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MC-LAG must have ICL - Why?

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  • 1.  MC-LAG must have ICL - Why?

    Posted 09-19-2017 12:43

    Hi

     

    Every scenario I see with Junos MC-LAG requires a ICL link and the MC-AE interface has to be L2.  If you want L3 you need to back this off to a irb interface.

     

    I have the situation where I need to achieve the following:

     

    multiple downstream devices, each using the same two vlan IDs.  but each ae interface uses a different L3 subnet on vlans.

     

    example:

    client 1:

    vlan 10 = 10.1.1.2/30

    vlan 20 = 10.2.1.2/30

     

    client 2:

    vlan 10 = 10.1.1.6/30

    vlan 20 = 10.2.1.6/30

     

    on my MC-LAG peers I want to put all vlan 10 interfaces into one L3VPN and all vlan 20 interfaces into another L3VPN.

     

    on my cisco boxes I have mc-lag in active/standby and the following type of config:

     

     

    int gi1
      lacp fast
      bundle id AAA active
    
    int gi1.10 
      vrf forwarding L3VPN-A
      ipv4 address 10.1.1.2/30
    
    int gi1.20
       vrf forwarding L3VPN-B
       ipv4 address 10.2.1.2/30
    
    int gi2
      lacp fast
      bundle id BBB active
    
    int gi2.10
      vrf forwarding L3VPN-A
      ipv4 address 10.1.1.6/30
     
    int gi1.20
       vrf forwarding L3VPN-B
       ipv4 address 10.2.1.6/30
    

    now as the Cisco is running active/standby only the active router is announcing the routes into the VRF.

     

    on my Junos MX platforms I am wondering if I can do the same.

    all examples seem to indicate I need to backoff the L3 interfaces onto IRBs.  This for me means the following complications:

    1.  having to dedicate a VLAN per downlink vlan so that I can have the unique /30 subnets.

    2.  having to have vlan rewrites from the internal vlans down to the standardised vlans facing the clients.

    3.  having to place all of those internal vlans onto the ICL interface.

     

    I can understand that if I wanted an active/active setup with state sync etc I may need to do these tricks, but is it needed for active/standby?

     

    many thanks


    #mx
    #mc-lag
    #active
    #L3unicast
    #standby


  • 2.  RE: MC-LAG must have ICL - Why?
    Best Answer

    Posted 09-20-2017 01:16

    Hello,

    I'll give it a stab Smiley Happy

     


    @William.jackson@gibtele.com wrote:

    Hi

     

    Every scenario I see with Junos MC-LAG requires a ICL link 


    Technically ICL is only required for A/A MC-LAG. This is spelled out in Juniper MC-LAG tech doc

    https://www.juniper.net/documentation/en_US/junos/topics/concept/mc-lag-feature-summary-best-practices.html

     

    The interchassis link (ICL), also known as the interchassis link-protection link
    (ICL-PL), is used to forward data traffic across the MC-LAG peers. This link
    provides redundancy when a link failure (for example, an MC-LAG trunk failure)
    occurs on one of the active links.

    "one of the active" means both legs of the MC-LAG are active, a.k.a. A/A MC-LAG.

    In A/S MC-LAG, You certainly can live without ICL  but ask Yourself a question - what would You do if later on Your design changes and You suddenly need A/A MC-LAG? Scramble to invest in ICL pronto? What if MC-LAG peers are dozens of miles apart?

     


    @William.jackson@gibtele.com wrote:

    Hi

     

     If you want L3 you need to back this off to a irb interface.

     

     


    On MX series, You can use L3 subinterfaces with A/S MC-LAG in JUNOS 11.4R6 and later, this was fixed via confidential PR 804507.

    For A/A MC-LAG, on all platforms, you still need IRB with VRRP.

    HTH

    Thx

    Alex

     



  • 3.  RE: MC-LAG must have ICL - Why?

    Posted 01-30-2018 12:20


    HI,

     

    Have you guys tested failing over by shutting down the ICL interface? The mc-lag member port of the peer PE goes down alone with the ICL interface. However, the "status-control standby" interface stays down and I have to bounce it to bring it back up


    Thanks,

     

    M