Routing

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Multicast routing PIM L3 switches No PIM interfaces configured

  • 1.  Multicast routing PIM L3 switches No PIM interfaces configured

    Posted 08-20-2021 16:59
    Hiya

    I studied PIM a while ago and the new company Im working at is using multicast for video streaming.

    The have configured the core switch to be the RP and are then advertising several multicast groups(subnets) and the RP via a routing instance.

    They are using OSPF for the routing between the L3 switches so all switches are aware of the multicast groups and RP.

    I have run show pim interfaces on many of the L3 switches and it say the pim instance does not exist, in other words the switches havent been enabled for PIM

    Some how they are still routing multicast traffic. Would this be because the receives look at their local switch (and has the routes) will route to the RP regardless.

    I would have thought there would be a PIM tree if it is not enabled on any of these switches.

    Thanks

    ------------------------------
    MIKE WRIGHT
    ------------------------------


  • 2.  RE: Multicast routing PIM L3 switches No PIM interfaces configured

    Posted 08-22-2021 13:06
    Hi Mike,

    Is hard to say what is going on without knowing further details, but below are a few items to have in mind if you want to broaden your knowledge of the multicast topology in your routing domain:

    a. Identify the First Hop Router (FHR) and the Last Hop Routers (LHR) - By doing so, you will be able to know the edge of the multicast domain at each extreme of the network, identifying upstream (SOURCE) and downstream (RECEIVER) devices.
    b. By knowing (a), you will also know which switches SHOULD be running Protocol Independent Multicast (PIM) in your topology, therefore predict devices that should be only operating at L2 from a multicast perspective without requiring PIM to route multicast and only Internet Group Message Protocol (IGMP).
    c. Identify the multicast distribution tree (MDT) in place in the network - By doing so, you will be able to know what are the mechanisms Protocol Independent Multicast (PIM) will use in order to resolve the multicast topology.

    Now, you could discovery all these items by simply doing a 'show pim topology <GROUP>' and identifying the outgoing interfaces (OIL) of the group, which indicate where the interested RECEIVERs are, and the incoming interface (IL) which identify where the SOURCEs reside, by doing this, you will know how the source and shared trees are getting constructed from the source and the RP, therefore having a deeper understanding of what is going on in your multicast routing domain.

    HTH,

    Elvin


  • 3.  RE: Multicast routing PIM L3 switches No PIM interfaces configured

    Posted 08-22-2021 13:06
    Hi Mike, 

    Initially, the multicast traffic is tunneled from the sending side router to the RP as unicast traffic with destination address = RP.  That could get to the RP without PIM enabled on the interfaces.  However, on the receiving side, the router that receives an IGMP message from the client, sends PIM join message towards the RP, and that requires PIM enabled interfaces all the way to the RP.   

     My guesses:
    - The switches are flooding the multicast traffic (at L2) 
    - You are using something like draft rosen and the multicast traffic is being encapsulated in GRE. 

    Regards, 






    ------------------------------
    YASMIN LARA
    Technical Marketing Engineer
    JNCIE-SP, JNCIE-ENT, JNCIE-DC, JNCIE-SEC
    JNCDS-DC, JNCIA-DevOps, JNCIP-CLOUD
    ------------------------------



  • 4.  RE: Multicast routing PIM L3 switches No PIM interfaces configured

    Posted 08-22-2021 21:33
    Hiya Yasmin

    What you are saying in your initial paragraph seems right to me.

    We basically only have RP and groups being advertised in routing instance.

    My opinion is this is a poor configuration, do you confirm.

    Regards

    ------------------------------
    MIKE WRIGHT
    ------------------------------



  • 5.  RE: Multicast routing PIM L3 switches No PIM interfaces configured

    Posted 08-22-2021 21:32
    Could it just be that the PIM is within an instance, that is you may have forgotten the «instance all» at the end of «show pim interfaces» ? :)

    ------------------------------
    Olivier Benghozi
    ------------------------------



  • 6.  RE: Multicast routing PIM L3 switches No PIM interfaces configured

    Posted 08-23-2021 08:40
    Going into more obscure scenarios, if for some reason in the initial process while the SOURCE is registering to the RP, the PIM Join from RP back to the FHR does not arrive and/or the RP never sends the PIM Register Stop, certainly the FHR would stay sending multicast traffic encapsulated as unicast, never switching to the native multicast path, and in this situation the only parties that would know what's going on in terms of multicast groups in your L3 topology are the path from the RP down to the RECEIVERs and the path from the SOURCE towards the RP, the routers in transit from SOURCE (FHR) to RP won't know, but that is usually due to configuration issues or software defects.

