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[EX/QFX] Multi-chassis-protection configuration MC-LAG

  [KB33870] Show Article Properties


When ICCP and ICP-PL are running in separate links, a loop can be created if the multi-chassis-protection statement is misconfigured.

This article explains what should be done to prevent the loop from being created.



multi-chassis-protection is used to determine if the MC-LAG peer is up when ICCP goes down. If ICCP goes down, the peer with prefer-status-control-active will remain up, and the peer will change the lacp-system-id to the default to bring the interfaces down. This is to prevent split brain scenarios.

Most customers use a single ae bundle for ICCP and ICL-PL connections. In this scenario, customers configure the bundle as a multi-chassis-protection interface with no issues.

+---------------------+                 +-----------------------+
|                     | ae0 ICCP/ICL-PL |                       |
|  MC-LAG-PEER-A      +-----------------+  MC-LAG-PEER-B        |
|                     |                 |                       |
+---------------------+                 +-----------------------+

As per recommendation, some customers decide to have ICCP and ICL-PL running in separate links to prevent a single point of failure. The problem here is that when the ICCP interface (in this case ae0) is configured as a multi-chassis-protection interface, a loop is created since the MC-LAG peers will not know that ae1 is part of the MC-LAG and it will act as a regular trunk. 

+---------------------+      ae0 ICCP        +-----------------------+
|                     +----------------------+                       |
|  MC-LAG-PEER-A      |                      |  MC-LAG-PEER-B        |
|                     |      ae1 ICL-PL      |                       |
|                     +----------------------+                       |
|                     |                      |                       |
+---------------------+                      +-----------------------+

Due to this, during a fault scenario, you will see the MAC addresses learn in the ICL-PL with the flag DL (Dynamically local), when it should be DR (Dynamically remote).



To avoid this problem, configure ICL-PL (ae1) as the multi-chassis-protection interface.

#set multi-chassis-protection peer-ip-address interface ae1 


Modification History:

2019-04-22: Minor non-technical changes made


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