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This section includes the following information to assist you when troubleshooting T3 interfaces:

To use loopback testing to isolate T3 interface problems.

Table 1 provides links and commands for using loopback testing for T3 interfaces.

Table 1: Checklist for Using Loopback Testing for T3 Interfaces

Diagnose a Suspected Hardware Problem with a T3 Interface	Command or Action

Create a Loopback
Create a Physical Loopback	Connect the transmit port to the receive port.
Configure a Local Loopback	[edit interfaces interface-name t3-options] set loopback local show commit
Set Clocking to Internal	[edit interfaces interface-name] set clocking internal show commit
Verify That the T3 Interface Is Up	show interfaces t3-fpc/pic/port
Clear T3 Interface Statistics	clear interfaces statistics t3-fpc/pic/port
Force the Link Layer To Stay Up
Configure Encapsulation to Cisco-HDLC	[edit interfaces interface-name] set encapsulation cisco-hdlc show commit
Configure No-Keepalives	[edit interfaces interface-name] set no-keepalives show commit
Verify the Status of the Logical Interface	show interfaces t3-fpc/pic/port show interfaces t3-fpc/pic/port terse
Ping the T3 Interface	ping interface t3-fpc/pic/port local-IP-address bypass-routing count 1000 rapid
Check for T3 Interface Error Statistics	show interfaces t3-fpc/pic/port extensive
Diagnose a Suspected Circuit Problem
Create a Loop from the Router to the Network	[edit interfaces interface-name t3-options] set loopback remote show commit
Create a Loop to the Router from Various Points in the Network	Perform Steps 2 through 8 from Diagnose a Suspected Hardware Problem with a T3 Interface.