Verify LAG (Link Aggregation Group) of a Juniper Networks EX Series switch is UP and troubleshoot it if it is not.

To verify a Physical Interface (non-aggregated) or a VLAN interface, refer to KB22217 - Resolution Guides - EX - Troubleshoot/Verify Interface [juniper.net].

Goals:

• Troubleshoot down Aggregated Ethernet Interface (LAG).
• Verify Aggregated Ethernet Interface (LAG) is up.
• Below is an example of a LAG that is up.  This is what be verified and corrected in the step-by-step solution below.

  root@KE-1-4200# run show interfaces terse | match ae0     
  ge-0/0/5.0       up    up   aenet    --> ae0.0   <<<<< LAG Child Interface
  ge-0/0/6.0       up    up   aenet    --> ae0.0   <<<<< LAG Child Interface
  ae0              up    up                  <<<<< LAG Parent Interface
  ae0.0            up    up   eth-switch     <<<<< LAG Logical Interface

1. LAG parent interface (ae0) and LAG logical interface (ae0.0) are Administratively Up
2. LAG parent interface (ae0) and LAG logical interface (ae0.0) are Link Up
3. Child interfaces (ge-0/0/5.0 and ge-0/0/6.0) are Administratively Up
4. Child interfaces (ge-0/0/5.0 and ge-0/0/6.0) are Link Up
5. Correct family is assigned to the LAG logical (ae0.0) interface

Perform the following steps:

Run the following command to view the status of the Aggregated Ethernet Interface:

root@switch> show interfaces <ae interface> terse

Example:

root@switch> show interfaces ae0 terse 
Interface         Admin     Link        Proto    Local    Remote
ae0               up         down   
ae0.0             up        down        eth-switch 
 

What is the 'Admin' status of the ae interface (i.e. ae0 in the example)?

• Up - Jump to Step 3
• Down - Continue to Step 2
• Interface is not listed -
  
  root@switch> show interfaces ae0 terse
error: device ae0 not found
  
  
  If the expected Aggregated Ethernet Interface is not listed, then it could be a configuration issue. Refer to the technical documentation on Configuring Aggregated Ethernet Interfaces (CLI Procedure) .
  Make sure the aggregated-devices ethernet device-count is specified.

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

This can be confirmed with the command:

show configuration interfaces <aeX interface> | display set
Example:

root@switch# show interfaces ae0 | display set 
set interfaces ae0 disable
set interfaces ae0 unit 0 family ethernet-switching  

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

delete interfaces <ae interface> disable

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

Example:
root@switch# delete interfaces ae0 disable

For more information, refer to the technical documentation on  Disabling a Physical Interface 

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

  Now observe the Aggregated Ethernet Interface Logical Interface line output (i.e. ae0.0).

Example:

root@switch> show interfaces ae0 terse 
Interface         Admin 	Link 	   Proto    Local       Remote
ae0               up    	down  
ae0.0             up   <<<<< 	down 	   eth-swith     

What is the 'Admin' status of the LAG Logical interface (i.e. ae0.0 in the example)?

• Up - Continue to Step 4
• Down - Bring the ae Logical Interface Administratively up with the command:
  
  root@switch# delete interfaces ae0 unit 0 disable

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

  Continue with Step 4 (when the ae0.0 Logical interface is Administratively Up).

  Run the following command to view all the Child Interface members associated with the Aggregated Ethernet Interface bundle:

root@switch> show interfaces terse | match <ae interface>

Note: This command is slightly different than the command used in the previous steps.

root@switch> show interfaces terse | match ae0     
ge-0/0/5.0       up    down aenet    --> ae0.0    <<<<<LAG Child Interface 
ge-0/0/6.0       up    up   aenet    --> ae0.0    <<<<<LAG Child Interface
</span>ae0              up    up  
ae0.0            up    up   eth-switch   

Are all the LAG Child Interface members of the Aggregated Ethernet Interface bundle listed?

• Yes - Continue to Step 5
• No - Configuration issue. Make sure all the expected LAG Child Interfaces are mapped to the right Aggregate Ethernet Interfaces.   To add a Child Interface member, refer to Step 4 in Configuring Aggregated Ethernet Interfaces (CLI Procedure) .

