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  • 1.  More questions about EVPN multihome configuration

    Posted 04-04-2021 21:57
    I have struggled for two days without figuring out how to do what I need.

    I come down to the following simple topology.

    My understanding is ESI controls which vtep forwards BUM traffic to CE which is L2 switch here.
    The training I took and the Docs I read discuss the LAG on the CE device, I do not have LAG here, just a L2 switch connected to two VTEPs.  Any difference here ?
    When I configured ESI here as follows:
    root@vtep-1# show | display set | match esi 
    set interfaces xe-0/0/0 esi 00:01:01:01:01:01:01:01:01:02
    set interfaces xe-0/0/0 esi all-active
    
    root@vtep-2# show | display set | match esi 
    set interfaces xe-0/0/1 esi 00:01:01:01:01:01:01:01:01:02
    set interfaces xe-0/0/1 esi all-active
    ​

    I do not see any vtep as a backup forwarder which I saw in my previous training lab where the ae0 interface is used.  Are they different ?
    This following is what I saw here for this topology

    root@vtep-1# run show evpn instance designated-forwarder 
    Instance: default-switch
      Number of ethernet segments: 4
        ESI: 00:01:01:01:01:01:01:01:01:02
          Designated forwarder: 10.68.191.233
        ESI: 05:00:00:ff:fe:00:00:03:e8:00
        ESI: 05:00:00:ff:fe:00:00:04:08:00
        ESI: 05:00:00:ff:fe:00:00:04:4c:00
    
    {master:0}[edit]
    root@vtep-1# run show evpn instance backup-forwarder        
    Instance: default-switch
      Number of ethernet segments: 4
        ESI: 00:01:01:01:01:01:01:01:01:02
        ESI: 05:00:00:ff:fe:00:00:03:e8:00
        ESI: 05:00:00:ff:fe:00:00:04:08:00
        ESI: 05:00:00:ff:fe:00:00:04:4c:00
    
    root@vtep-2# run show evpn instance designated-forwarder 
    Instance: default-switch
      Number of ethernet segments: 5
        ESI: 00:01:01:01:01:01:01:01:01:01
        ESI: 00:01:01:01:01:01:01:01:01:02
          Designated forwarder: 10.68.191.205
        ESI: 05:00:00:ff:fe:00:00:03:e8:00
        ESI: 05:00:00:ff:fe:00:00:04:08:00
        ESI: 05:00:00:ff:fe:00:00:04:4c:00
    
    {master:0}[edit]
    root@vtep-2# run show evpn instance backup-forwarder        
    Instance: default-switch
      Number of ethernet segments: 5
        ESI: 00:01:01:01:01:01:01:01:01:01
        ESI: 00:01:01:01:01:01:01:01:01:02
        ESI: 05:00:00:ff:fe:00:00:03:e8:00
        ESI: 05:00:00:ff:fe:00:00:04:08:00
        ESI: 05:00:00:ff:fe:00:00:04:4c:00
    
    

    Another question is BUM from VTEP-5 is forwarded by the designated forwarder to L2 switch, the L2 switch then forwards it to another VTEP-X which sends it back VTEP-5. How to prevent this ?

    thanks a lot for coaching !!!!





  • 2.  RE: More questions about EVPN multihome configuration

    Posted 04-04-2021 22:38
    I figured out the backup forwarder.  The DR election is via bgp session.  I did not peer vtep-1 and vtep2. That is why.


  • 3.  RE: More questions about EVPN multihome configuration

    Posted 04-04-2021 23:23
    Another question is BUM from VTEP-5 is forwarded by the designated forwarder to L2 switch, the L2 switch then forwards it to another VTEP-X which sends it back VTEP-5. Is this possible ?  How to prevent this ?

    thanks a lot for coaching !!!!


  • 4.  RE: More questions about EVPN multihome configuration

    Posted 04-04-2021 23:35
    I found this nice thread  https://community.juniper.net/communities/community-home/digestviewer/viewthread?MID=73558

    If a bridged network is multihomed to more than one PE in an EVPN network via switches, then the support of All-Active redundancy mode requires the bridged network to be connected to two or more PEs using a LAG.

     Does this mean I have to provide loop prevention on that L2 switch ?

    thanks a lot for any commands !!



  • 5.  RE: More questions about EVPN multihome configuration

    Posted 04-05-2021 04:55
    You need to look at the problem from the point of view of the switch that you have attached to VTEP1 and VTEP2.

    If this was a normal STP network there would be a ROOT port and a BLOCKED port from that switch into the rest of the network.

    I think there is the potential for the situation you have described :
    "Another question is BUM from VTEP-5 is forwarded by the designated forwarder to L2 switch, the L2 switch then forwards it to another VTEP-X which sends it back VTEP-5. Is this possible ? ".  

    I think that this again depends on the edge switch setup.  If that edge switch has both links in a forwarding state as separate links ( not a LAG ) that you could re-circulate the BUM traffic.

    I would say that if you want all-active = use a LAG and if you dont/cant use a LAG then set your ESI to active-standby.

    The downside to the A/S is a reduction in bandwidth and a very small failover time for the BGP convergence if the active fails.



    ------------------------------
    William Jackson
    ------------------------------



  • 6.  RE: More questions about EVPN multihome configuration

    Posted 04-05-2021 09:58
    thanks so much !!
    I can't change that switch deployment and can't use LAG either. So I am any other possible approach if possible.

    Do you know whether QFX supports ESI A/S ?   As I know, QFX does not support A/S, right ?


  • 7.  RE: More questions about EVPN multihome configuration

    Posted 04-05-2021 10:14
    QFXx ONLY support A/A!!


  • 8.  RE: More questions about EVPN multihome configuration

    Posted 04-05-2021 10:21
    thanks for confirming this !!