    More plausible scenarios could be due to tunneling as mentioned by Yasmin, or something like Multicast VLAN Registration (MVR).

    Regards,

    Elvin


  • 7.  RE: Multicast routing PIM L3 switches No PIM interfaces configured

    Posted 08-23-2021 09:13
    Configuration now understood. Pim is enabled they are using virtual routing/instances

    Thanks

    On Mon, 23 Aug 2021, 13:39 via Juniper Networks, <Mail@community.juniper.net> wrote:
    Going into more obscure scenarios, if for some reason in the initial process while the SOURCE is registering to the RP, the PIM Join from RP back... -posted to the "Ask the Expert" community
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    Re: Multicast routing PIM L3 switches No PIM interfaces configured
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    ElvinArias
    Aug 23, 2021 8:40 AM
    ElvinArias
    Going into more obscure scenarios, if for some reason in the initial process while the SOURCE is registering to the RP, the PIM Join from RP back to the FHR does not arrive and/or the RP never sends the PIM Register Stop, certainly the FHR would stay sending multicast traffic encapsulated as unicast, never switching to the native multicast path, and in this situation the only parties that would know what's going on in terms of multicast groups in your L3 topology are the path from the RP down to the RECEIVERs and the path from the SOURCE towards the RP, the routers in transit from SOURCE (FHR) to RP won't know, but that is usually due to configuration issues or software defects.

    More plausible scenarios could be due to tunneling as mentioned by Yasmin, or something like Multicast VLAN Registration (MVR).

    Regards,

    Elvin
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    Original Message:
    Sent: 8/23/2021 5:23:00 AM
    From: ElvinArias
    Subject: RE: Multicast routing PIM L3 switches No PIM interfaces configured

    Going into more obscure scenarios, if for some reason in the initial process while the SOURCE is registering to the RP, the PIM Join from RP back to the FHR does not arrive and/or the RP never sends the PIM Register Stop, certainly the FHR would stay sending multicast traffic encapsulated as unicast, never switching to the native multicast path, and in this situation the only parties that would know what's going on in terms of multicast groups in your L3 topology are the path from the RP down to the RECEIVERs and the path from the SOURCE towards the RP, the routers in transit from SOURCE (FHR) to RP won't know, but that is usually due to configuration issues or software defects.

    More plausible scenarios could be due to tunneling as mentioned by Yasmin, or something like Multicast VLAN Registration (MVR).

    Regards,

    Elvin
    Original Message:
    Sent: 08-22-2021 14:19
    From: MIKE WRIGHT
    Subject: Multicast routing PIM L3 switches No PIM interfaces configured

    Hiya Yasmin

    What you are saying in your initial paragraph seems right to me.

    We basically only have RP and groups being advertised in routing instance.

    My opinion is this is a poor configuration, do you confirm.

    Regards

    ------------------------------
    MIKE WRIGHT

    Original Message:
    Sent: 08-21-2021 22:52
    From: Yasmin Lara
    Subject: Multicast routing PIM L3 switches No PIM interfaces configured

    Hi Mike, 

    Initially, the multicast traffic is tunneled from the sending side router to the RP as unicast traffic with destination address = RP.  That could get to the RP without PIM enabled on the interfaces.  However, on the receiving side, the router that receives an IGMP message from the client, sends PIM join message towards the RP, and that requires PIM enabled interfaces all the way to the RP.   

     My guesses:
    - The switches are flooding the multicast traffic (at L2) 
    - You are using something like draft rosen and the multicast traffic is being encapsulated in GRE. 

    Regards, 






    ------------------------------
    YASMIN LARA
    Technical Marketing Engineer
    JNCIE-SP, JNCIE-ENT, JNCIE-DC, JNCIE-SEC
    JNCDS-DC, JNCIA-DevOps, JNCIP-CLOUD

    Original Message:
    Sent: 08-20-2021 09:11
    From: MIKE WRIGHT
    Subject: Multicast routing PIM L3 switches No PIM interfaces configured

    Hiya

    I studied PIM a while ago and the new company Im working at is using multicast for video streaming.

    The have configured the core switch to be the RP and are then advertising several multicast groups(subnets) and the RP via a routing instance.

    They are using OSPF for the routing between the L3 switches so all switches are aware of the multicast groups and RP.

    I have run show pim interfaces on many of the L3 switches and it say the pim instance does not exist, in other words the switches havent been enabled for PIM

    Some how they are still routing multicast traffic. Would this be because the receives look at their local switch (and has the routes) will route to the RP regardless.

    I would have thought there would be a PIM tree if it is not enabled on any of these switches.

    Thanks

    ------------------------------
    MIKE WRIGHT
    ------------------------------