  Are the expected Child interfaces listed with the status of 'up up'? ('up up' means Administratively up and Link up)

root@switch> show interfaces terse | match ae0     
ge-0/0/5.0       up    up   aenet    --> ae0.0    <<<<<LAG Child Interface 
ge-0/0/6.0       up    up   aenet    --> ae0.0    <<<<<LAG Child Interface
</span>ae0              up    up  
ae0.0            up    up   eth-switch  

• Yes - Continue to Step 6
• No -  At least one LAG Child interface should be Active (Up/Up) to bring an Aggregate interface UP, by default.  Confirm that at least one LAG child interface in the Aggregated Ethernet bundle is Physically Up (Link status Up).

  For each Child Interface that is not 'up up', follow the steps in the Resolution Guide - EX - Verify/Troubleshoot Physical Interface to troubleshoot and correct it.

  Run the following command again:

show interfaces <ae interface> terse

Example:

root@switch> show interfaces ae0 terse 
Interface         Admin 	Link     Proto    Local    Remote
ae0               up    	down  
ae0.0             up    	down 	 eth-switch  <<<<<LAG Logical Interface </span>
 

• Yes - Continue to Step 7
• No or Not sure -
  The Aggregate Ethernet Interface ae0.0 is a Logical Interface.  It either must be configured as a Layer 2 (ethernet-switching) or Layer 3 (inet) Family.  For more information, refer to the technical documentation on  family (for EX Series switches).

  What is the 'Link' status of the ae interface (i.e. ae0)?

Example:

root@switch> show interfaces ae0 terse 
Interface         Admin 	Link 		Proto    Local                 Remote
ae0               up    	down  <<<<<
ae0.0             up    	down 	        eth-switch    

• Up - End of Workflow.   Your Aggregated Ethernet Interface has been verified as Up.  For example:

  root@switch> show interfaces terse | match ae0     
  ge-0/0/5.0       up    up   aenet    --> ae0.0   <<<<< LAG Child Interface
  ge-0/0/6.0       up    up   aenet    --> ae0.0   <<<<< LAG Child Interface
  ae0              up    up                  <<<<< LAG Parent Interface
  ae0.0            up    up   eth-switch     <<<<< LAG Logical Interface

1. LAG parent interface (ae0) and LAG logical interface (ae0.0) are Administratively Up
2. LAG parent interface (ae0) and LAG logical interface (ae0.0) are Link Up
3. Child interfaces (ge-0/0/5.0 and ge-0/0/6.0) are Administratively Up
4. Child interfaces (ge-0/0/5.0 and ge-0/0/6.0) are Link Up
5. The correct family is assigned to the LAG logical (ae0.0) interface

If you are having a problem with traffic not passing, then jump to Step 13 for some pointers.

• Down - Check the Aggregated Ethernet Minimum Links value on the Aggregated Ethernet Interface with the command "show interfaces ae0 | display set ".   You can configure the minimum number of links that must be up for the bundle to be labeled up. By default, only one link must be up for the bundle to be labeled up. For more information, refer to  Configuring Aggregated Ethernet Minimum Links. If the Administrator configured this parameter, then AE interface will not come-up until it satisfies the Minimum physical interface count.  
  Then continue to Step 8.

  Is this LAG interface a LACP (Link Aggregation Control Protocol)?

• No - If Aggregated Ethernet Interface is still not up, jump to Step 13 and contact your technical support representative.
• Yes - Continue to Step 9

  Run the following command to verify the LACP configuration between peers:

root@switch> show lacp interfaces

For an explanation of the fields below, refer to the documentation on  show lacp interfaces.

Working Example:

root@switch> show lacp interfaces             
Aggregated interface: ae0
    LACP state:       Role   Exp   Def  Dist  Col  Syn  Aggr  Timeout  Activity
      ge-0/0/5       Actor    No    No   Yes  Yes  Yes   Yes     Fast   Passive
      ge-0/0/5     Partner    No    No   Yes  Yes  Yes   Yes     Fast    Active
      ge-0/0/6       Actor    No    No   Yes  Yes  Yes   Yes     Fast   Passive
      ge-0/0/6     Partner    No    No   Yes  Yes  Yes   Yes     Fast    Active
    LACP protocol:        Receive State  Transmit State          Mux State 
      ge-0/0/5                  Current   Fast periodic Collecting distributing
      ge-0/0/6                  Current   Fast periodic Collecting distributing

Non-working Example:

root@switch> show lacp interfaces    
Aggregated interface: ae0
    LACP state:       Role   Exp   Def  Dist  Col  Syn  Aggr  Timeout  Activity
      ge-0/0/5       Actor    No    No   Yes  Yes  Yes   Yes     Fast    Active
      ge-0/0/5     Partner    No    No   Yes  Yes  Yes   Yes     Slow   Passive
      ge-0/0/6       Actor    No   Yes    No   No   No   Yes     Fast    Active
      ge-0/0/6     Partner    No   Yes    No   No   No   Yes     Fast   Passive
    LACP protocol:        Receive State  Transmit State          Mux State 
      ge-0/0/5                  Current   Slow periodic    Collecting distributing
      ge-0/0/6            Port disabled     No periodic           Detached

Is the Mux State for all the physical child interfaces equal to 'Collecting distributing'?   ('Collecting distributing' is the value you want to see.)

