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Resolution Guide - EX - Verify/Troubleshoot Physical Interface

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Article ID: KB19797 KB Last Updated: 25 Feb 2020Version: 6.0
Summary:

This article explains how to verify that the Physical Interface of an EX switch is UP, and to troubleshoot it if it is not.

To verify an Aggregated Ethernet Interface (LAG) or a VLAN interface, refer to KB22217 - Resolution Guides - EX - Troubleshoot/Verify Interface.

 

Symptoms:

Goals

  • Troubleshoot a Physical Interface that is down.

  • Verify that the Physical Interface is up.

Below is an example of a Physical Interface that is up. The following points are verified and corrected in the step-by-step solution below.

 root@KE-1-4200# run show interfaces ge-0/0/0 terse
 Interface         Admin  Link  Proto       Local Remote  
 ge-0/0/0          up     up                    <<<< Physical Interface 
 ge-0/0/0.0        up     up    eth-switch      <<<< Subinterface (Logical Interface) 
  1. Physical Interface (ge-0/0/0) is Administratively Up and Link Up.

  2. Subinterface (ge-0/0/0.0) is Administratively Up and Link Up.

  3. Correct family is assigned to the Subinterface (ge-0/0/0.0).

 

Solution:

Perform the following steps:

Step 1. Run the following command to view status of the Physical and Subinterface (Logical Interface):

show interfaces <interface> terse

Note: This command output is going to be used throughout this article.

Example:

root@KE-1-4200# run show interfaces ge-0/0/0 terse
Interface      Admin Link Proto Local Remote

ge-0/0/0       up    down            <<<<<<
ge-0/0/0.0     up    down eth-switch

What is the 'Admin' status of the Physical interface (i.e. ge-0/0/0 in the example)?

Step 2.  The interface is Administratively Down, which means the administrator of this switch disabled the interface.

Example:

root@KE-1-4200# run show interfaces ge-0/0/0 terse 
Interface           Admin   Link   Proto    Local       Remote
ge-0/0/0            down    down
ge-0/0/0.0          up      down   eth-switch      

This can be confirmed with the command:

show configuration interfaces <Interface Name> | display set

Example:

root@KE-1-4200# run show configuration interfaces ge-0/0/0 | display set
set interfaces ge-0/0/0 disable
set interfaces ge-0/0/0 unit 0 family ethernet-switching

Bring the interface Administratively Up by enabling the interface with the command:

delete interfaces <Interface Name> disable

Example:

root@KE-1-4200# delete interfaces ge-0/0/0 disable 

Important NoteWe strongly recommend that you check with the network administrator before issuing this command, as it will alter the network topology.

For more information on disabling Physical Interfaces, refer to Disabling a Physical Interface.

Continue with Step 3 (when the interface is Administratively Up).

Step 3.  What is the 'Link' status of the Physical interface (i.e. ge-0/0/0)?

Example

root@KE-1-4200# run show interfaces ge-0/0/0 terse
Interface      Admin Link   Proto    Local Remote

ge-0/0/0       up    down          <<<<<
ge-0/0/0.0     up    down   eth-switch
  • Up - Jump to Step 9 and perform the Subinterface (Logical interface) check

  • Down - Continue to Step 4  

Step 4.  Display the interface speed and duplex settings with the command:

run show configuration interfaces ge-0/0/0 | display set

(The default is 'auto' in Junos.)

Example:

root@KE-1-4200# run show configuration interfaces ge-0/0/0 | display set
set interfaces ge-0/0/0 ether-options no-auto-negotiation
set interfaces ge-0/0/0 ether-options link-mode full-duplex
set interfaces ge-0/0/0 ether-options speed 1g
set interfaces ge-0/0/0 unit 0 family ethernet-switching
Are the speed and duplex settings still set to 'auto'?
  • Yes - Continue to Step 5

  • No - If Speed/Duplex been configured make sure the configuration of the EX port matches the Far-end/peer port settings.  If not resolved, continue to Step 5.  

Step 5.  Confirm the cable is connected to the port. 

  • If you have physical access to the EX switch, verify the cable is connected to the affected interface.  Make sure the link light is on for that interface to confirm the cable is firmly seated.  (Try unplugging & re-plugging if possible.)

  • If you do not have physical access, use JWeb to identify the interface connectivity. The port will be green if the Physical Link is detected.

Step 6.  If another working port is available, does the same cable work in another working port?

  • Yes - Suspect bad port.  Contact your technical support representative.

  • No - Continue to Step 7  

Step 7.  Does the link come up with another working (known good) cable?

  • Suspect cable could have gone bad.

  • Try with different cable.

  • Perform Cable Test to make sure it's not a cable issue:

  • Yes - Replacing the cable fixed the issue.  Physical interface is up.  Jump to Step 9 to perform the Subinterface (Logical interface) check.

  • No - Continue to Step 8.

Step 8.  View the logs for errors with the command:

show log messages | match <Interface Name>

If the reason for the Physical link down cannot be resolved, contact your technical support representative.

Step 9.  [Subinterface Check]  Continuing to look at the output of 'show interfaces <int> terse', the Subinterface (i.e. ge-0/0/0.0) has to be checked.

Now observe the Subinterface line output (i.e. ge-0/0/0.0 in the example):

Example:

root@KE-1-4200# run show interfaces ge-0/0/0 terse
Interface      Admin Link  Proto Local Remote

ge-0/0/0       up    down
ge-0/0/0.0     up    down  eth-switch    <<<<<<<  Subinterface (Logical Interface)

Is the Subinterface/ Unit mapped to the correct Protocol family ? (Layer 2 = 'eth-switch' and  Layer 3 = 'Inet' )

  • Yes - Continue to Step 10

  • No - Configuration issue. For more information on Protocol Family, refer to family (for EX Series switches).

  • Logical Interface is not listed  (ge-0/0/0.0)

root@KE-1-4200# run show interfaces ge-0/0/0 terse     Interface   Admin  Link  Proto  Local  Remote  
ge-0/0/0    up     up      

Which means Logical/Subinterface (unit 0) for this Physical Interface(ge-0/0/0) is not defined.

Verification:

root@KE-1-4200# run show configuration interfaces ge-0/0/0 | display set 

Nothing Configured under Interface ge-0/0/0 Hierarchy

Solution:

root@KE-1-4200# set interfaces ge-0/0/0 unit 0 family ethernet-switching

Step 10.  What is the 'Admin' status of the Subinterface (Logical Interface)?

Example:

root@KE-1-4200# run show interfaces ge-0/0/0 terse
Interface     Admin Link  Proto Local Remote
ge-0/0/0      up    down
ge-0/0/0.0    up    up    eth-switch     <<<<
  • Down - Enable the logical interface with the command as discussed in Step 2.

  • Up - End of workflow - Your Physical Interface has been verified as Up.  For example:

    root@KE-1-4200# run show interfaces ge-0/0/0 terse
    Interface    Admin  Link  Proto       Local Remote
    ge-0/0/0      up     up                     <<<< Physical Interface 
    ge-0/0/0.0    up     up    eth-switch      <<<< Subinterface (Logical Interface)  
    1. Physical Interface (ge-0/0/0) is Administratively Up and Link Up.

    2. Subinterface (ge-0/0/0.0) is Administratively Up and Link Up.

    3. Correct family is assigned to the Subinterface (ge-0/0/0.0).

Technical Documentation

Network Interfaces for EX Series Switches

 

Modification History:

2020-02-25: Article reviewed for accuracy; links updated

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