Draft-Rosen (GRE) mVPN - the need for bgp ipv4 mdt AF?

Hello,

I'd like to clarify my understanding of GRE-based Draft-Rosen concepts. I've been watching relevant ATC (#40) where in the configuration example Brian configured PIM-SM in the SP core network. The last step to tie whole design together was to configure BGP IPv4 MDT Address Family.

This is something I'm confused about. I thought that BGP messages are only needed when running PIM SSM in the core network.
When using PIM ASM, the PE routers know the RP address, so they can register and join particular P multicast group.

In case of SSM it is not possible, so they have to rely on some external mechanism to discover each other. 

Is my understanding correct? 

Comments

  • Yes, you are correct. The MDT AFI is only used with multicast groups operating in SSM mode and that allows you to learn about the PEs participating in that MVPN. If you are using a multicast group address operating in regular sparse mode with an RP, the RP allows the routers to learn about the sources of the default MDT (PEs).

    Cheers,

    Pavel

  • Thank you Pavel for clearing that up for me :)

    Cheers!


  • Technically not required although Cisco recommends getting into the habit of configuring it when PEs have multicast services alongside VPNv4 BGP.



    On 22 Feb 2015, at 11:24, martino <[email protected]> wrote:

    Hello,

    I'd like to clarify my understanding of GRE-based Draft-Rosen concepts. I've been watching relevant ATC (#40) where in the configuration example Brian configured PIM-SM in the SP core network. The last step to tie whole design together was to configure BGP IPv4 MDT Address Family.

    This is something I'm confused about. I thought that BGP messages are only needed when running PIM SSM in the core network.
    When using PIM ASM, the PE routers know the RP address, so they can register and join particular P multicast group.

    In case of SSM it is not possible, so they have to rely on some external mechanism to discover each other. 

    Is my understanding correct? 




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  • That's right.

    Draft-Rosen has 2 versions i.e Draft-Rosen 6 (ASM) & Drat-Rosen 7 (SSM) and they are fairly independent.

    Draft-Rosen 6 (ASM): Uses Shared Tree & RP for auto-discovery of PE's participating in Multicast VPN.

    Draft-ROsen 7 (SSM): PE's sends MDT-SAFI in BGP NLRI's and exchange this capability to discover other PE's participating in MVPN instance.

     



  • Technically not required although Cisco recommends getting into the habit of configuring it when PEs have multicast services alongside VPNv4 BGP.

    Hi Sukhijt,

    If technically it is not required, why Cisco recommends configuring it? It doesn't make much sense for me. 

    Somehow I must have missed that piece of documentation where they recommend it, can you please provide a link?

    Thank you.



  • It's mainly to do with MTI interface not coming unless the MDT family is created in certain older releases, see below:


    Guidelines for Upgrading a Network to Support the MDT SAFI

    We recommended that you configure the MDT SAFI on all routers that participate in the MVPN. Even though the benefits of the MDT SAFI are for SSM tree building, the MDT SAFI must also be configured when using MVPN with the default MDT group for PIM-SM. From the multicast point of view, the MDT SAFI is not required for MVPN to work within a PIM-SM core. However, in certain scenarios, the new address family must be configured in order to create the MTI. Without this notification, the MTI would not be created and MVPN would not function (even with PIM-SM). 

    For backward compatible sessions, extended communities must be enabled on all MDT SAFI peers. In a pure MDT SAFI environment there is no need to configure extended communities explicitly for MVPN. However, extended communities will be needed for VPNv4 interior BGP (iBGP) sessions to relay the route-target. In a hybrid (MDT SAFI and pre-MDT SAFI) environment, extended communities must be configured to send the embedded source in the VPNv4 address and the MDT group address to MDT SAFI neighbors. 





    On 22 Feb 2015, at 20:11, martino <[email protected]> wrote:

    imageSukhjit.Hayre:


    Technically not required although Cisco recommends getting into the habit of configuring it when PEs have multicast services alongside VPNv4 BGP.

    Hi Sukhijt,

    If technically it is not required, why Cisco recommends configuring it? It doesn't make much sense for me. 

    Somehow I must have missed that piece of documentation where they recommend it, can you please provide a link?

    Thank you.




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    http://www.INE.com



    Subscription information may be found at:

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  • Hi Sukhjit,

    Thanks for your reply. It is clear now :)

    Cheers,

     

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