InterfacesEXEC

show interfaces

Displays detailed status and statistics for all interfaces or a specific interface on Cisco IOS-XR.

Overview

The 'show interfaces' command is one of the most fundamental and frequently used commands in Cisco IOS-XR. It provides a comprehensive view of the operational status, configuration, and performance statistics for all interfaces on the router. This command is essential for network engineers to verify interface connectivity, diagnose physical and data link layer issues, monitor bandwidth utilization, and troubleshoot performance problems.

In Cisco IOS-XR, the command syntax is similar to classic IOS but with some differences in interface naming (type interface-path-id format, e.g., GigabitEthernet0/0/0/0). The output includes detailed counters for packets, bytes, errors, and drops, as well as interface characteristics like MTU, bandwidth, duplex, and speed. The command can be used in EXEC mode and supports various modifiers like 'brief' for a summary table, 'description' to show only descriptions, 'accounting' for per-protocol statistics, and 'rates' for current bit rates.

When to use: whenever you need to check if an interface is up, verify its IP address, monitor traffic load, or investigate packet loss. It is the first step in troubleshooting connectivity issues. For example, if a remote site is unreachable, 'show interfaces' on the connecting interface can quickly reveal if the link is down or has excessive errors. The command also helps in capacity planning by showing average utilization over 5 minutes. In IOS-XR, the output is consistent across platforms, making it a reliable tool for network operations.

Syntax·EXEC

show interfaces [type interface-path-id] [brief | description | accounting | rates | detail]

When to Use This Command

Verify interface operational status (up/down) and line protocol state.
Check interface error counters (CRC, runts, giants, input/output errors) to diagnose physical layer issues.
Monitor interface bandwidth utilization and packet rates for capacity planning.
Inspect interface MTU, MAC address, and encapsulation settings for configuration verification.

Parameters

Parameter	Syntax	Required	Description
type interface-path-id	GigabitEthernet0/0/0/0	Optional	Specifies a particular interface. If omitted, all interfaces are shown. The format is type (e.g., GigabitEthernet, TenGigE, Loopback) followed by rack/slot/module/port.
brief	brief	Optional	Displays a one-line summary per interface showing status and protocol. Useful for quick overview.
description	description	Optional	Shows only the interface description string. Useful for documentation checks.
accounting	accounting	Optional	Displays per-protocol packet and byte counts. Useful for understanding traffic composition.
rates	rates	Optional	Shows current input and output bit rates and packet rates. Useful for real-time monitoring.
detail	detail	Optional	Provides additional details such as interface statistics per VLAN or per subinterface. Not commonly used.

Command Examples

Basic interface status check

show interfaces GigabitEthernet0/0/0/0

GigabitEthernet0/0/0/0 is up, line protocol is up 
  Interface state transitions: 1
  Hardware is GigabitEthernet, address is 00ab.cdef.1234 (bia 00ab.cdef.1234)
  Internet address is 10.1.1.1/24
  MTU 1514 bytes, BW 1000000 Kbit
     reliability 255/255, txload 1/255, rxload 1/255
  Encapsulation ARPA,
  Full-duplex, 1000Mb/s, link type is autonegotiation
  output flow control is ON, input flow control is ON
  Loopback not set
  Last input 00:00:00, output 00:00:00
  Last clearing of "show interface" counters never
  5 minute input rate 1000 bits/sec, 2 packets/sec
  5 minute output rate 500 bits/sec, 1 packets/sec
     12345 packets input, 1234567 bytes, 0 total input drops
     Received 0 broadcast, 0 multicast
     0 runts, 0 giants, 0 throttles, 0 parity
     0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored
     12345 packets output, 1234567 bytes, 0 total output drops
     0 output errors, 0 underruns, 0 applique, 0 resets
     0 output buffer failures, 0 output buffers swapped out
     0 carrier transitions

The first line shows interface and line protocol status. 'up/up' indicates operational. Next lines show hardware address, IP, MTU, bandwidth, reliability, load, duplex, speed, flow control, loopback, last input/output, clearing counters, 5-minute average rates, and detailed packet/byte counts with error statistics.

Brief summary of all interfaces

show interfaces brief

Interface                      Status         Protocol         Description
Gi0/0/0/0                      up             up               
Gi0/0/0/1                      up             up               
Gi0/0/0/2                      admin-down     down             
Gi0/0/0/3                      up             down             
Loopback0                      up             up               
MgmtEth0/0/CPU0/0              up             up               Management

Provides a concise table of all interfaces with status (up/down/admin-down) and protocol state. Useful for quick overview.

Understanding the Output

The 'show interfaces' output on IOS-XR provides a wealth of information. The first line indicates the interface administrative status (up/down) and line protocol status (up/down). 'up/up' means the interface is operational. 'up/down' indicates a Layer 1 issue (e.g., cable) or Layer 2 problem (e.g., keepalive). 'admin-down/down' means the interface was manually shut down. The 'Interface state transitions' counter shows how many times the interface has changed state, useful for detecting flapping. Key fields include: 'MTU' (maximum transmission unit), 'BW' (bandwidth in Kbps), 'reliability' (255/255 is perfect, lower indicates errors), 'txload/rxload' (load as fraction of 255, high values indicate congestion). 'Encapsulation' shows Layer 2 type (e.g., ARPA for Ethernet). Duplex and speed are critical for performance; mismatches cause errors. 'Last input/output' timestamps show recent activity; if 'never' appears, the interface may be idle or stuck. Error counters: 'runts' (frames smaller than minimum), 'giants' (frames exceeding maximum), 'CRC' (cyclic redundancy check errors indicating corruption), 'input errors' (total receive errors), 'output errors' (total transmit errors). High error counts suggest physical layer issues (bad cable, faulty transceiver, duplex mismatch). 'Total input drops' and 'total output drops' indicate packet loss due to congestion or hardware limitations. The '5 minute input/output rate' gives average bandwidth utilization; sustained high load may require link upgrade.

