Command Reference Guide

3Com Router 3000 Ethernet Family
Command Reference Guide Chapter 1 Interface Management Commands
3Com Corporation
1-12
Description
Use the looptest command to test whether an interface or line is in a loop.
Loop test is available only on synchronous serial interfaces (including those formed on
E1/T1/E1-F/T1-F interfaces) using SD701 chips.
A loop test on an interface starts by sending a test packet. If the interface is in a local or
line loop, the test packet just sent will loop back to the interface.
In addition to testing interface or line loops, you may use this command to test the
transmission quality of a loopback line.
The output of this command provides information about:
z Receiving state of test packets. If a test packet does not loop back to the sending
interface upon timeout, the message “Wait time out” is displayed. If it does loop
back, information about number of bytes, sequence number, and delay is
displayed for the packet.
z Final statistics about sent test packets, received test packets, lost packets,
received error packets, percentage of lost packets, percentage of error packets,
delay in its minimum/average/maximum, and test conclusion.
For a line with a low transmission speed, increase the timeout waiting for receiving a
sent test packet.
Related command: loopback, fe1 loopback, ft1 loopback.
Example
# Test whether interface Serial 1/0/0 and its connected line is in a loop.
<3Com > looptest interface serial 1/0/0
LOOPTEST Serial1/0/0: 52 data bytes, press CTRL_C to break
Receive from Serial1/0/0: bytes=52 sequence=1 time=1 ms
Receive from Serial1/0/0: bytes=52 sequence=2 time=1 ms
Receive from Serial1/0/0: bytes=52 sequence=3 time=1 ms
Receive from Serial1/0/0: bytes=52 sequence=4 time=1 ms
Receive from Serial1/0/0: bytes=52 sequence=5 time=1 ms
--- Serial1/0/0 looptest statistics ---
5 packet(s) transmitted
5 packet(s) received
0 packet(s) lost
0 packet(s) error
0.00% packet lost
0.00% packet error
round-trip min/avg/max = 1/1/1 ms
conclusion: loopback