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[AUDIO LOGO]

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So now it's time to look
at redundant RPs with BSR.

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Now, just at its
default configuration,

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this actually works the same
as what we saw in auto-RP.

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So we're only going to spend
just a few minutes looking

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at that.

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BSR has two other options
which are really going

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to be the focus of this video.

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The first is we can use priority
to control which RP becomes

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chosen as the active RP.

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This is something that wasn't
really available in auto-RP,

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it just chose the
highest IP address.

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But the other choice
we have with BSR

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is leaving everything
equal, we can actually

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do load sharing per group
between multiple RPs.

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So that's another option we need
to look at because that gives

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us not only redundancy, but
also a certain amount of load

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sharing.

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It's a little more
complicated than it sounds,

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but it gives us load
sharing nonetheless.

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So as usual, let's
bring up our topology

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just real quickly to review
what we're going to do,

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and then we'll jump
into the command line

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and see redundant RPs
with BSR in action.

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So one last time, here we
are on multicast topology 1.

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And there's really
two things that we

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need to discuss before we
jump into the command line.

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The first is, of
course, that we're

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going to be bringing router
4 in here as a second RP.

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But the other thing
we need to discuss

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is when we start
doing load sharing,

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how does BSR actually
do load sharing?

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And the answer to that
is it uses a hash.

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This hash is
referenced in RFC 4601,

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and I put it here just
for your reference.

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Don't panic.

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You don't have to
know this in any way.

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I just wanted to show it to you
so you understand this is not

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as easy as it's just going to do
50/50 load sharing between two

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rendezvous points and so on.

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It uses this
algorithm to combine

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the group, the mask, and the
RP address to create a hash.

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That hash is then used to
load share between the RPs.

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So don't be too surprised when
we start changing the hash mask

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length if you don't exactly
get a nice even load

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share across the RPs.

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That's not exactly
how this works.

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But the other way to
look at it, of course,

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is that any load sharing is
better than no load sharing.

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So all of that said, let's
jump into the command line.

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We'll start on router 4 just
by configuring it to be an RP.

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So this is actually the
exact same configuration

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that we did on router 2,
the only difference is

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we're going to be using router
4's loopback IP address.

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So we'll just paste
this configuration in,

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and now router 4
is a candidate RP.

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So let's go up to the BSR router
5 and see what that looks like.

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So on router 5, we'll do
our show ip pim rp map,

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and what we see is that the BSR
is now aware of both rendezvous

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points.

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These are completely equal,
except for their IP address.

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So the question becomes, which
one is actually being used?

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Well, if we do our
show ip pim rp,

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we can see that for our group,
it's actually using router 4.

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Once again, just
like auto-RP, this

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has chosen the
highest IP address.

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This is why we're not going to
spend a lot of time discussing

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this particular configuration,
because at this point,

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BSR is acting exactly
like auto-RP with only one

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difference.

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If we go to a router
that's not the BSR--

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we've been picking
on router 6 a lot.

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And if we did a show
ip pim rp map here,

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notice that unlike auto-RP where
only the winner gets advertised

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to the other routers, with
BSR, the BSR is really

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just collecting all
of the information

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and sending it out
to the other routers.

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Notice the info
source is the BSR,

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but it's still notifying
us of both RPs.

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That's because in
BSR, each router

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chooses the winner on its own.

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But again, they're all going
to make the same decision

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based on the same criteria.

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So if we do our
show ip pim rp we'll

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see that this is also using
router 4 just like router 5 is.

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Everybody's making
the same decision

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based on the highest IP.

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But what if that's not
what we want to do?

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What if we want to force
router 2 to be the RP

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and not router 4 without
changing their addresses?

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Well, this is where
BSR gives us an option.

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The good news is
this is super simple.

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Notice that both of
these RPs currently

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have a priority of 192.

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Well, the best priority
wins in BSR, however,

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the caveat is the best
priority is actually

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the lowest priority.

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So let's change the priority on
router 2 to make it the winner.

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So on router 2, we'll simply
go into configuration mode.

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Under router pim for IPv4.

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Under the bsr
candidate-rp line, where

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we were advertising 10.2.2.2,
we'll add a priority.

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We can see here the
range is 1 to 255.

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We already saw that
the default was 192.

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So let's just lower
it to say 128.

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Let's commit that change.

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Then let's go back
over to router 6

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and see what's happened.

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So if we just do our
show ip pim rp again,

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we see that now it has switched
to router 2 as we wanted it to.

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And of course, if we
look at the map again,

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we'll see that router 2 has that
lower or better priority of 128

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beating out the 192.

