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  • 1.  QFX5120 switch consumes IIH

    Posted 07-19-2021 23:36

    I have a QFX5120-32C switch running 18.4R2-S5.4, the switch acts as bridge sitting in between two MX-routers where IS-IS is running over the connections,  the switch suddenly seems to be consuming IIH from the router to its RE 

    QFX5120-32C> monitor traffic interface et-0/0/11
    Listening on et-0/0/11, capture size 96 bytes

    02:42:27.628112 In IS-IS, p2p IIH, src-id 0101.0100.1010, length 57
    02:42:30.890840 In ES-IS, ISH, length 43

    QFX5120-32C> show configuration interfaces et-0/0/11
    description "facing ISIS router 1";
    unit 0 {
    family ethernet-switching {
    interface-mode access;
    vlan {
    members vlan-100;

    is this the right behavior of a switch? why would a switch RE needs to know anything about an IS-IS hello packets? how do I know wether the switch actually sent the original IIH copy to the other interface to egress out of the switch? (I won't be able to see this IIH frame going out with "monitor traffic interface" unless I do port mirroring on the other interface which I can not do). any clue?


  • 2.  RE: QFX5120 switch consumes IIH

    Posted 07-20-2021 09:53
    Seems a little odd, I wouldn't expect the switch to process the packet seeing as you don't have family ISO enabled. Can you monitor the interface on the MX end to see if you're receiving the hello via the QFX?

    Principal Engineer

  • 3.  RE: QFX5120 switch consumes IIH

    Posted 07-20-2021 10:40
    I consulted with a juniper expert, it is normal behavior, qfx-re is getting a copy of the multicasted IIH frame 

  • 4.  RE: QFX5120 switch consumes IIH

    Posted 07-20-2021 10:42
    ah cool, that's news to me. Thanks for confirming :)

    Principal Engineer

  • 5.  RE: QFX5120 switch consumes IIH

    Posted 08-16-2021 14:41
    This does not seem to be 'normal', since the switch should not be able to process ISO info if the interface does not have the address-family enabled, but some platforms just do this type of stuff. ; )