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Latency is abnormal on EX3400

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  • 1.  Latency is abnormal on EX3400

    Posted 03-02-2020 19:06

    I have 2 EX3400 switches that connected each other with a copper cable directly .

    When I did a ping test each other via  Lay2  or  Lay3 interface . The latency average was around 18ms.

    Also I connected a EX3400 to Cisco router (Huawei router ,Juniper EX4200 ) directly via Lay2 or Lay 3 . The latency average was around 15ms.

    But when I used two EX4200 switches to do the Ping test VIA L2 & L3 . The Latency was no more than 2ms .

    I don't know if this related to interface routing bridging (irb) on EX3400 .

    Anyone can help me with this ? Thx

    •  



  • 2.  RE: Latency is abnormal on EX3400

    Posted 03-02-2020 19:33

    Don't ping the switches directly on the IRB interfaces.  ICMP destined to the control plane on the 3400's is super low priority.   Try to ping actual hosts "through" the switch and you should have much better results. It's normal behavior, and your actual latency is not that high.



  • 3.  RE: Latency is abnormal on EX3400

    Posted 03-02-2020 20:40

    Hi damenten ,thank you very much . I got the better result when i did the ping through switches .

    But i still can't understand what you mean by "ICMP destined to the control plane on the 3400's is super low priority."

    As usual we need to do the ping on switches to check the backbone quality  . If we do ping "through swithes ",that way ,we need invest more devices . Any other ways to aviod this or  any official document that i can refer to ? THANKS



  • 4.  RE: Latency is abnormal on EX3400
    Best Answer

     
    Posted 03-02-2020 21:18

    Hi

     

    When the icmp ping is destined towards the local interface of the switch, by design this packet processing will happen at the routing engine (control plane) and hence the priority of processing this kind of packet is very low on all the devices. Hence you will see latency in the ping towards an irb interface or local L3 interface.

    However you will not notice that latency if the icmp is through the switch that is via data plane as it will be switches in the hardware.

     

    Refer to the below KB for more clarity

     

    https://kb.juniper.net/InfoCenter/index?page=content&id=KB28157

     

     



  • 5.  RE: Latency is abnormal on EX3400

    Posted 03-02-2020 22:07

    Hi, Thanks . I reviewed the article . It seems to be a result of design of Juniper platform. but Do you know any commands or ways to slove ?

     

     



  • 6.  RE: Latency is abnormal on EX3400

     
    Posted 03-02-2020 22:15

    Hi 

     

    As you said this is how the platform is designed so we cannot change/modify the processing behavior using commands.