• No - Continue to Step 10
• Yes - Your Aggregated Ethernet Interface has been Verified as Up.  If traffic is not passing, continue to Step 13 for some pointers.

  For the physical interface in question, is the LACP Activity state set to Passive for both the Actor and Partner?

Non-working Example:

root@switch> show lacp interfaces    
Aggregated interface: ae0
    LACP state:       Role   Exp   Def  Dist  Col  Syn  Aggr  Timeout  Activity
      ge-0/0/5       Actor    No    No   Yes  Yes  Yes   Yes     Fast    Active
      ge-0/0/5     Partner    No    No   Yes  Yes  Yes   Yes     Slow   Passive
      ge-0/0/6       Actor    No   Yes    No   No   No   Yes     Fast    Active
      ge-0/0/6     Partner    No   Yes    No   No   No   Yes     Fast   Passive
    LACP protocol:        Receive State  Transmit State          Mux State 
      ge-0/0/5                  Current   Slow periodic    Collecting distributing
      ge-0/0/6            Port disabled     No periodic           Detached

• Yes - By default LACP Interfaces will be Passive interfaces. Passive means that it will not initiate LACP until it receives LACP packet from their Peer. Hence at least one end should be configured as 'Active' to initiate LACP.  Both sides can be configured as 'Active', but both sides cannot be set to 'Passive'.  Correct the configuration on one end.  For more information, refer to Configuring Aggregated Ethernet LACP.

• No - Continue to Step 11

  For the physical interface in question, is the Periodic Interval the same for both the Actor and Partner?

Non-working Example:

root@switch> show lacp interfaces 
Aggregated interface: ae0
    LACP state:       Role   Exp   Def  Dist  Col  Syn  Aggr  Timeout  Activity
      ge-0/0/5       Actor    No    No   Yes  Yes  Yes   Yes     Fast    Active  <<<<<
      ge-0/0/5     Partner    No    No   Yes  Yes  Yes   Yes     Slow   Passive  <<<<<
      ge-0/0/6       Actor    No    No   Yes  Yes  Yes   Yes     Fast    Active
      ge-0/0/6     Partner    No    No   Yes  Yes  Yes   Yes     Slow   Passive
    LACP protocol:        Receive State  Transmit State          Mux State 
      ge-0/0/5                  Current   Slow periodic Collecting distributing
      ge-0/0/6                  Current   Slow periodic Collecting distributing

• Yes - Continue to Step 12
• No - Configure both sides the same.  Then continue to Step 12.

  If all the physical interfaces are 'Collecting distributing' and you are experiencing issues with your Aggregated Ethernet Interface, also perform the following checks:

• Verify the EX switch child interfaces are connected to the correct Child Interfaces at the Far-end (Peer).
  • show interfaces ae0 extensive - To check the Partner's MAC address.  When LACP is negotiated, the LACP interface will display the learned Partner's MAC address.

• Verify the Partner's MAC address are in same OUI Range to make sure it is connected to the same device/chassis.

  If the problem is that traffic is not passing, investigate the following areas:

• MTU
• Typically, the MTU is left at the default setting. Check to see if it has been re-configured. The default MTU settings are as follows: Configuring the Media MTU
• STP (Spanning Tree Protocol)
  Verify STP with these Operational Mode Commands: Spanning Tree Operational Mode Commands.
• CoS (Class of Service)
  Verify CoS Services with these Operational Mode Commands: CoS Services Operational Mode Commands
• Check the current version: We recommend customers to use supported versions KB37530 [juniper.net]. https://supportportal.juniper.net/s/article/Juniper-recommendations-for-products-running-End-of-Support-EOS-software
• Traffic passing :
  Verify traffic is arriving and passing the EX switch with these tools:
  • Packet Capture
  • Monitor Interface

If it is still not resolved, contact your technical support representative.

2020-02-11: Article reviewed for accuracy; no changes required.
2022-04-21: Updated links, verified ELS outputs are the same. 

• KB22217 - Resolution Guides - EX - Troubleshoot/Verify Interface [juniper.net]