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MC-LAG Layer 3 unicast functionality?

  • 1.  MC-LAG Layer 3 unicast functionality?

    Posted 10-21-2020 08:59

    Hi all,

     

    Based on this url https://www.juniper.net/documentation/en_US/junos/topics/topic-map/mc-lag-high-availability-l3-vrrp-macsync.html#id-example-configuring-multichassis-link-aggregation-for-layer-3-unicast-using-mac-address-synchronization

     

    "You can choose either to synchronize the MAC addresses for the Layer 3 interfaces of the switches participating in the MC-LAG, or you can configure Virtual Router Redundancy Protocol (VRRP), but you cannot configure both at the same time."

     

    It said cannot use at same time. But when i look on config on that url the "mcae-mac-synchronize" was tie into irb interface. So it should not have issue right if we mix in one MC-LAG interface with VRRP and mcae-mac-synchronize with different irb? For example irb.40 i'm use VRRP method and irb.50 i'm use mcae-mac-synchronize method.

     

    Thanks and appreciate any feedback.

     

     



  • 2.  RE: MC-LAG Layer 3 unicast functionality?

     
    Posted 9 days ago
    That's an interesting questions!!! 

    I've tested MC-LAG extensively, but never tested having both VRRP and mcae-mac-synchronize at the same time as you mentioned.  I cannot  think of a reason why it would not work, BUT I would test it carefully before implementing it in production.   I would look closely at loop avoidance, and failover under different failure scenarios.  

    Regards, 


    ------------------------------
    Yasmin Lara
    Juniper Ambassador
    JNCIE-SP, JNCIE-ENT, JNCIE-DC, JNCIE-SEC
    JNCDS-DC, JNCIA-DevOps, JNCIP-CLOUD, CCNP-ENT
    ------------------------------



  • 3.  RE: MC-LAG Layer 3 unicast functionality?

    Posted 6 days ago
    Hi, it's better to identify first if you really need this type of configuration mix. Here are some recommendations and notes on using VRRP and mac-address synchronization:

    https://www.juniper.net/documentation/en_US/junos/topics/concept/best-practices-usage-notes.html#jd0e493

    This document was really helpful when I've started configuring different features with MC-LAG installation.

    ------------------------------
    Regards,
    Elchin
    ------------------------------



  • 4.  RE: MC-LAG Layer 3 unicast functionality?

    Posted 14 hours ago
    Hi E.K.H,


    Based on  url that u given, the caveat below referring to IGP right? So if from CE just have default route/static and from MC-LAG have default/static to CE then it should have no issue right?

    "Note

    Here are some caveats with configuring MAC address synchronization:

    • Use MAC address synchronization if you are not planning to run routing protocols on the IRB interfaces.

      MAC address synchronization does not support routing protocols on IRB interfaces, and routing protocols are not supported with downstream MC-LAG clients. If you need routing capability, configure both VRRP and routing protocols on each MC-LAG peer. Routing protocols are supported on upstream routers."



    Appreciate any feedback



  • 5.  RE: MC-LAG Layer 3 unicast functionality?

    Posted 6 hours ago
    Hi kronicklez,

    There is no mentioning about usage of dynamic or static routing protocols, so it should be applied to both and you need to configure each member of MC-LAG separately with routing configuration. Here is an example:

    QFX1
    set interfaces irb unit 153 family inet address 172.31.53.2/24 vrrp-group 53 virtual-address 172.31.53.1
    set interfaces irb unit 153 family inet address 172.31.53.2/24 vrrp-group 53 priority 200
    set interfaces irb unit 153 family inet address 172.31.53.2/24 vrrp-group 53 accept-data
    set routing-options static route 172.31.50.31/32 next-hop 172.31.53.31

    show route 172.31.53.31
    172.31.53.0/24 *[Direct/0] 3w4d 18:31:53
    > via irb.153



    QFX2
    set interfaces irb unit 153 family inet address 172.31.53.3/24 vrrp-group 53 virtual-address 172.31.53.1
    set interfaces irb unit 153 family inet address 172.31.53.3/24 vrrp-group 53 priority 150
    set interfaces irb unit 153 family inet address 172.31.53.3/24 vrrp-group 53 accept-data
    set routing-options static route 172.31.50.31/32 next-hop 172.31.53.31

    show route 172.31.53.31
    172.31.53.0/24 *[Direct/0] 3w4d 18:32:08
    > via irb.153

    So each of the members will be able to communicate over directly connected interface in this case.

    Also based on the documentation:

    There are two methods for enabling Layer 3 unicast functionality across a multichassis link aggregation group (MC-LAG) to control traffic flow. You can choose either to synchronize the MAC addresses for the Layer 3 interfaces of the switches participating in the MC-LAG , or you can configure Virtual Router Redundancy Protocol (VRRP), but you cannot configure both at the same time. Because RVI interfaces share the same MAC address, if you enable MAC address synchronization, packets received on an MC-LAG peer with a destination MAC address that is the same as that of the peer's IRB MAC address will not be forwarded.

    I think last statement clearly defines the reason, why this two statements should not being configured at the same time.

    Note
    On QFX5100 and QFX10000 switches, if you try to configure both VRRP over IRB and MAC synchronization, you will receive a commit error.

    ------------------------------
    Regards,
    Elchin
    ------------------------------



  • 6.  RE: MC-LAG Layer 3 unicast functionality?

    Posted 5 hours ago
    Hi EK.H,


    Noted. But in my situation is MX480.  One more thing, may i know how u do packet capture in MC-LAG environment? Coz in MC-LAG it will use family bridge. Also when u use MC-LAG  on MX is there any MTU decrease by automatically due to family bridge/irb.?

    Thanks and appreciate your advise.