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[AUDIO LOGO]

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Finally, let's jump in
and get an introduction

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to multicast routing protocols.

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Our main purpose in this video
and this skill, in general,

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in regards to routing
protocols is really just

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to talk about the different
choices that are available.

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And as we've mentioned
in previous videos,

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we sort of know
that we generally

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use PIM, or
Protocol-Independent Multicast,

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for our multicast routing.

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So what we're going
to be focusing on here

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are some of the
other options just

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so you're aware that they
exist and a little bit

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about how they work.

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We have a whole
nother skill coming up

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that focuses in on PIM itself.

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So again, this is
just an introduction.

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Let's go ahead and jump
in and get started.

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So one of the things
we're going to discuss

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are the different
multicast routing

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protocols used in different
places of the network.

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Not all of the protocols are for
between the routers to exchange

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multicast information.

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So first, we have
between the source

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and the first-hop router.

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And here no protocol is used.

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What happens is the sender
just starts sending packets

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onto the network.

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It uses, of course, the
correct multicast group

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as the destination.

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And what happens is
that first-hop router

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sees the traffic coming in.

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And then using its
router-to-router protocols,

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it then forwards the
traffic appropriately.

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Now, between those routers,
within a single domain,

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we have the option to have a
couple of different protocols.

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But as I mentioned,
we generally use PIM.

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Some other choices that have
been available-- well, we

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have what's called Distance
Vector Multicast Routing

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Protocol, or DVMRP.

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This is referenced in RFC 1075,
which is a fairly old RFC.

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This is based on RIP.

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We won't necessarily
make any comment

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on that, because RIP is
a spectacular protocol

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to base things on.

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And just like RIP, it
uses poison reverse

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for loop prevention.

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I don't think we have to
probably say too much about why

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this isn't super popular.

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Then they decided
to do the same thing

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by adding multicast to Open
Shortest Path First, which,

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of course, is OSPF.

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And we end up with MOSPF.

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This, again, is an older RFC.

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It's 1584.

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And this just uses
standard LSAs to advertise

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connected receivers.

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This, again, wasn't a
very popular choice.

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And most devices don't
even support this.

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Then we have one called
Core-Based Tree, or CBT.

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This is a little bit newer.

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This is from RFC 2189.

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This uses the
underlying IGP, which

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is very similar to PIM itself.

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So in a way, it was a bit
of a predecessor to PIM.

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Now, again, all the ones
we've talked about so far

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really aren't very popular
and/or are not even

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supported on most equipment.

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Then, of course, we
have the most popular,

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Protocol-Independent
Multicast, or PIM.

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So let's talk about
some of its details.

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First, for loop
prevention, it uses

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something called the RPF check,
or the Reverse Path Forwarding

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check.

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We'll talk about this in
much more detail in our skill

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on PIM.

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This also uses the
underlying IGP--

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so for example,
EIGRP, OSPF, even RIP.

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It'll use whatever your IGP is.

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And what it's going to use that
for is to do this RPF check

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we just talked about.

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That's what it's going
to use that IGP for.

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And it uses that information to
build a multicast distribution

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tree.

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Now, this can operate in either
sparse mode or dense mode.

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Dense mode is
referenced in RFC 3973.

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This is referred to as
a flood and prune model.

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And it's a bit of a push model.

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It makes the assumption that
everybody wants the multicast.

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And those that don't
need to prune it back.

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Then we have the opposite,
which is sparse mode operation.

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This one's in RFC 4601.

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This one uses a shared
distribution tree,

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where the multicast packets are
delivered to something called

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a Rendezvous Point, or an RP.

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And then the routers
that need this

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make a request from the
RP for the information.

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This is more of a pull model.

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So again, PIM is
the primary protocol

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used for multicast
intradomain routing.

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And we will have an entire
skill coming up on this.

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So we understand this
in much more detail,

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mostly how sparse
mode operation works.

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Dense mode, again, not an
incredibly popular choice.

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We'll be focusing
mostly on sparse mode.

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Now, between domains, we
need an interdomain protocol.

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For this, we can use
multiprotocol BGP,

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which we've used for many other
things throughout this course.

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But understand that this is
only used for those RPF checks.

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It does not actually
build the multicast trees.

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This is not part of its job.

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So multiprotocol
BGP is only going

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to be solving half
of this problem.

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The other part here is Multicast
Source Discovery Protocol,

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or MSDP.

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The job of MSDP is
to exchange what's

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called Source Active, or
SA, messages between the RPs

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of different domains.

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This way, the RPs
know what sources are

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available in the other domains.

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And once we know where
those sources are,

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we can then still use
traditional PIM sparse mode

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within each domain and
connect these trees together.

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So in this video, we just jumped
in with a quick introduction

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to some of the multicast
routing protocols

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that we have available.

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Now, keep in mind, out
of this whole list,

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pretty much the
only things we use

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these days are, of course, PIM,
specifically PIM version 2,

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and between domains,
multiprotocol BGP with MSDP

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along with our PIM version 2.

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That's within each of
the individual domains.

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So that concludes everything we
need to discuss in this skill.

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And that leaves us with
nothing other than to do

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a review in the form of a quiz.

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And that's exactly what
we're going to do next.

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Until then, I hope this has
been informative for you,

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and I'd like to thank
you for viewing.

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