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So now it's time to jump
in and talk about one

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of my favorite
multicast topics, SSM

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or source specific multicast.

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Why is it one of my favorites?

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Because it really, really
simplifies multicast.

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It completely eliminates the
need for a rendezvous point.

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And if we don't need an RP, that
means we don't need static RP.

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We don't need auto RP.

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We don't need BSR.

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Guess what?

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We don't have a
star comma G tree.

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There's no shared tree.

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This is why in the
previous video,

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I said that this is almost
the opposite of Bider.

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Bider used only shared
trees, and SSM doesn't

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use shared trees at all.

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Everything is a
source-based tree.

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We have no rendezvous point.

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So far less moving parts.

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And it's up to the client to
tell us where the source is.

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Now that's a whole
other discussion

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that we're not actually going
to get into in this course.

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How does the client know
where the source is?

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As a network engineer, that's
not directly our problem.

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That's something that software
developers or application

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developers would have
to worry about how

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the client knows that.

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What we need to be aware of is
that for the client to tell us

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where the source
is, they do have

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to be running IGMP version 3.

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So all of this said,
let's jump in this video,

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take a look at some
of the details of SSM.

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And then in the
next video, we'll

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jump in and
implement this, which

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is going to be a lot
of fun because it

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is super simple to implement.

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So let's go ahead and jump
in, look at those details,

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and then we'll move on
to our implementation.

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So focusing in on some of the
details of source specific

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multicast or SSM.

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Note that this is
referenced in RFC 3569.

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But this is supposed to
use a dedicated group range

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of 232.0.0.0/8.

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Now note that it actually
can use any group you want.

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In fact, when we
configure it, we're

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not going to use
the default group

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range, just to show
how it can be done,

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that we can use any group.

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However, that said, it
is of course recommended

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to generally stick with ranges
of groups that are dedicated

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to a specific purpose.

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So real world, of
course, I would

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recommend using the
232 address range,

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but we certainly don't have to.

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Now as we mentioned, since
there's no rendezvous point,

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there's no way for the routers
to find where the source is.

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It's up to the client
to tell us the source

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address of the multicast.

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Now because of
this, it of course

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means that we do
not need that RP,

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and it also means that
we don't need something

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like MSDP, either
between domains

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for inter-domain routing,
or even between Anycast RPs

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because, well, remember the
part about not needing any RPs?

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Well, if we don't need
any RPs, we sure as heck

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don't need any cast RPs.

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So there wouldn't be any.

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Of course, not
having an RP means

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that there are no shared trees.

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There are no star
comma G entries.

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Everything is an S comma
entry, which is already

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referenced in our next point.

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This is only going to use
source-based trees or shortest

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path trees.

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And we can do this again
because the source is known.

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We don't need an
IP to help us find

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the source if the client is
telling us where the source is.

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And since the source
is known, this also

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means that again,
we can immediately

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send that S comma G join
message towards the source.

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Again, this would be
known as the SPT tree.

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That's all we're going to have.

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Remember the only
reason we didn't

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do this in normal sparse
mode is because we

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didn't know the source.

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But now we do.

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Now as we said,
this does require

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IGMP version 3 on the client.

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If the client does not support
that, there is an or here,

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we can do SSM mapping.

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And we will look at
this as our last topic.

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But it can either
be done statically,

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which is what we're
going to configure,

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or there is a way to tie
this to a DNS server.

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So it's a little
bit beyond the scope

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of what we're going to be
discussing, but be aware

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that it can be done.

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So in this video, we
discussed some of the details

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here about SSM.

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Again, key takeaways.

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We no longer need
a rendezvous point.

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Therefore, everything is going
to be a source-based tree,

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and it leaves the
responsibility up

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to the client to know
where the source is.

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And as we said during
our introduction,

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that's not really
something that's

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going to generally be the
concern of the networking team.

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It certainly could be
in some environments,

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and there are ways
that that can be done.

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We're actually going to see
one in our demonstration

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where we're just going
to manually configure it.

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So there are some
ways to do this.

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But it's generally not
our responsibility.

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But again, keep in mind
that the clients that

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want to do this are going
to either need IGMP version

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3, which is, of course,
the preferred method,

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or we can use SSL mappings,
and there's actually

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another little trick
we can do is well,

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which really isn't
preferred, but I

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will show it to you anyway.

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So all of that said,
it's of course time

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to jump into the command line
and get SSM up and running.

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That's exactly what
we get 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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