Specifications

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Cisco MGX 8850 (PXM45) and MGX 8950 Software Configuration Guide
Release 3, Part Number 78-14788-01 Rev. C0, January 2004
Chapter 7 Switch Operating Procedures
Configuring a line loopback
Enter the dsplns <line type> <bay.line> command to verify that the appropriate line is in the specified
loopback state. Replace <line type> with the appropriate line type. Replace <bay.line> with the
appropriate bay and line number.
M8850_NY.1.AXSM.a > dspln -sonet 1.1
Line Number : 1.1
Admin Status : Up Alarm Status : Clear
Loopback : Local APS enabled : Disable
Frame Scrambling : Enable Number of ports : 0
Xmt Clock source : localTiming Number of partitions: 0
Line Type : sonetSts12c Number of SPVC : 0
Medium Type(SONET/SDH) : SONET Number of SPVP : 0
Medium Time Elapsed : 654 Number of SVC : 0
Medium Valid Intervals : 0
Medium Line Type : ShortSMF
In the following example, the user adds a local loop on an AXSM card’s sonet line.
M8850_NY.1.AXSM.a > addlnloop -sonet 1.1 -lpb 2
Line loop-back status will be changed.
Do you want to proceed (Yes/No) ? y
Note Before you can change the loopback type for an existing loopback, you must firs‘t delete the loopback
by executing dellnloop, or you can just enter the addlnloop command with the -lpb 1 (No loopback)
option.
Deleting a Loopack State
Enter the dellnloop <line type> <bay.line> command to delete a loopback state on a specified line.
Replace <line type> with the appropriate line type. Replace <bay.line> with the appropriate bay and line
number.
M8850_NY.1.AXSM.a > dellnloop -sonet 1.1
Enter the dsplns command to verify that the loopback state was deleted on the appropriate line.
Configuring a line loopback
If a connection fails and you do not know which end of the connection is causing the problem, putting a
line into loopback mode can help you determine what the problem is and where it occurs on a connection.
In an MGX 8850 and MGX 8950 switches, loopback lines provide CLI-based line level monitoring
capabilities.
When a line is put into loopback, the receiving switch takes all of the data it receives and returns it
unchanged back to the sender. The physical line in a loopback configuration is connected between a CPE
and a switch; one physical line is connected from the tx (Transmit port) of the CPE to the rx (receive)
port of a card on the switch you are testing. Another physical line is connected between the tx port of
the same card and the receive port of the CPE.