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[AUDIO LOGO]

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The next PIM enhancement
we want to look at

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is Bidir-PIM or
Bidirectional PIM.

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Now, as we've seen
so far through all

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of our multicast
skills, multicast

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is generally a one way tree.

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Everything flows from the
source to all the receivers.

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The problem with
that model is what

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happens when we have a
large number of sources.

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Well, that would
mean we would have

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to have a large number of trees
each one routed at a source.

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And that doesn't scale very well
if we have a lot of sources.

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So the idea behind
Bidirectional PIM

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is we can actually
allow traffic to flow

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up and down the multicast
distribution tree.

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Now, in order to
do that, we do have

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to follow a few guidelines.

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So, in this video, let's try to
talk about what is Bidir-PIM,

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why do we care what's it
for, and how does it work.

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So let's go ahead and
jump in and take a look

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at the attributes of Bidir-PIM.

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So let's talk about
some of those attributes

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of Bidirectional
PIM or Bidir-PIM.

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So as we mentioned
during the introduction,

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PIM is generally
an expanding tree,

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or you could say a one-way
tree from the source going

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to the receivers.

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That's what we've seen so far.

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But as we mentioned,
what if there

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are numerous or many sources?

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Now I put some examples on here
things like video conferencing.

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If we think about this,
everybody on a video conference

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is a source.

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They're also a receiver.

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So again, these can be
sources and receivers.

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That's perfectly fine.

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Another example could be
something like online gaming.

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Everybody has to send their
information from their game

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to everybody else's--

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things like player position
and things like that.

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All of this information
needs to be shared.

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Now, of course, since we
don't support multicast

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on the internet at the
moment, most of these things,

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unless they're internal to
a company such as possibly

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internal video conferencing,
would not be using Bidir-PIM.

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Again, certainly not online
gaming since the online part

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does not support that.

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However, I'm just trying to
give some examples of things

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that could potentially benefit
from Bidirectional PIM.

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Again, the overall
idea is that we

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want to allow the
traffic to flow

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in both directions on the
multicast distribution tree.

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So not only is traffic
flowing down the tree

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but traffic is allowed to
flow up the tree as well.

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Now just based on what
you've learned already,

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hopefully, this is setting
off some alarms in your head

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such as, well, how are
we even going to do that?

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Well, the simple fact is since
there are now multiple sources,

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the source can no longer
be the root of the tree.

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OK, well, that means
we're not going to have

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any more source-based trees.

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Well, if there's no
more source-based trees,

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then what are we going to do?

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Well, quite simply all
the distribution trees

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are now going to be
routed on the RP.

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So the RP is going to
become a central hub

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not just for learning
source information

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but also for the data plane.

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The RP will always
be in the data

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plane in Bidirectional PIM.

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All of our entries are going
to be star comma G entries.

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There are no source trees.

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We only use the shared tree.

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This is critical to how
Bidirectional PIM works.

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For loop prevention
in this environment

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what we're going to
do is we're going

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to elect a designated
forwarder or a DF that's

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in charge of forwarding
all the traffic

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on each individual segment.

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That way, there
are no loops that

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can occur in this environment.

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So, in this video, we just
jumped in and talked about some

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of the attributes of
Bidirectional PIM.

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The big key takeaways
here all traffic

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flows through the
rendezvous point

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that becomes our central
hub, not just for information

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but also for the
data plane and that

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means that all of our trees
are star comma G trees.

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We don't have source trees
because, again, there

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would have to be way
too many of them.

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So talking about
this is very useful,

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but it's also very helpful
to jump into the command line

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and see Bidirectional
PIM in action.

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And that's exactly what
you and I get to do next.

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Till 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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