[AUDIO LOGO]
Finally, let's talk about anycast RP.
Fundamentally, this is a fairly simple concept.
We're simply going to have multiple routers with most
likely loopback interfaces sharing the same IP address,
advertise that loopback interface
into our routing protocol, and then we're
going to use that address as the RP.
Now, where the problem comes in is
what happens if a first hop router closest to the source,
registers a source with its closest RP,
and then we have a client make a request on a last hop router,
and when that last hop router joins the star, G tree
and tries to get that source, it ends up on a different RP
because its closest instance is not the same device.
We need some way to synchronize, or you
could say cluster, the source information that's
available on the different RPs, so that if a source gets
registered on one RP, it shares that information with all
of the other RPs that are in the same anycast group,
meaning using that same shared anycast address.
So that's the fundamental idea of what we're
going to be talking about here.
So let's jump in, talk about some
of the more detailed information,
and then we'll wrap up with looking at this on a diagram.
So anycast isn't exactly a way of finding the RP,
but it's a way of running the RP.
So the way this works, again, we're
going to have either two or more.
There's really no limitation on this.
But we're going to have these loopback
interfaces on different RPs that all have the same IP address.
That's the whole idea behind anycast.
We then advertise this address into the IGP,
and the IGP whatever its metric is, so again, maybe this
is cost, maybe this is hop count if you're using RIP, or maybe
EIGRP's bandwidth and delay, but whatever the IGP says,
that's the closest instance we're going to go to.
Then we configure this common IP address
that we've configured on all these devices as the RP
address.
Now, as we mentioned during the introduction,
the problem is going to be if a source is registered with one
RP and then the client tries to get
its information from the last hop router
and the last hop router tries to get to a different RP.
So the RPs are going to have to have exactly the same source
information, or what we call SA, which
is source active information.
Now, there are two ways to do this.
On most Cisco IOS platforms, the choice
is going to be MSDP or Multicast Source Discovery Protocol.
However, on some newer platforms,
such as the Cisco Nexus platform, which
is more focused on the data center,
that allows us to actually use PIM to advertise
the anycast information.
I only bring this up because usually when
a feature gets added to one platform,
it will start going to other platforms.
So even if you don't use Nexus, we
may see this in a future version of IOS.
So PIM has sort of been updated or modified
to carry this information, we just
have to wait for that to catch up with other platforms.
Now, this anycast IP address can be
learned by any of the other means we've already
talked about.
It can be statically configured.
It can, of course, be the RP advertised into auto-RP.
And it can be used in BSR.
In fact, you could have multiple anycast IP addresses being
advertised into BSR, and then BSR
could use its group-based load sharing
to do even more load sharing.
Remember that anycast RP is going
to be doing geographical load sharing.
So this is by itself going to provide redundancy
because, of course, if one RP goes down,
it would simply stop being advertised into the IGP,
and we would go to another instance.
Mobility is sort of the same thing.
We don't really care where this IP address moves
to because it's being advertised in the IGP,
and it might change which is closest to which device,
but overall, it still can be mobile, no problem.
And we're doing geographic load sharing here, of course,
because we're going to the closest instance of the IP
address.
Well, if you take BSR and you add that
to the geographical load sharing,
you're going to get group-based geographical load
sharing, which is a pretty robust option to put these two
types of load sharing together.
So running BSR with anycast RP is actually
a pretty good choice in a lot of environments.
So let's bring up a diagram here and just discuss
a little bit more about how this works
and where we would need MSDP or PIM to synchronize
this information.
So looking at this diagram, we have loopback interfaces
on router 1 and on router 2 that are the same address.
We are configuring all the devices on the network
to use that address as the RP.
But here's where the problem of comes into play.
Let's say this source comes online and begins sending
traffic onto the network.
Well, router 1, being an RP itself,
would register this source on this router, which
means it would immediately create
an S, G entry on this device, and that would be it.
It has no clients, it has nothing on its oil.
This traffic would go nowhere because as of right now,
we don't have any clients.
Now, in order to sort of demonstrate our problem here,
we're going to add some costs to these links.
We're going to say that these cross links
between these devices have a cost of 100.
All of the other links are simply
going to have a cost of 10, just to keep it simple.
So basically, what would happen if the client on the left
were to join this group on router 3,
router 3 would follow the IGP and send a join to router 1
for the shared tree.
Router 1 has the S,G information,
and this would proceed with sparse mode as normal.
This would not be a problem.
Here's where the problem comes in.
Let's say this client on router 4 joins the group.
Router 4 would, of course, send this request to router 2.
It would try to open a star, G to router 2 or a shared tree.
Now, router 2 would do that because it's got a client,
but all it would have is a star, G
entry because router 2 doesn't know where the source is.
What we need is that method of sending this information over
to this RP.
This is that SA message we were talking about,
or the source active message, and this
is what's going to be exchanged with either MSDP
or on some platforms, again, Nexus, PIM.
But this is why we need this additional protocol
to keep the rendezvous points in sync so they all
know about the sources that are available on our network.
So in this video, we took a look at anycast RP, which again,
is not really a way to discover the IP,
it's more of a way to run the IP.
And as we can see on this diagram here,
the overall concept is we have multiple devices
with the same IP address.
That IP address is being advertised
either statically, or through BSR, or through auto-RP.
It really doesn't matter what method
we use to get this address out there to all the other routers,
but that address is configured as the RP.
Now, all the devices can go to the closest instance
of that address.
That's the geographical load sharing.
But as we discussed here, the problem is all of the RPs need
to know about all of the sources then.
And we can do that using either MSDP, or again,
on some platforms.
And may be coming to an IOS-based router near you,
we have a way to do it through PIM on some of those platforms.
So that wraps up everything that we
need to discuss in this skill.
That leaves us with nothing else to do,
except to 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.