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ICL and ICCP link, what VLAN configuration

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  • 1.  ICL and ICCP link, what VLAN configuration

    Posted 06-20-2019 07:21


    I'm currently working with MC-LAG to get a test environment running. Unfortunately i cant get my head around one part of the configuration.


    I have 4 switches, two at top and the other two connected with those switches by MC-LAG.


    Switch A - - - Switch B

        |                             |

    Switch C - - - Switch D


    Now both stacks are configured with MC-LAG and i've separate interfaces for the ICCP (ae1) traffic and ICL-PL (ae2).

    The ICCP traffic is configured to connect with the Lo0 of their neighbour and between Switch A and Switch B there is a routing-vlan with on both sides an IRB interface on VLAN 1.


    Now i also have a ICL link, which has a different VLAN and is connected directly by a fibre. On both ends again an IRB interface on VLAN 2.


    Both stacks are connected with each other with vlan 100 and this is used for routing purposes (ospf.) 

    There are also some tagged vlans who are just stretched.


    My question is, do i need to configure those stretched vlans etc on the ICL-PL link so that mac-sync etc is done? Or is connectivity between those links enough? For now i've configured those vlans as tagged on the same link as ICCP is connected over (ae1.) 


    I cannot find a good answer in the Juniper documentation about the ICL-PL link and it's configuration.


  • 2.  RE: ICL and ICCP link, what VLAN configuration

    Posted 06-20-2019 07:55



    First of all, I'd like to inform you that the MC-LAG configuration and topology assume 3 devices:

    1) One device has regular (traditional) configuration for AE-interface.

    2) Other two devices must have a configuration related to MC-LAG.


    In your configuration, switchC must have a connection to switchB and switchD must have connection to switchA.

    You don't need a connection between SwitchC and SwitchD.


    Please use this link as a reference.

  • 3.  RE: ICL and ICCP link, what VLAN configuration

    Posted 06-20-2019 09:04

    Thanks for your answer.

    That would mean that i cannot connect two stacks of MC-LAG (stack of A/B and the stack of C/D) with each other?

    Port 1 of switch A and C are connected and configured as AE1 on each device. Port 1 of Switch B and D are also configured with AE1. All AE1 ports are configured for MCAE functionality. 


  • 4.  RE: ICL and ICCP link, what VLAN configuration
    Best Answer

    Posted 06-20-2019 09:29

    The concept of MC-LAG is to avoid a single point of failure where a server is connected to an access switch. Hence, the LAG from the server is split between two upstream switches appearing as a single switch to the Server. The same concept can be implemented between different layers in the Data-center Architecture. In your test environment, Switch C having a LAG interface AE1 with two links, with one link terminating at Switch A and the other at Switch B and Switch A&B running MC-LAG. The same can be with the Switch D connecting to both Switches A & B.

    To answer your questions, you need to configure your ICL-PL link as trunk with family ethernet-switching with all the stretched VLANS to allow data traffic but not mac-sync. Your ICCP has to be a L3 link as TCP communication is required for ICCP. These ICCP and ICL-PL links will between Switch A and Switch B.

    I would suggest you to refer through the documents at the links below for better understanding of the usage and working of MC-LAG with examples.


    Configuration example: https://www.juniper.net/documentation/en_US/release-independent/nce/topics/example/multichassis-link-aggregation-ex9200-series.html

    Please Mark My Solution Accepted if it Helped, Kudos are Appreciated too!!!

    Juniper Internal

  • 5.  RE: ICL and ICCP link, what VLAN configuration

    Posted 06-20-2019 10:01

    Thanks for the links and explaination.

    Does anyone know if there is a "best practice" somewhere considering connecting two MC-LAG stacks?

    Can it be done without the link between switch A and C? (the cross links)

  • 6.  RE: ICL and ICCP link, what VLAN configuration

    Posted 06-20-2019 11:46



    i would advise best practice is to connect the cross links for a back to back MC-LAG, I have seen however several instances of this working just fine without the cross links. I have had cases of customers running it like this with no problems specific to the absence of the links even big clients.


    so is it possible? yes absolutely.

  • 7.  RE: ICL and ICCP link, what VLAN configuration

    Posted 06-21-2019 01:28

    I tried to draw a picture for you. The topology from picture that is all is the "best practice".

    For ICCP and ICL you can use one link or two separete links.Screenshot 2019-06-21 at 10.25.29.png

  • 8.  RE: ICL and ICCP link, what VLAN configuration

    Posted 06-23-2019 23:31

    Thanks for this! 

  • 9.  RE: ICL and ICCP link, what VLAN configuration

    Posted 06-20-2019 09:37

    @HGW - MC-LAG and VC are mutually conflicting, and can not be run at same time on same product/node/stack.  Junos OS does allow for such a configuration, but it will not work, or be supported.

  • 10.  RE: ICL and ICCP link, what VLAN configuration

    Posted 06-20-2019 16:10

    I'm not entirely clear on the question but this thread may be helpful.