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So what this is doing
is if our goal is

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to have an active
standby type scenario,

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it allows us to choose which
one's going to be active

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and which one's
going to be standby.

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But what if we want
to do load sharing?

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Well in order to do load
sharing, the priorities-- well,

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they're going to have to be
set back to the same again.

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So let's go ahead
and do that first,

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and then we'll
implement load sharing.

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So back over here on
router 2, if we just

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say no on the bsr
candidate-rp command,

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it'll actually take
the whole command out.

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So to set this back,
we're going to have

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to set this back to 192,
which is the default

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and then commit
the change again.

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We can exit out of
configuration here on router 2.

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This time, let's
go over to router 7

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because seeing the load
sharing on router 7, which

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is the last hop router is going
to be a little bit easier.

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So here on router 7, let's
start with our show ip pim rp

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map because we want to see that
they are back to being equal.

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The priorities are
the same, they're

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both 192, which means that
we should be using router 4.

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So if we do our show ip pim rp,
we can see that, yes in fact,

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we are using router 4.

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Now, one other
thing to note here.

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If we're going to do
group-based load sharing

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and we want to
see it work, we're

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going to need more than just
this one group 224.1.1.1.

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So we're going to hop on
to router 8 real quick

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and just have it
join a few groups

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with some various
different group numbers.

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So let's go ahead and do that.

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So here on router
8, I'm just going

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to paste the configuration in.

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I already have it saved.

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You can see here
we're simply joining

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a bunch of different
igmp groups that

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are sort of different in
the first and second octets.

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It doesn't really matter a
whole lot because of the way

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the hash works.

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However, we're having
it join these groups.

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So now if we go over
to router 7 again,

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and we look at our show
ip pim rp, what we see

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is at the moment--

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and you could say
then by default--

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this is not doing any
form of load sharing.

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Everything is going
to the 10.4.4.4.

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The way we control the load
sharing is from the BSR.

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So let's go over to router 5.

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We'll go into
configuration mode.

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And then on the line
where we're configuring

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pim and the
bsr-candidate, again, we

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have to put in the
loopback interface,

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but now we're going to
change the hash mask length.

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Now, the default is
zero, which means

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it's going to put a
zero into the formula,

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and therefore
everything is going

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to become the exact same hash.

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If you're trying to
load share as evenly as

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possible between two
rendezvous points, which

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is a very, very common thing
to do, the best value to use

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here is 31.

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If we hit 31, that allows it
to create 2 different hashes

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to load share between
the rendezvous points

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because there's one
bit that's not masked.

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So if we hit 31 and we go
back over and look at router 7

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again, we look at
our groups again,

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we can see that now we
have a fairly even split.

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We have 3 groups that
are going to router 2,

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and we have 3 groups that
are going to router 4.

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Now, just to show you
what I was talking about,

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let's go change router
5 to something else.

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Let's change router
5 to, say, 16.

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Only mask 16 bits.

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You might think
that that would also

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give you an even load share.

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But like I said, the hash
isn't that predictable.

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Back over to router
7, look at it again.

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And what we see is now we have
4 groups going to router 2

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and only 2 groups
going to router 4.

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So as I mentioned, if you're
in an environment that's

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using two RPs, which
is fairly common,

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the best hash mask length
to use is generally 31.

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Now, you can play around
with other numbers

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and see what kind
of load sharing

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you get or you can sit down
and figure out the hash,

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but generally speaking, 31 works
fairly well if you have 2 RPs.

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So let's go ahead
and set router 5 back

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so we have some nice
even load sharing.

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So again, router 5, we'll
just set it back to the 31.

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We'll go back over to router 7.

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And we can see that we're
back to our nice even load

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sharing of 3 groups going
to 1 RP and 3 groups

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going to the other.

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So this is how we can
do load sharing in BSR.

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So in this video, we took a
look at our redundancy options

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in BSR.

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So the first option, which
we looked at very quickly,

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is we can simply configure
multiple BSR/RP candidates

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and it will simply choose the
one with the highest IP address

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just like auto-RP.

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The second option,
however, gives us

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a little bit more control.

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We can set the best priority,
which is the lowest priority,

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on a particular RP, and then
that will win and become

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the active RP that we're using.

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And of course, the
final choice is

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to change the hash
mask length on the BSR

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itself so that it will
create multiple hashes

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for each different group and
send them to different RPs.

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Again, it can be a
little bit finicky,

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but if you use a 31 with
2 RPs, you generally

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get a fairly even split.

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Now, all of that said,
that covers everything

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that we need to
discuss in this skill,

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which leaves us
with nothing more

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than a review in the form
of a quiz and, of course,

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that's 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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