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Resolution Guide - EX - Troubleshoot VLAN interface

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Article ID: KB22220 KB Last Updated: 20 May 2020Version: 6.0
Summary:

This article details steps to verify whether a VLAN interface is up, and to troubleshoot a VLAN interface that is down.

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

 

Symptoms:

Symptoms:

  • Troubleshoot a VLAN Interface that is down.

  • VLAN interface is not coming up.

 

Solution:

Perform the following steps:

  1. Run the following command to display the 'Admin' status of the VLAN interface:

show interfaces <vlan interface> terse

Example:

root@ex> run show interfaces vlan.10 terse
Interface   Admin   Link  Proto   Local      Remote
vlan.10     up      up    inet    10.0.0.1/24 

What is the 'Admin' status of the VLAN interface?

  • Up - This means that the VLAN Layer-3 Sub-Interface is Administratively Enabled. Continue to Step 3.

  • Down - If the Admin status of the VLAN Interface is Down, then Continue to Step 2.

  1. The interface is Administratively Down, which means that the administrator of this switch disabled the interface.

root@KE-1-4200# run show interfaces vlan.30 terse
Interface  Admin   Link  Proto  Local      Remote
vlan.30   down    down  inet   30.0.0.1/24 

This can be confirmed with the following command:

show configuration interfaces <vlan interface> | display set

Example:

root@KE-1-4200# run show configuration interfaces vlan.30 | display set
set interfaces vlan unit 30 disable
set interfaces vlan unit 30 family inet address 30.0.0.1/24

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

delete interfaces vlan unit <vlan id> disable

Example:

root@KE-1-4200# delete interfaces vlan unit 30 disable

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

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

  1. What is the 'Link' status of the VLAN interface?

root@ex> run show interfaces vlan.10 terse
Interface  Admin    Link  Proto   Local      Remote
vlan.10    up      up    inet    10.0.0.1/24 
  1. Run the following command to verify that the physical interfaces are correctly mapped to the VLAN:

run show  vlans <Vlan Name> 

Example:

root@KE-1-4200# run show vlans DATA-1
Name           Tag     Interfaces
DATA-1         10     
                       ae0.0, ge-0/0/0.0*, ge-0/0/3.0, ge-0/0/10.0

Are all the physical interfaces listed?

  • Yes - Continue to Step 5.

  • No - Add the physical interfaces as shown in the above example:  set vlans <VLAN Name> interface <Interface name>

root@KE-1-4200# set vlans TEST interface ge-0/0/0 

For more information on Layer 3 Subinterfaces, refer to Example: Configuring Layer 3 Subinterfaces for a Distribution Switch and an Access Switch.

  1. Verify that the interfaces are active with the following command:

show vlans <vlan>

Example:

root@KE-1-4200# run show vlans TEST
Name Tag Interfaces
TEST 30
ge-0/0/0.0*, ge-0/0/1.0

Asterisk “ * “ denotes the active connection for the interface/Switch Port.

In the above example, interface ge-0/0/0 has a client detected, but ge-0/0/1 does not.

Is there an ( * ) on at least one physical interface of that VLAN?

  • Yes: End of Workflow. Your VLAN is up. See other helpful commands and links.

    Note: If an ( * ) is found next to the physical interface, but that VLAN interface is still down, then contact your technical support representative.

  • No: In order to make a VLAN Interface active, at least one physical interface has to be up on the VLAN. An expected Physical Interface has a physical connection, but it is not detected.  

To fix this, proceed with the following Resolution Guide for all the Physical Interfaces that do NOT have an ( * ): KB19797 - Resolution Guide - EX - Troubleshoot Physical Interface

Then your VLAN should become up.

Other Helpful Commands 

show ethernet-switching interfaces

 

Modification History:

2020-05-20: ​Article reviewed for accuracy, no changes required; article accurate and valid

 

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