Looping a circuit

===READ THIS FIRST===

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*<b><font color="red">WARNING:</font></b> Looping a circuit from remote equipment will cause connection to be lost unless an alternate means of connection is available. If connection is lost and there is no alternate means of connecting, you will be unable to remove the loop without physical access to the device.

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*<b><font color="blue">CAUTION:</font></b> Looping a circuit will cause loss of connectivity for that connection. Ensure that intrusive testing is authorized and the connection is not in use.

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===Initial Steps===

Looping a circuit is a test in and of itself, as well as a tool to enable and enhance other testing methods. The following commands will describe how to perform a remote loop to the [[Smartjack | smartjack]]. Typically you will only loop from core equipment to the remote site.

#Telnet in to core router.

#Enter enable/exec mode.

#Perform a [[Show Interfaces Command | <code>show interface serial</code>]] to verify the status of the interface you wish to loop.

#*If a loop already exists on the interface, you will be unable to loop it again. You will need to clear the loop before continuing.

#*If you are unable to clear the loop, it is likely that the carrier has placed a loop on the circuit within their equipment. You will need to engage them to clear the loop before continuing.

#Make note of the hardware type, as this will determine the type of commands required.

===Loop the Circuit===

#Choose the applicable device and hardware type below and follow steps 1 through 3.

#Exit configuration/test mode (Ctrl-Z)

#Run a <code>show interface</code> command to verify that the loop has taken effect.

#For further troubleshooting steps to take while the circuit is looped, follow instructions in the Follow Up section.

====Cisco====

The most common core equipment you will be dealing with will be Cisco based. Core routers have several different types of controllers that may be used, each requiring a slightly different command set to loop the circuit.

=====SPA-4XT3/E3=====

#Enter configuration mode:

#*<code>Router#conf t</code>

#Designate the applicable controller:

#*<code>Router(config)#int se [t3/s/p]</code>

#To loop the circuit, enter the following command:

#*<code>Router(config-if)#loopback remote</code>

#To remove the loop, enter the following command:

#*<code>Router(config-if)#no loopback remote</code>

=====SPA-2XCT3/DS0=====

#Enter configuration mode:

#*<code>Router#conf t</code>

#Designate the applicable controller:

#*<code>Router(config)#controller t3 [t3/s/p]</code>

#To loop the circuit, enter the following command:

#*<code>Router(config-controller)#t1 [t1] loopback remote line fdl bellcore</code>

#To remove the loop, enter the following command:

#*<code>Router(config-controller)#no t1 [t1] loopback remote</code>

=====Multichannel T1=====

#Enter configuration mode:

#*<code>Router#conf t</code>

#Designate the applicable controller:

#*<code>Router(config)#controller t1 [t1/p]</code>

#To loop the circuit, enter the following command:

#*<code>Router(config-controller)#loopback remote iboc</code>

#To remove the loop, enter the following command:

#*<code>Router(config-controller)#no loopback remote iboc</code

</code>

====Adtran====

#Enter configuration mode:

#*<code>Router#conf t</code>

#Designate the applicable interface:

#*<code>Router(config)#int t1 [x]</code>

#To loop the circuit, enter the following command:

#*<code>Router(config-t1 [x])#loopback remote line fdl</code>

#To remove the loop, enter the following command:

#*<code>Router(config-t1 [x])#no loopback remote</code>

====Samsung====

*'''NOTE:''' Samsung AOS only supports ANSI FDL remote loops to the CSU.

#Enter test mode:

#*<code>Router#test</code>

#Set the applicable T1 controller:

#*<code>Router/test#t1 p/s</code>

#To loop the circuit, enter the following command:

#*<code>Router/test/t1 (p/s)#loopback remote line ansi_fdl</code>

#To remove the loop, enter the following command:

#*<code>Router/test/t1 (p/s)#no loopback</code>

====Juniper====

''No information available at this time.''

===Follow Up===

====Additional Testing====

There are several follow up troubleshooting steps that can be taken while the circuit is still looped. See ''[[Bit Error Rate Testing]]'' and ''[[Extended Ping Testing]]''.

The state of the interface once a loop has been applied can be used as an additional indicator for troubleshooting.

====Circuit Will Not Loop====

====Circuit Looped (Down/Down)====

====Circuit Looped (Up/Down)====

====Circuit Looped (Down/Up)====

====Circuit Looped (Up/Up)====

===Reference Material===

[[Category:How-To]][[Category:Troubleshooting]]