Multicast support for MPLS VPNS.

[amms68958]

Hi ,

I am having only entry level knowledge in MPLS and Multicasting..

I have read that multicast across VRFS are currently not supported.

But in the design tips given in the document "Multicast support for MPLS VPNs configuration examples",it is given as follows.

"More than one VRF can belong to the same MVPN multicast domain. IP addressing must be unique within a multicast domain. Leaking of routes and/or packets between multicast domains or into a global multicast routing table is currently not possible."

My qusetions are.

1) more tha one vrf belonging to the same MVPN multicast domain is contradicting the observation that multicast across vrfs are not supported..Can anyone pls give an explanation on this..

Thanks in advance,

Thomas.

[Harold Ritter]

Multicast is indeed supported in a MPLS VPN environment. The VRF being part of how MPLS VPN is deployed therefore needs to support MCAST. What is it precisely that you need to?

For more information about MVPN, please refer to teh following URL:

http://www.cisco.com/warp/public/cc/pd/iosw/prodlit/tcast_wp.htm

Hope this helps,

[maher]

Hi Hritter,

Just want to ask basic question, for multicast mpls vpn, what kind of customers and application if they are using multicast mpls vpn?

On normal implementation mpls vpn is normal sharing files,application server, but for multicast...

thanks in advance,

maher

p/s:still new in multicast :)

[Harold Ritter]

It can be for many purposes. Financial customers mainly use multicast for trading applications. Presentations, training sessions are other examples.

Hope this helps,

[maher]

Hi Hritter,

Thanks for the info. Sorry to "hijeck" the thread. :)

regards,

maher

[q-coelho]

Multicasting is support across an MPLS network unless you have a ATM cell based core using BPX/LSC set-up.

Regards,

Quinton

[robert.hyde]

Thomas,

This is an interesting one. For a better explanation, instead of saying "multicast across vrf's" let's look at "intra-vrf multicast" and "inter-vrf multicast". To define those, take a look at the Network Diagram on the document that you referenced above. Intra-vrf multicast is simply multicast connectivity within the same vrf, between vrf YELLOW on R1 and vrf YELLOW on R5. This works nicely. Multicast is fully functional within one vrf, even if the routers are spread out on the edges of an MPLS network.

Inter-vrf multicast, however, would mean multicast connectivity between multiple vrf's, e.g. vrf YELLOW on R1 and vrf BLUE on R5. This is what they refer to when they say "More than one VRF can belong to the same MVPN multicast domain". And that is true, you can configure it to work. You have to tune vrf import/export so that vrf BLUE can see vrf YELLOW so that the multicast RPF check doesn't fail, but it can work. You would probably want to do some vrf filtering so that YELLOW and BLUE don't completely merge, but I have seen this work.

However, what is not mentioned is what many of us really want to do: Multicast from vrf YELLOW at R1 to both vrf YELLOW on R5 and vrf BLUE on R5 at the same time. This does not work, not as far as anything I have seen/researched or have been able to set up in a lab. This is because the default mdt address has to be unique per router/RSP/device. So once you have gone into "ip vrf YELLOW" on R5 and have configured "mdt default 239.1.1.1", if you then go into "ip vrf BLUE" also on R5 and try to configure "mdt default 239.1.1.1", it will not take the command, and return an error that the default mdt address is overlapping.

And there's the rub: if vrf BLUE on R5 and vrf YELLOW on R5 can't share the same default MDT, they can't share the same multicast tree. Each multicast vrf on the source device can only reach one multicast vrf on the destination device. They do not necessarily have to be the same vrf, but it is still a one-to-one limitation.

We researched and labbed this pretty extensively, but if anyone has any new info I would love to know. Thanks!

[amms68958]

Hi Harold,

Thanks for the url.

Hi Robert,

Thanks for the detailed explanation.

[sandjose]

I have a Query in this region ,If someone could reply i would be thankful

I am using a 3550cat with 12.1 EA image which is used as the PE router . The scenatio i would like to Implment is I have a vrf on which i place the multicast sources .i have a couple of other VRFs within the same PE where i need to receive the Multicast stream on these VRF from the Multicast VRF .But as per Roberts Comments .This wouldn't work since the MDT address cannot be configured on multiple VRFs on the same PE router .

I also face another problem when the image i use doesn't support the MDT address on the VRF . Has anyone implemented this on a 3550 or the image that i need to use for this . Searching through the Cat 3550 doc didn't give me any answers .

I would be thankful if someone can resond to this

-Sandeep

[barisal]

Hi;

As far as i have known, Multicast support for MPLS VPN is announced with 12.2T and 12.2S releases.

Regards,