show interface brief
Displays a summary of all interfaces on the switch, including their status, protocol, and basic configuration.
Overview
The 'show interface brief' command is a fundamental tool for any network engineer working with Cisco Nexus switches. It provides a high-level summary of all interfaces on the device, displaying their operational status, administrative state, speed, duplex, VRF membership, and interface type. This command is typically the first step in troubleshooting connectivity issues, as it quickly reveals which interfaces are up, down, or in an error state. The concept behind this command is to offer a snapshot of the interface health without overwhelming the user with detailed counters or statistics. On Cisco NX-OS (Nexus), the output is formatted as a table with columns for Interface, Status, VRF, Speed, Duplex, and Type. The VRF column is a Nexus-specific addition, reflecting the fact that Nexus switches often operate in a VRF-lite or multi-VRF environment. This command is used in various scenarios: after a reload to verify interfaces come up correctly, during maintenance to confirm administrative shutdowns, or when investigating performance issues to spot speed/duplex mismatches. It fits into troubleshooting workflows as the initial triage step; if an interface shows 'down', further investigation with 'show interface' or 'show logging' is warranted. The command supports filters such as 'status up', 'status down', 'module slot', or 'description' to narrow down results, making it efficient for large switches with hundreds of interfaces. Overall, 'show interface brief' is an indispensable command for daily operations and certification exams alike.
show interface brief [type slot/port | vlan vlan-id | port-channel channel-number | description description | module slot | status {up | down | err-disabled | sfp-absent | not-connected} | unnumbered | summary]When to Use This Command
- Quickly verify the operational status of all interfaces after a reload or configuration change.
- Identify interfaces that are down or in err-disabled state for troubleshooting connectivity issues.
- Check the speed and duplex settings across multiple interfaces to ensure consistency.
- Monitor interface utilization and errors during network performance analysis.
Parameters
| Parameter | Syntax | Description |
|---|---|---|
| type slot/port | ethernet slot/port | mgmt slot/port | Specifies a particular interface by type and number. For example, 'ethernet 1/1' shows only that interface. If omitted, all interfaces are displayed. |
| vlan vlan-id | vlan vlan-id | Filters the output to show only VLAN interfaces (SVIs) with the specified VLAN ID. Useful for checking SVI status. |
| port-channel channel-number | port-channel channel-number | Displays only the specified port-channel interface. Helps in verifying etherchannel status. |
| description description | description description | Filters interfaces by description string. Useful when interfaces have descriptive names for identification. |
| module slot | module slot | Shows interfaces only on a specific module (line card) slot. Useful for modular Nexus chassis. |
| status {up | down | err-disabled | sfp-absent | not-connected} | status {up | down | err-disabled | sfp-absent | not-connected} | Filters interfaces by their operational status. For example, 'status down' shows only interfaces that are down. This is helpful for troubleshooting. |
| unnumbered | unnumbered | Displays interfaces configured as unnumbered (borrow IP from another interface). Rarely used. |
| summary | summary | Provides a summary count of interfaces by status (up, down, admin down, etc.) instead of listing each interface. |
Command Examples
Basic show interface brief
show interface brief-------------------------------------------------------------------------------- Interface Status VRF Speed Duplex Type -------------------------------------------------------------------------------- mgmt0 up -- 1000 full Management Ethernet1/1 up default 1000 full 10/100/1000 Ethernet1/2 down default auto auto 10/100/1000 Ethernet1/3 up default 10000 full 10G-SR Ethernet1/4 admin down default auto auto 10/100/1000 Vlan1 up default -- -- VLAN Vlan10 down default -- -- VLAN Port-channel1 up default -- -- Port-channel --------------------------------------------------------------------------------
The output shows each interface with its status (up/down/admin down), VRF, speed, duplex, and type. mgmt0 is the management interface. Ethernet1/1 is up with 1000/full. Ethernet1/2 is down (likely no cable). Ethernet1/3 is up at 10G. Ethernet1/4 is administratively down. VLAN1 is up, VLAN10 is down. Port-channel1 is up.
Show interface brief with status filter
show interface brief status down-------------------------------------------------------------------------------- Interface Status VRF Speed Duplex Type -------------------------------------------------------------------------------- Ethernet1/2 down default auto auto 10/100/1000 Vlan10 down default -- -- VLAN --------------------------------------------------------------------------------
Filters to show only interfaces that are down. Useful for quickly identifying problem interfaces.
Understanding the Output
The 'show interface brief' command output provides a concise table of all interfaces on the Cisco Nexus switch. The 'Interface' column lists the interface name (e.g., Ethernet1/1, Vlan1, Port-channel1). The 'Status' column indicates the operational state: 'up' means the interface is active and passing traffic; 'down' means the interface is not operational (e.g., no cable, remote end down); 'admin down' means the interface has been manually disabled; 'err-disabled' indicates the interface was disabled due to an error (e.g., loopback, security violation). The 'VRF' column shows the VRF the interface belongs to, typically 'default' or a custom VRF. 'Speed' shows the negotiated or configured speed (e.g., 1000 for 1 Gbps, 10000 for 10 Gbps, 'auto' if not resolved). 'Duplex' shows full or half duplex, or 'auto' if not resolved. 'Type' describes the interface media type (e.g., 10/100/1000 for copper, 10G-SR for fiber, VLAN for SVI, Port-channel for etherchannel). Healthy values are 'up' status with appropriate speed/duplex. Problem values include 'down', 'admin down', 'err-disabled', or mismatched speed/duplex. This command is the first step in interface troubleshooting, allowing rapid identification of non-operational interfaces.
