show interface
Displays the status and configuration of all interfaces or a specified interface on a Cisco Nexus switch.
Overview
The 'show interface' command is a fundamental diagnostic tool on Cisco Nexus switches running NX-OS. It provides a comprehensive view of the operational status, configuration, and performance statistics for any interface. This command is essential for network engineers to verify connectivity, troubleshoot issues, and monitor interface health. The concept behind it is to expose the state of the physical and logical layers of the network interface, including line protocol, speed, duplex, errors, and traffic rates. On NX-OS, the output is similar to Cisco IOS but includes additional fields such as 'Rate mode' (dedicated or shared) and 'EtherType'. It is used in initial troubleshooting workflows: when a user reports connectivity problems, the first step is often 'show interface' to check if the interface is up/up. If down, the engineer can check admin state, cabling, or negotiate issues. The command also helps in capacity planning by showing utilization trends. NX-OS specific behavior includes support for virtual interfaces like VLAN interfaces (SVI) and port-channels, which also appear in the output. The command can be filtered with keywords like 'brief', 'status', or 'counters' to focus on specific aspects. Overall, mastering this command is critical for any Cisco network professional.
show interface [interface-type slot/port] [brief | description | status | capabilities | transceiver | counters | mac-address | flow-control | priority-flow-control | preempt | storm-control | trunk | switchport | vrf]When to Use This Command
- Verify interface operational status (up/down) and speed/duplex settings after a configuration change.
- Troubleshoot connectivity issues by checking input/output errors, CRC errors, and packet drops.
- Monitor interface bandwidth utilization and packet counts for capacity planning.
- Validate VLAN membership and trunking status on switchport interfaces.
Parameters
| Parameter | Syntax | Description |
|---|---|---|
| interface-type slot/port | ethernet slot/port | mgmt slot/port | vlan vlan-id | port-channel channel-number | Specifies a particular interface to display. If omitted, all interfaces are shown. For example, 'ethernet 1/1' or 'vlan 10'. |
| brief | brief | Displays a summary table of all interfaces with key fields: status, VRF, IP address, speed, and port-channel membership. |
| status | status | Shows interface status in a compact format, including line protocol, admin state, and description. |
| counters | counters [errors | detailed | module slot] | Displays packet counters and error statistics. Use 'errors' to see only error counters, 'detailed' for more granular data. |
Command Examples
Basic interface status check
show interface ethernet 1/1Ethernet1/1 is up
admin state is up, Dedicated Interface
Hardware: 100/1000/10000 Ethernet, address: 0011.2233.4455 (bia 0011.2233.4455)
Description: Link to Core-SW1
Internet Address is 10.1.1.1/24
MTU 1500 bytes, BW 10000000 Kbit, DLY 10 usec
reliability 255/255, txload 1/255, rxload 1/255
Encapsulation ARPA, medium is broadcast
Port mode is access
full-duplex, 10000 Mb/s, media type is 10G
Beacon is turned off
Auto-Negotiation is turned on
Input flow-control is off, output flow-control is off
Auto-mdix is turned off
Rate mode is dedicated
Switchport monitor is off
EtherType is 0x8100
EEE (Energy Efficient Ethernet): n/a
Last link flapped 2week(s) 3day(s)
Last clearing of "show interface" counters never
5 minutes input rate 1,234,567 bits/sec, 456 packets/sec
5 minutes output rate 987,654 bits/sec, 321 packets/sec
12345678 packets input, 987654321 bytes
Runts 0, Giants 0, CRC 0, No Buffer 0
Input error 0, Frame 0, Overrun 0, Ignored 0
87654321 packets output, 123456789 bytes
Underrun 0, Output error 0, Collisions 0, Late Collisions 0
deferred 0, Lost Carrier 0, no buffer 0
Interface resets 0, Instance resets 0First line shows interface is up. Admin state is up. Hardware details include MAC address. Description is set. IP address assigned. MTU 1500. Bandwidth 10 Gbps. Reliability 255/255 (perfect). Load averages low. Full duplex, 10 Gbps. Last link flapped 2 weeks ago. Input/output rates show current utilization. Packet counts and error counters: all zeros indicate no errors.
Brief summary of all interfaces
show interface briefInterface Status VRF IP Address Speed Port Channel Eth1/1 up default 10.1.1.1/24 10G -- Eth1/2 down default unassigned 10G -- Eth1/3 up default 192.168.1.1/24 1G -- mgmt0 up default 10.10.10.1/24 100M --
Shows each interface, its status (up/down), VRF, IP address, speed, and if it's part of a port-channel. Useful for a quick overview.
