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ex and cisco stp interoperability

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  • 1.  ex and cisco stp interoperability

    Posted 02-22-2018 06:34

    Hello to All,


    Topic: stp interoperability between cisco and ex swithc.

    ref: https://www.juniper.net/us/en/local/pdf/implementation-guides/8010002-en.pdf

    I already read different forum and juniper  documentation about this topic and at the end it is valid that:


    1)cisco side -> pvstp

    2)ex side -> rstp

    The above combination should work just fine (except in changing the path cost calculation cisco´s side )

    Based on https://www.juniper.net/us/en/local/pdf/implementation-guides/8010002-en.pdf, what is happening is that:

    1) juniper´s side simply ignore the bpdu-pvstp sent by the cisco  and consider them like normal multicast traffic. 

    2) juniper´s side is recognizing as standard bpdu the muticast 01:80:C2:00:00:00 bpdu (vlan 1).


    "(...)Since RSTP only has a single Spanning Tree instance for all VLANs across a trunk and there is no vlan awareness, all traffic will be forwarded or blocked based on the VLAN1 topology."


    All good. 

    I have now the following case:



    cisco switch "distribution" layer  (pvstp)

    MAC xxxx.xxxx.3d80, priority 32768









    ex switch "access" layer (rstp)

     MAC xxxx.xxxx.8441 , priority 61440



    1)configure vlan 9 on both swicthes

    2)I create also the vlan1 on ex side

    3)configuration interface on ex-side


    set interfaces ge-0/0/47 unit 0 family ethernet-switching port-mode trunk
    set interfaces ge-0/0/47 unit 0 family ethernet-switching vlan members 9
    set interfaces ge-0/0/47 unit 0 family ethernet-switching native-vlan-id 1

    4)configuration interface on cisco sdie

    interface FastEthernet1/0/8
     switchport trunk encapsulation dot1q
     switchport trunk allowed vlan 9
     switchport mode trunk


    1)ex side

    Spanning tree interface parameters for instance 0
    Interface    Port ID    Designated      Designated         Port    State  Role
                             port ID        bridge ID          Cost
    ge-0/0/47.0    128:560      128:560  61440.xxxx.xxxx.8441    200000  FWD    DESG


    2)cisco side

    show spanning-tree vlan 9
      Spanning tree enabled protocol ieee
      Root ID    Priority    32777
                 Address     xxxx.xxxx.3d80
                 This bridge is the root
                 Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec
      Bridge ID  Priority    32777  (priority 32768 sys-id-ext 9)
                 Address   xxxx.xxxx.3d80
                 Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec
                 Aging Time  300 sec

    Interface           Role Sts Cost      Prio.Nbr Type
    ------------------- ---- --- --------- -------- --------------------------------
    Fa1/0/8             Desg FWD 19        128.10   P2p

    I was expecting to see the cisco as root but as you can see I have basically 2 different root and this is not the wished result.

    Any hint here?

    Thank you.

    Thank you.


  • 2.  RE: ex and cisco stp interoperability
    Best Answer

    Posted 02-22-2018 07:33
      |   view attached

    Why not just use VSTP config option, set protocols vstp vlan "X" instead?  VSTP was designed by Juniper to allow interoperability with non-standard PVSTP/PVSTP+ from Cisco.  For + you might need both vstp and rstp configured at same time.


    Not sure which model EX you are trying this with (always good idea to include both model and SW version), but below is link to newer ELS model discussion of STP Options:




    I am also attaching an old (but good) document regarding 3rd-party interoperability testing between Juniper and Cisco.


    Good luck, hope this helps.


    Cisco_cookbook[1].pdf   15.87 MB 1 version

  • 3.  RE: ex and cisco stp interoperability

    Posted 02-22-2018 07:52

    Thank you for your reply but I want to test and make it working exaclty this combination

    RSTP on EX and PSTP+ on cisco.


    Only after that I will try different combination.




    JUNOS Base OS boot [12.3R9.4]


    and in any case also in your coockbook the combiation rstp and pvstp+it works just fine.

  • 4.  RE: ex and cisco stp interoperability

    Posted 02-26-2018 03:14


    I will close the topic and yes to have interoperability PVSTP and Juniper, as in my case, is needed to configure in juniper side the rstp and vstp as per