaces interface-id to determine whether the counters continue to increase under traffic.
Hosts in a VLAN cannot communicate
Use show vlan brief, the interface-specific switchport command, show interfaces trunk, and show mac address-table. Look for a wrong access VLAN, an absent VLAN, a trunk that does not allow the VLAN, or MAC addresses learned on unexpected ports.
A remote network is unreachable
Search for a matching route with show ip route destination. Then verify the outgoing interface, next hop, interface state, routing protocols, neighbor relationships, and the return path.
Expected OSPF routes are missing
Start with show ip ospf neighbor. If no adjacency exists, inspect show ip ospf interface and show ip protocols for interface participation, area, authentication, network type, timers, passive interfaces, and advertised networks. Finally, check show ip route for installation or filtering symptoms.
Common Cisco IOS show command reference
| Command | Primary purpose | Typical platform or context | Key fields to inspect |
|---|---|---|---|
show version | IOS, platform, uptime, memory, and boot information. | Routers and switches | Version, image, register, uptime, memory |
show running-config | Active configuration | All IOS devices | Interfaces, routing, VLANs, ACLs, access lines |
show startup-config | Saved configuration | All IOS devices | Configuration that will load at startup |
show ip interface brief | Concise IPv4 interface summary | Routers and Layer 3 switches | Address, status, protocol |
show interfaces interface-id | Detailed interface diagnostics | Routers and switches | State, counters, errors, speed, duplex |
show interfaces status | Concise switch-port summary | Switches | Port, status, VLAN, duplex, speed |
show vlan brief | VLAN and access-port verification | Switches | VLAN ID, name, status, ports |
show interfaces trunk | Operational trunk verification | Switches | Native, allowed, active, pruned VLANs |
show mac address-table | MAC learning and forwarding locations | Switches | VLAN, MAC, type, port |
show spanning-tree | STP topology and roles | Switches | Root, role, state, cost |
show ip route | IPv4 forwarding information | Routers and Layer 3 switches | Codes, prefixes, next hops, distance, metric |
show ip protocols | Routing-protocol operation | Routers and Layer 3 switches | Networks, timers, router ID, passive interfaces |
show arp | IPv4 IP-to-MAC mappings | Routers and Layer 3 switches | Address, age, hardware address, interface |
show cdp neighbors / show lldp neighbors | Direct-neighbor discovery | Routers and switches | Neighbor, local port, remote port, platform |
show etherchannel summary | EtherChannel bundle status | Switches with EtherChannel | Group, protocol, member and bundle state |
Related study topics
- Configure Passwords in IOS for protecting EXEC access.
- Configure Trunk Ports for VLAN tagging and trunk verification.
- Configure Router on a Stick for inter-VLAN routing checks.
- Configure OSPF for routing-neighbor and route verification.
- OSI Reference Model for connecting show output to network layers.