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Layer 2 traffic over GRE tunnel and Loop prevention mechanism

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  • 1.  Layer 2 traffic over GRE tunnel and Loop prevention mechanism

    Posted 08-09-2017 07:04

    Hi everybody,

     

    I am reading this great link on bridging layer2 over GRE tunnel on Juniper MX:

    https://kb.juniper.net/InfoCenter/index?page=content&id=KB31139

     

    I am wondering if there is any loop prevention such as Split horizon when bridging layer2 over GRE.

     

    For example:

     

     We have three  PE1,PE2,PE3 ; we have configured GRE tunnels among them so they are fully meshed over GRE tunnel, these tunnels will be used to carry layer2 traffic from connected CE.

    Next we configured Bridge-domain on al three PE and placed GRE tunnels in it.

    Now let say PE1 receives a frame from attached CE, destination MAC is FFFF.FFFF.FFFF , PE1 will forwards these frame over GRE tunnels to PE2 and PE3, now what will PE2 or PE3 do?

     

    Will they turn around and send it over to PE1 and thus creating a loop or we have split horizon just like we have for VPLS where Frame received on PW will not be transmitted to another PE over another PW?

     

     

    Thanks and have a nice day!!



  • 2.  RE: Layer 2 traffic over GRE tunnel and Loop prevention mechanism
    Best Answer

    Posted 08-09-2017 07:25

    NO, no loop prevention at all

    regarding STP.protocol frames I did not test ( was not necessary in the project where I tested and verified the feature)

     

    This is a very simple tunneling of Layer 2 frames over GRE and a "buggy" implementation regarding fragmentation, and inclusion of layer 2- control protocols, so as well on the attached bridge-group and on the GRE interface OAM is not implemented (even MEP up from any other interface of that bridge-group does not work when the partner mep is over the L2-GRE tunnel), GRE-keepalive also does not work due to missing L3-address for BFD.

     

    also take care that exactly that config from the KB DOES NOT work, when configuring a GRE tunnel key, the L2 over GRE stops working, so if you try leave out the GRE tunel key

     

    regards

     

    alexander



  • 3.  RE: Layer 2 traffic over GRE tunnel and Loop prevention mechanism

    Posted 08-09-2017 08:03

    Thanks for your response, If you do not mind, could you please tell us JUNOS Version and platform you tried that feature?

     

     



  • 4.  RE: Layer 2 traffic over GRE tunnel and Loop prevention mechanism

    Posted 08-09-2017 09:08
    It was MX80, MX240 and MX960 from 16.1 to 17.1 various versions

    Not all versions were tested by me, but by other company and we exchanged
    experiences.



    Regards



    alexander


  • 5.  RE: Layer 2 traffic over GRE tunnel and Loop prevention mechanism

    Posted 08-09-2017 09:53

    Thanks