On Thursday, December 29, 2011 07:32:38 AM Jeff Tantsura wrote:
To my knowledge in most today's networks even if legacy equipment don't support IGMPv3 most likely 1st hop router does static translation and SSM upstream.
Yes, SSM Mapping allows for PIM-SSM to be used in a network where the receivers don't support IGMPv3. But it tends to be static in nature, although both Juniper and Cisco suggest that dynamically-configured options are possible. I couldn't quite decode the Juniper dynamic method, but the Cisco one appears to be based on DNS. That should be interesting (and a colossal screw-up if things are poorly maintained): http://www.cisco.com/en/US/docs/ios/12_3t/12_3t2/feature/guide/gtssmma.html#...
The reason not to migrate to SSM is usually - ASM is already there and works just fine :)
This is our case.
Cost to support RP infrastructure is usually the main non-technical factor to not to use ASM. Would be interested to hear from the SPs on the list.
For us, the cost of the RP isn't an issue. The Sender PE routers (in NG-MVPN speak, the ISP's routers that are connected toward the Source) are also the RP's. But due to the use of NG-MVPN, and how we designed our Multicast backbone, there really isn't any need for the Receiver PE routers to contact the RP whenever a customer is joining a group. BGP has been extended to handle PIM messages in NG-MVPN. When a Source is discovered by the Sender PE router, it generates a Type 5 SA-AD (Source Active, Auto-discovery) BGP update route which is sent to all Receiver PE routers participating in the MVPN. This Type 5 route is generated from the PIM Register state that is created by PIM running between the Sender PE and CE routers. If the Receiver PE router is configured to operate the MVPN in the SPT-only mode, it generates a Type 7 (C-S,C-G) route for every Type 5 route it received, effectively creating the necessary state in the local Receiver PE router. Once customers send (*,G) IGMP reports requesting to join Multicast groups, that state is already present on the Receiver PE router, and traffic starts flowing immediately downstream. If the Receiver PE router is configured to operate the MVPN in RPT-SPT mode, it will follow regular PIM mecahnisms when users are trying to join groups, i.e., Join messages are forwarded toward the RP along the RPT, and then Multicast traffic forwarded along the SPT once the correct (C-S,C-G) state is created locally. The above explanation is somewhat simplified, but represents the general architecture of how things work in NG-MVPN's. For us, SPT-only mode makes sense because we have IPTv probes attached to all Receiver PE routers; and since they're collecting telemetry for all IPTv channels, no point running the RPT-SPT mode. Please note that this whole setup doesn't require MSDP, which is nice! Cheers, Mark.