show interface loopback

To display information about the loopback interface, use the show interface loopback command.

show interface loopback lo-number [ brief | description ]

Syntax Description

lo-number
Loopback interface number. The range is from 0 to 1023.
brief
(Optional) Displays a brief summary of the loopback interface information.
description
(Optional) Displays the description provided for the loopback interface.

Command Default

None

Command Modes

EXEC mode

Command History

Release
Modification
5.0(3)N1(1)
This command was introduced.

Examples

This example shows how to display the configuration information for a specific loopback interface:

switch# show interface loopback 10
loopback10 is up
Hardware: Loopback
MTU 1500 bytes, BW 8000000 Kbit, DLY 5000 usec,
reliability 255/255, txload 1/255, rxload 1/255
Encapsulation LOOPBACK
0 packets input 0 bytes
0 multicast frames 0 compressed
0 input errors 0 frame 0 overrun 0 fifo
0 packets output 0 bytes 0 underruns
0 output errors 0 collisions 0 fifo
 
switch#
 

The table below describes the significant fields shown in the display.

show interface loopback Field Description
Field
Description
Loopback is ...
Indicates whether the interface hardware is currently active (whether carrier detect is present), is currently inactive (down), or has been taken down by an administrator (administratively down).
Hardware
Hardware is Loopback.
MTU
Maximum transmission unit (MTU) of the interface.
BW
Bandwidth (BW) of the interface in kilobits per second.
DLY
Delay (DLY) of the interface in microseconds.
reliability
Reliability of the interface as a fraction of 255 (255/255 is 100 percent reliability), calculated as an exponential average over 5 minutes.
txload
Load on the interface for transmitting packets as a fraction of 255 (255/255 is completely saturated), calculated as an exponential average over 5 minutes.
rxload
Load on the interface for receiving packets as a fraction of 255 (255/255 is completely saturated), calculated as an exponential average over 5 minutes.
Encapsulation
Encapsulation method assigned to interface.
LOOPBACK
Indicates whether loopback is set.
packets input
Total number of error-free packets received by the system.
bytes
Total number of bytes, including data and MAC encapsulation, in the error-free packets received by the system.
multicast frames
Total number of multicast frames enabled on the interface.
compressed
Total number of multicast frames compressed on the interface.
input errors
Sum of all errors that prevented the receipt of datagrams on the interface being examined. This may not balance with the sum of the enumerated output errors, because some datagrams may have more than one error and others may have errors that do not fall into any of the specifically tabulated categories.
frame
Number of packets received incorrectly having a CRC error and a noninteger number of octets. On a serial line, this is usually the result of noise or other transmission problems.
overrun
Number of times the serial receiver hardware was unable to hand received data to a hardware buffer because the input rate exceeded the receiver’s ability to handle the data.
fifo
Number of First In, First Out (FIFO) errors in the receive direction.
packets output
Total number of messages transmitted by the system.
bytes
Total number of bytes, including data and MAC encapsulation, transmitted by the system.
underruns
Number of times that the far-end transmitter has been running faster than the near-end router's receiver can handle. This may never happen (be reported) on some interfaces.
output errors
Sum of all errors that prevented the final transmission of datagrams out of the interface being examined. Note that this may not balance with the sum of the enumerated output errors, as some datagrams may have more than one error, and others may have errors that do not fall into any of the specifically tabulated categories.
collisions
Loopback interface does not have collisions.
fifo
Number of First In, First Out (FIFO) errors in the transmit direction.

This example shows how to display the brief information for a specific loopback interface:

switch# show interface loopback 10 brief
 
--------------------------------------------------------------------------------
Interface Status Description
--------------------------------------------------------------------------------
loopback10 up --
switch#
 

Related Commands

Command
Description
interface loopback
Configures a loopback interface.