[AUDIO LOGO]
Finally, let's jump in and get an introduction
to multicast routing protocols.
Our main purpose in this video and this skill, in general,
in regards to routing protocols is really just
to talk about the different choices that are available.
And as we've mentioned in previous videos,
we sort of know that we generally
use PIM, or Protocol-Independent Multicast,
for our multicast routing.
So what we're going to be focusing on here
are some of the other options just
so you're aware that they exist and a little bit
about how they work.
We have a whole nother skill coming up
that focuses in on PIM itself.
So again, this is just an introduction.
Let's go ahead and jump in and get started.
So one of the things we're going to discuss
are the different multicast routing
protocols used in different places of the network.
Not all of the protocols are for between the routers to exchange
multicast information.
So first, we have between the source
and the first-hop router.
And here no protocol is used.
What happens is the sender just starts sending packets
onto the network.
It uses, of course, the correct multicast group
as the destination.
And what happens is that first-hop router
sees the traffic coming in.
And then using its router-to-router protocols,
it then forwards the traffic appropriately.
Now, between those routers, within a single domain,
we have the option to have a couple of different protocols.
But as I mentioned, we generally use PIM.
Some other choices that have been available-- well, we
have what's called Distance Vector Multicast Routing
Protocol, or DVMRP.
This is referenced in RFC 1075, which is a fairly old RFC.
This is based on RIP.
We won't necessarily make any comment
on that, because RIP is a spectacular protocol
to base things on.
And just like RIP, it uses poison reverse
for loop prevention.
I don't think we have to probably say too much about why
this isn't super popular.
Then they decided to do the same thing
by adding multicast to Open Shortest Path First, which,
of course, is OSPF.
And we end up with MOSPF.
This, again, is an older RFC.
It's 1584.
And this just uses standard LSAs to advertise
connected receivers.
This, again, wasn't a very popular choice.
And most devices don't even support this.
Then we have one called Core-Based Tree, or CBT.
This is a little bit newer.
This is from RFC 2189.
This uses the underlying IGP, which
is very similar to PIM itself.
So in a way, it was a bit of a predecessor to PIM.
Now, again, all the ones we've talked about so far
really aren't very popular and/or are not even
supported on most equipment.
Then, of course, we have the most popular,
Protocol-Independent Multicast, or PIM.
So let's talk about some of its details.
First, for loop prevention, it uses
something called the RPF check, or the Reverse Path Forwarding
check.
We'll talk about this in much more detail in our skill
on PIM.
This also uses the underlying IGP--
so for example, EIGRP, OSPF, even RIP.
It'll use whatever your IGP is.
And what it's going to use that for is to do this RPF check
we just talked about.
That's what it's going to use that IGP for.
And it uses that information to build a multicast distribution
tree.
Now, this can operate in either sparse mode or dense mode.
Dense mode is referenced in RFC 3973.
This is referred to as a flood and prune model.
And it's a bit of a push model.
It makes the assumption that everybody wants the multicast.
And those that don't need to prune it back.
Then we have the opposite, which is sparse mode operation.
This one's in RFC 4601.
This one uses a shared distribution tree,
where the multicast packets are delivered to something called
a Rendezvous Point, or an RP.
And then the routers that need this
make a request from the RP for the information.
This is more of a pull model.
So again, PIM is the primary protocol
used for multicast intradomain routing.
And we will have an entire skill coming up on this.
So we understand this in much more detail,
mostly how sparse mode operation works.
Dense mode, again, not an incredibly popular choice.
We'll be focusing mostly on sparse mode.
Now, between domains, we need an interdomain protocol.
For this, we can use multiprotocol BGP,
which we've used for many other things throughout this course.
But understand that this is only used for those RPF checks.
It does not actually build the multicast trees.
This is not part of its job.
So multiprotocol BGP is only going
to be solving half of this problem.
The other part here is Multicast Source Discovery Protocol,
or MSDP.
The job of MSDP is to exchange what's
called Source Active, or SA, messages between the RPs
of different domains.
This way, the RPs know what sources are
available in the other domains.
And once we know where those sources are,
we can then still use traditional PIM sparse mode
within each domain and connect these trees together.
So in this video, we just jumped in with a quick introduction
to some of the multicast routing protocols
that we have available.
Now, keep in mind, out of this whole list,
pretty much the only things we use
these days are, of course, PIM, specifically PIM version 2,
and between domains, multiprotocol BGP with MSDP
along with our PIM version 2.
That's within each of the individual domains.
So that concludes everything we need to discuss in this skill.
And that leaves us with nothing other than to do
a review in the form of a quiz.
And that's exactly what we're going to do next.
Until then, I hope this has been informative for you,
and I'd like to thank you for viewing.