Configuration Scenarios

Verifying a newly configured interface

After configuring GigabitEthernet0/0/0/0 with an IP address, verify it is operational.

Topology

[Router] --- Gi0/0/0/0 --- [Switch]

Steps

1.Configure interface with IP address and no shutdown.
2.Use 'show interfaces GigabitEthernet0/0/0/0' to verify status.

Configuration

!
interface GigabitEthernet0/0/0/0
 ipv4 address 10.1.1.1 255.255.255.0
 no shutdown
!

Verify: Check that first line shows 'up, line protocol is up'. Verify IP address is correct. Ensure no error counters are incrementing rapidly.

Watch out: If the interface shows 'up, line protocol is down', check Layer 1 (cable, transceiver) or Layer 2 (e.g., CDP/LLDP mismatch).

Troubleshooting high error rates

Users report slow connectivity; suspect interface errors.

Topology

[Router] --- Gi0/0/0/1 --- [ISP]

Steps

1.Run 'show interfaces GigabitEthernet0/0/0/1'.
2.Examine CRC, runts, giants, input errors counters.

Configuration

N/A

Verify: If CRC errors are high and increasing, suspect faulty cable or transceiver. If runts are high, check for collisions or duplex mismatch. If output drops are high, check for congestion.

Watch out: A few CRC errors at link-up are normal; focus on sustained increments. Duplex mismatch often causes both CRC and runts.

Troubleshooting with This Command

When troubleshooting network issues on Cisco IOS-XR, 'show interfaces' is your first diagnostic tool. Start by checking the interface status: if the line protocol is down, the issue is likely physical (cable, transceiver, or far-end device). If the interface is up but the protocol is down, investigate Layer 2 issues (e.g., keepalive, encapsulation mismatch). Use the 'brief' option to quickly scan all interfaces for anomalies.

Examine error counters: 'input errors' and 'output errors' are aggregate counters. High 'CRC' errors indicate data corruption, often due to bad cabling, faulty SFP, or electromagnetic interference. 'Runts' and 'giants' suggest collisions or MTU mismatches. 'Input drops' and 'output drops' indicate packet loss; output drops typically mean the interface is congested (check 'txload'). 'Overrun' and 'underrun' errors point to hardware buffer issues.

Monitor the 5-minute average rates: if 'rxload' or 'txload' consistently exceed 50% (128/255), consider upgrading the link. The 'reliability' field (255/255 is perfect) drops when errors are frequent. Also check 'Last input' and 'Last output'; if they show 'never', the interface may be stuck or not receiving/sending traffic. Use 'clear counters' to reset statistics before further troubleshooting. For persistent issues, inspect the physical layer: swap cables, SFPs, or ports. The command 'show interfaces accounting' can reveal which protocols are consuming bandwidth.

CCNA Exam Tips

Memorize the first line: 'is up, line protocol is up' indicates a fully operational interface.

Know that 'input errors' and 'CRC' are key indicators of Layer 1 problems; high values suggest faulty cabling or hardware.

Understand that 'output drops' often indicate congestion; check 'txload' to confirm.

Common Mistakes

Confusing administrative status (up/down) with line protocol status; both must be 'up' for operation.

Ignoring error counters; a few errors are normal, but sustained high counts indicate a problem.

Assuming 'show interfaces' shows only physical interfaces; it also shows subinterfaces, loopbacks, and management interfaces.

Platform Notes

In Cisco IOS-XR, the 'show interfaces' command behaves similarly to classic IOS but with key differences. Interface naming uses the 'type interface-path-id' format (e.g., TenGigE0/0/0/0) instead of the classic 'type slot/port' (e.g., GigabitEthernet0/1). The output includes fields like 'output flow control' and 'input flow control' which are not always present in IOS. The 'reliability' field is a fraction out of 255, same as IOS. The '5 minute input/output rate' is calculated differently; IOS-XR uses an exponential decay algorithm.

On IOS-XR, the command supports additional keywords like 'rates' and 'accounting' that provide more granular data. The 'brief' output includes a 'Description' column by default, unlike IOS where you need 'show interfaces description'. For management interfaces, use 'MgmtEth0/0/CPU0/0'. Loopback interfaces are displayed as 'Loopback0'. Subinterfaces are shown with a dot notation (e.g., GigabitEthernet0/0/0/0.100).

Equivalent commands on other platforms: On Juniper JunOS, use 'show interfaces terse' for brief or 'show interfaces extensive' for detailed stats. On Arista EOS, 'show interfaces' is similar but uses different naming. On Cisco IOS (classic), the command is identical but interface naming differs. Version differences: In IOS-XR 6.0+, the output includes 'total input drops' and 'total output drops' as separate counters. Always refer to the specific IOS-XR version documentation for exact field meanings.

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