Understanding the Output
The 'show interface' output provides a wealth of information about the physical and operational state of an interface. The first line indicates the line protocol status: 'up' means the interface is operational, 'down' indicates a problem (e.g., cable unplugged, administrative shutdown). The admin state shows if the interface is administratively enabled. The hardware section lists the MAC address, description, IP address, MTU, bandwidth, and delay. Reliability is a ratio out of 255; 255/255 is perfect, lower values indicate errors. Txload and rxload show utilization as a fraction of 255; values above 200/255 indicate high utilization. Duplex and speed should match the connected device; mismatches cause errors. Error counters like CRC, runts, giants, and input/output errors indicate physical layer issues; any non-zero values warrant investigation. The 5-minute input/output rate gives real-time bandwidth usage. Healthy interfaces show no errors and appropriate speed/duplex. Problematic interfaces show errors, flapping, or speed/duplex mismatches.
Configuration Scenarios
Verifying a new access port configuration
A new server is connected to Ethernet1/5, configured as an access port in VLAN 100.
Topology
[Server] --- Eth1/5 [Nexus]Steps
- 1.Configure interface Ethernet1/5 as access port in VLAN 100.
- 2.Use 'show interface ethernet 1/5' to verify status and VLAN.
! Configuring access port interface ethernet 1/5 switchport mode access switchport access vlan 100 no shutdown
Verify: Verify with 'show interface ethernet 1/5' that status is 'up', port mode is 'access', and VLAN is 100. Also check 'show vlan id 100' to confirm the interface is listed.
Watch out: If the interface shows 'down/down', check the server NIC and cable. If 'admin down', ensure 'no shutdown' was applied.
Troubleshooting with This Command
When troubleshooting connectivity issues on a Nexus switch, 'show interface' is the starting point. Begin by checking the interface status: if it shows 'down', the issue is physical (cable, transceiver, or peer device). If 'up' but errors are present, examine the error counters: CRC errors suggest cabling or duplex mismatch; runts/giants indicate speed mismatch; input/output errors may point to hardware faults. Use 'show interface counters errors' to isolate error types. For high utilization, compare the 5-minute input/output rate to the interface bandwidth; sustained rates above 80% may require link aggregation. If the interface is up but no traffic passes, verify VLAN membership with 'show interface switchport'. For trunk ports, ensure allowed VLANs include the necessary ones. Also check for interface flapping by looking at 'Last link flapped' timestamp; frequent flapping indicates unstable physical connection. On NX-OS, you can also use 'show interface status err-disabled' to find interfaces disabled due to errors. Always correlate with logs using 'show logging last 10' to see if errdisable events occurred. For performance issues, use 'show interface counters detailed' to see unicast, multicast, and broadcast packet counts. Broadcast storms can be identified by excessive broadcast packets. In summary, systematic use of 'show interface' and its variants pinpoints most Layer 1/2 problems.
CCNA Exam Tips
Memorize that 'show interface' is the first command for troubleshooting Layer 1/2 issues; look for 'up/up' status.
Know that CRC errors often indicate cabling or duplex mismatch; runts/giants suggest speed mismatch.
Understand that 'show interface counters' provides detailed error statistics; useful for identifying non-stop forwarding issues.
Common Mistakes
Assuming 'up' means fully operational without checking duplex/speed mismatches.
Ignoring non-zero error counters; even small numbers can indicate intermittent issues.
Forgetting to use 'show interface brief' for a quick overview, instead parsing full output for each interface.
Platform Notes
On Cisco NX-OS, 'show interface' output includes fields not present in IOS, such as 'Rate mode' (dedicated or shared), 'EtherType', and 'EEE' status. The 'brief' option is similar but the output format may differ slightly. For virtual interfaces like VLAN interfaces (SVIs), the command works the same. On Nexus, you can also use 'show interface transceiver' to check optical parameters. Equivalent commands on other platforms: Juniper uses 'show interfaces terse' for brief output; Arista uses 'show interfaces status'. NX-OS also supports 'show interface description' to display only descriptions. Version differences: In NX-OS 7.x and later, the output includes 'Auto-mdix' and 'Beacon' fields. Always check the specific NX-OS version documentation for exact syntax.
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