RE: Confused about mVPN and MDT

The Customer Multicast is encapsulated inside the Provider Multicast, this
is the MDT. There is the MDT Default and MDT Data groups. PIM and low
bandwidth groups are sent to all PE's using the Default. When a high
bandwidth stream is started, it is moved to a Data MDT and this is signaled
so that PE's that have a CE Joined to the inner group, can join the specific
Data Group. Since all PE's for a given VRF are part of the VRF's MDT Default
Group, and the group must be the same on all PE's, BiDir PIM is a good
choice here. Since specific PE's are joining the MDT Data Groups, and to
make it so that all PE's can be configured the same SSM is a good choice
here. If you use ASM, then each PE must have a distinct Data group range for
the VRF.

David

--
http://dcp.dcptech.com
> -----Original Message-----
> From: nobody_at_groupstudy.com [mailto:nobody_at_groupstudy.com] On
> Behalf Of John Neiberger
> Sent: Tuesday, January 08, 2013 10:48 PM
> To: ccielab_at_groupstudy.com
> Subject: Re: Confused about mVPN and MDT
> 
> Okay, just after sending that I think I read an explanation that makes
> sense and corrects some problems I had. It appears that the PE routers
> participating in the MDT join the MDT group, which is specific to an mVPN.
> That means on the P/PE side of the network, they are signaling to the
> internal RP that they want to join that *,G. When a multicast packet
> arrives on a PE from a CE, that packet gets encapsulated in a GRE packet
> with the MDT group as the destination address. That flows toward the
> provider RP. All of the other participating PEs have joined the MDT group,
> so they receive that multicast packet. Once they receive it, they
> de-encapsulate it and place it onto the vrf with the associated MDT group
> configured on it.
> 
> Is that about right? There are still some parts to this that are
confusing,
> but I think it's starting to make more sense.
> 
> John
> 
> 
> On Tue, Jan 8, 2013 at 8:40 PM, John Neiberger <jneiberger_at_gmail.com>
> wrote:
> 
> > I don't know why, but this seems to be a subject that just doesn't make
> > sense to me. I'm having trouble visualizing the process and I don't yet
> > understand all of the steps necessary to configure mVPN.
> >
> > One thing I'm not entirely sure of is why we would even configure this
in
> > the first place. My only thought is that it is a service to provide to
> > customers and it saves them from having to configure GRE tunnels
> between
> > their sites since regular L3VPN wouldn't support multicast. I don't see
why
> > they couldn't just configure GRE tunnels between their CE routers and
run
> > PIM on them. I guess it would work, but the idea of being a service
> > provider is to offload some of that headache, right?
> >
> > Okay, to the technical stuff. I'll walk through the process as I
> > understand it and you'll see where I'm getting lost. Let's assume that
the
> > basic L3VPN config is done and working.
> >
> > 1. PIM SM is enabled on P/PE routers and an RP is selected.
> > 2. PIM SM is configured in the customer network and will show as a PIM
> > neighbor inside their VRF on our PE router.
> > 3. The MDT address is configured in the VRF.
> > 4. The ipv4 mdt address family is configured in BGP with the same peers
as
> > in the VPNv4 AF.
> >
> > Here's where I get confused. At some point in this process, the PE
routers
> > join the MDT group. They also form GRE tunnels between their loopbacks.
> > This seems to be an automatic process. I don't understand the need for
the
> > MDT group. If the PE routers already have GRE tunnels between them, PIM
> > could run across them with no problem as-is. What function does the MDT
> > perform and what benefit does it provide?
> >
> > Another question is this: what actually triggers the building of those
GRE
> > tunnels? Is that a function of enabling the ipv4 mdt address family?
> >
> > Please un-confuse me. If anyone has any helpful pointers or even old
blog
> > posts, please point the way.
> >
> > Thanks!
> > John
> 
> 
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