Configuration Scenarios
Verifying Interface Status After Configuration
After configuring a new VLAN interface (SVI) and assigning an IP address, you want to confirm it is up.
Topology
Single Nexus switch with VLAN 100 configured.Steps
- 1.Configure VLAN 100 and SVI interface vlan100 with IP 192.168.100.1/24.
- 2.Use 'show interface brief vlan 100' to verify the SVI status.
! VLAN configuration vlan 100 name Management no shutdown ! SVI configuration interface vlan100 ip address 192.168.100.1/24 no shutdown
Verify: Execute 'show interface brief vlan 100' and confirm the Status is 'up'. If it shows 'down', check that the VLAN is created and the interface is not administratively down.
Watch out: The SVI will remain down until at least one switchport in the VLAN is up and in the same VLAN. Ensure a physical interface is assigned to VLAN 100 and is up.
Identifying Err-Disabled Interfaces
After a network loop, several interfaces may go into err-disabled state. You need to identify them quickly.
Topology
Nexus switch with multiple access ports.Steps
- 1.Use 'show interface brief status err-disabled' to list all err-disabled interfaces.
- 2.Investigate the cause (e.g., loopback, BPDU guard) and re-enable after fixing.
! No configuration needed for this scenario.
Verify: The output will show interfaces with Status 'err-disabled'. Use 'show interface errdisable' for more details.
Watch out: Simply re-enabling an err-disabled interface without fixing the root cause will cause it to go err-disabled again.
Troubleshooting with This Command
The 'show interface brief' command is the first line of defense when troubleshooting connectivity issues on Cisco Nexus switches. When a user reports that a device cannot reach the network, start by running this command to get an overview of all interfaces. Look for interfaces that are 'down' or 'err-disabled'. A 'down' status typically indicates a physical layer issue: the cable is unplugged, the remote device is powered off, or there is a faulty transceiver. An 'err-disabled' status indicates that the interface was automatically disabled due to a detected error, such as a loopback, BPDU guard violation, or UDLD failure. In such cases, check the logs with 'show logging' to see the reason. If an interface is 'admin down', it means an administrator manually shut it down; you can bring it up with 'no shutdown'. For interfaces that are 'up' but experiencing performance issues, the speed and duplex columns can reveal mismatches. For example, if one end is set to 1000/full and the other to auto/auto, the link may negotiate at a lower speed or have duplex mismatch errors. Use 'show interface' to see error counters. The VRF column is important in multi-VRF environments; if an interface is up but traffic doesn't route, ensure the interface is in the correct VRF. For VLAN interfaces (SVIs), the status depends on the underlying VLAN being active and having at least one up switchport. If an SVI is down, check the VLAN status with 'show vlan brief'. The 'show interface brief' command also supports filtering, which is invaluable on large switches. For instance, 'show interface brief status down' quickly isolates problem interfaces. In summary, this command provides a rapid health check of all interfaces, guiding further detailed troubleshooting.
CCNA Exam Tips
Remember that 'show interface brief' does not show error counters; use 'show interface' for detailed stats.
On Nexus, the output includes VRF column, which is not present on classic IOS.
Know that 'admin down' status indicates the interface was shut down manually, while 'down' indicates a physical or protocol issue.
Common Mistakes
Confusing 'down' with 'admin down' – 'down' is operational, 'admin down' is administrative.
Assuming all interfaces are displayed – use 'show interface brief summary' for counts.
Forgetting to check VRF association when troubleshooting routing issues.
Platform Notes
On Cisco NX-OS (Nexus), the 'show interface brief' command includes a VRF column, which is not present in classic Cisco IOS. This reflects the multi-VRF nature of Nexus switches. Additionally, Nexus supports the 'status' filter with options like 'sfp-absent' and 'not-connected', which are not available on IOS. The output format is also slightly different: Nexus uses a table with dashed lines, while IOS uses a more compact format. On IOS, the equivalent command is 'show ip interface brief' for IP status, but 'show interface brief' on IOS does not show VRF. For interface status, IOS uses 'show interfaces status' which includes speed and duplex but not VRF. On Nexus, 'show interface status' is a different command that shows more detailed status including VLAN and port mode. It's important to note that on Nexus, the 'show interface brief' command does not display error counters; use 'show interface' for that. Version differences: On older Nexus releases (e.g., NX-OS 5.x), the command may have fewer filter options. Always check the specific version documentation. For engineers migrating from IOS, remember that the VRF column is a key addition, and the 'status' filter is more granular on Nexus.
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