So now it's time to jump in and talk about one
of my favorite multicast topics, SSM
or source specific multicast.
Why is it one of my favorites?
Because it really, really simplifies multicast.
It completely eliminates the need for a rendezvous point.
And if we don't need an RP, that means we don't need static RP.
We don't need auto RP.
We don't need BSR.
Guess what?
We don't have a star comma G tree.
There's no shared tree.
This is why in the previous video,
I said that this is almost the opposite of Bider.
Bider used only shared trees, and SSM doesn't
use shared trees at all.
Everything is a source-based tree.
We have no rendezvous point.
So far less moving parts.
And it's up to the client to tell us where the source is.
Now that's a whole other discussion
that we're not actually going to get into in this course.
How does the client know where the source is?
As a network engineer, that's not directly our problem.
That's something that software developers or application
developers would have to worry about how
the client knows that.
What we need to be aware of is that for the client to tell us
where the source is, they do have
to be running IGMP version 3.
So all of this said, let's jump in this video,
take a look at some of the details of SSM.
And then in the next video, we'll
jump in and implement this, which
is going to be a lot of fun because it
is super simple to implement.
So let's go ahead and jump in, look at those details,
and then we'll move on to our implementation.
So focusing in on some of the details of source specific
multicast or SSM.
Note that this is referenced in RFC 3569.
But this is supposed to use a dedicated group range
of 232.0.0.0/8.
Now note that it actually can use any group you want.
In fact, when we configure it, we're
not going to use the default group
range, just to show how it can be done,
that we can use any group.
However, that said, it is of course recommended
to generally stick with ranges of groups that are dedicated
to a specific purpose.
So real world, of course, I would
recommend using the 232 address range,
but we certainly don't have to.
Now as we mentioned, since there's no rendezvous point,
there's no way for the routers to find where the source is.
It's up to the client to tell us the source
address of the multicast.
Now because of this, it of course
means that we do not need that RP,
and it also means that we don't need something
like MSDP, either between domains
for inter-domain routing, or even between Anycast RPs
because, well, remember the part about not needing any RPs?
Well, if we don't need any RPs, we sure as heck
don't need any cast RPs.
So there wouldn't be any.
Of course, not having an RP means
that there are no shared trees.
There are no star comma G entries.
Everything is an S comma entry, which is already
referenced in our next point.
This is only going to use source-based trees or shortest
path trees.
And we can do this again because the source is known.
We don't need an IP to help us find
the source if the client is telling us where the source is.
And since the source is known, this also
means that again, we can immediately
send that S comma G join message towards the source.
Again, this would be known as the SPT tree.
That's all we're going to have.
Remember the only reason we didn't
do this in normal sparse mode is because we
didn't know the source.
But now we do.
Now as we said, this does require
IGMP version 3 on the client.
If the client does not support that, there is an or here,
we can do SSM mapping.
And we will look at this as our last topic.
But it can either be done statically,
which is what we're going to configure,
or there is a way to tie this to a DNS server.
So it's a little bit beyond the scope
of what we're going to be discussing, but be aware
that it can be done.
So in this video, we discussed some of the details
here about SSM.
Again, key takeaways.
We no longer need a rendezvous point.
Therefore, everything is going to be a source-based tree,
and it leaves the responsibility up
to the client to know where the source is.
And as we said during our introduction,
that's not really something that's
going to generally be the concern of the networking team.
It certainly could be in some environments,
and there are ways that that can be done.
We're actually going to see one in our demonstration
where we're just going to manually configure it.
So there are some ways to do this.
But it's generally not our responsibility.
But again, keep in mind that the clients that
want to do this are going to either need IGMP version
3, which is, of course, the preferred method,
or we can use SSL mappings, and there's actually
another little trick we can do is well,
which really isn't preferred, but I
will show it to you anyway.
So all of that said, it's of course time
to jump into the command line and get SSM up and running.
That's exactly what we get to do next.
Until then, I hope this has been informative for you,
and I'd like to thank you for viewing.