
•
Local—Useful for troubleshooting physical PIC errors. Configuring local loopback on
an interface allows transmission of packets to the channel service unit (CSU) and then
to the circuit toward the far-end device. The interface receives its own transmission,
which includes data and timing information, on the local router's PIC. The data received
from the CSU is ignored. To test a local loopback, issue the show interfaces
interface-name command. If PPP keepalives transmitted on the interface are received
by the PIC, the Device Flags field contains the output Loop-Detected.
•
Payload—Useful for troubleshooting the physical circuit problems between the local
router and the remote router. A payload loopback loops data only (without clocking
information) on the remote router’s PIC. With payload loopback, overhead is
recalculated.
•
Remote—Useful for troubleshooting the physical circuit problems between the local
router and the remote router. A remote loopback loops packets, including both data
and timing information, back on the remote router’s interface card. A router at one end
of the circuit initiates a remote loopback toward its remote partner. When you configure
a remote loopback, the packets received from the physical circuit and CSU are received
by the interface. Those packets are then retransmitted by the PIC back toward the
CSU and the circuit. This loopback tests all the intermediate transmission segments.
Table 7 on page 106 shows the loopback modes supported on the various interface types.
Table 7: Loopback Modes by Interface Type
Usage GuidelinesLoopback ModesInterface
Configuring Ethernet Loopback CapabilityLocalAggregated Ethernet,
Fast Ethernet, Gigabit
Ethernet
Configuring E1 Loopback CapabilityLocal and remoteCircuit Emulation E1
Configuring T1 Loopback CapabilityLocal and remoteCircuit Emulation T1
Configuring E1 Loopback Capability and
Configuring E3 Loopback Capability
Local and remoteE1 and E3
“Configuring NxDS0 IQ and IQE Interfaces” on
page 8, Configuring T1 and NxDS0 Interfaces,
Configuring Channelized OC12/STM4 IQ and IQE
Interfaces (SONET Mode), Configuring
Channelized STM1 IQ and IQE Interfaces, and
Configuring Channelized T3 IQ Interfaces
PayloadNxDS0
Configuring Serial Loopback CapabilityLocal and remoteSerial (V.35 and X.21)
Configuring Serial Loopback CapabilityDCE local, DCE
remote, local, and
remote
Serial (EIA-530)
Configuring SONET/SDH Loopback CapabilityLocal and remoteSONET/SDH
Copyright © 2014, Juniper Networks, Inc.106
Channelized E1 Interfaces Feature Guide for Routing Devices
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