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[AUDIO LOGO]

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So now that we mostly
have IS-IS up and running

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in our environment,
let's take a look

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at a few last little topics.

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First, we'll take a look
at summarization in IS-IS.

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Remember that much
like OSPF, it's

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very limited as to
where we can summarize.

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Then we'll take a quick
look at some filtering.

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And we'll wrap up with
doing some redistribution

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from, well, in this
case, BGP into IS-IS.

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So again, let's take a
quick look at our topology

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just to remember what we're
going to be setting up.

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And then we'll jump
into the command line

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and get these features
up and running.

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So to start off
with, we're going

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to look at router-5's loopback
as it gets advertised over

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towards router-1,
and we're going

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to summarize this on router-2.

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We'll then follow up
with summarizing it

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on router-4 as well because
otherwise, of course,

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the non-summarized route
would come through the bottom

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and get leaked out
through router-3.

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After that, we'll also look
at how to summarize on IOS XE.

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So we'll also summarize
here on router-8

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as routes are being
sent into Area 100.

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So we'll see it
on both platforms.

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Then we'll do a little
bit of filtering.

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We'll filter some of the routes
that are coming from Area 100

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into Area 20.

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And then we'll wrap up with
doing some redistribution

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from BGP into IS-IS
up here on router-6.

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So again, we'll start off
with our summarization.

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Let's jump into the
command line on router-2.

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Actually, before
we jump on router-2

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and do the summarization,
let's first verify

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what the route currently
looks like on router-1.

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So let's do a show IP
route for 10.5.5.5.

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And what we see
here is that we do

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have a slash 32 entry
for this loopback,

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known, of course, via IS-IS-1.

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And this is, in fact,
learned from router-2.

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So now, let's go
over to router-2

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and do our summarization.

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So to do this, we simply go
into the router IS-IS process

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under the address-family.

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And we use the command
summary-prefix.

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After this, it simply
wants the prefix.

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So we're going to summarize
this to a slash 24.

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And then it has a few options.

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We want to summarize this
as it goes into level-2.

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And then if we want,
we can put a tag on it.

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We'll just tag it
as a 2 since it is,

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in fact, coming from router-2.

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Let's go ahead and
commit those changes.

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And let's hop back
over to router-1.

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So if we look at
this same command,

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again, on router-1,
notice that it's now

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showing it as multipathing.

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It's actually going to go
through router-2 and router-3,

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but notice that the routes
aren't actually from router-2.

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Both of these entries
are from router-4.

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So router-2 is no longer
advertising the slash 32.

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If we, instead, ask for the
address of the slash 24,

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now, we see that this is
the summarized route that's

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coming from router-2.

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Now, it can be useful
in certain situations

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to only summarize on one
router on the edge of an area.

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For example, we could
use this to manipulate

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the flow of traffic
going into that area

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by leaking longer prefixes
to one router than the other.

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This is not a very
common thing to do,

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but it certainly could be done.

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Normally, when
we're summarizing,

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the idea is to summarize this
route into the whole rest

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of the network.

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And as such, we
would want to make

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sure we're summarizing the
same on all the routers

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at the edge of that area.

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In our case, that's
routers 2 and 4.

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So let's go ahead and
jump over to router-4

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and do our summarization
there as well.

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So on router-4, again,
it's into router IS-IS-1,

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address-family IPv4.

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We'll set the summary-prefix
to the 10.5.5.0 slash 24

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into level-2.

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And this time, we'll
tag it with a 4.

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Let's go verify on
router-1, again.

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So if we take a
look at this again,

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we can see that whether
we enter the command now

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for the slash 24 or
for the slash 32,

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notice that both of
these are now giving us

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the same route, the slash
24 route, going to router 2,

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which we can also tell
because we see here

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that it also has that tag
of 2 along with the entry.

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Now, if we were to do
a show IP route IS-IS,

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notice that router-8's
loopback is also a slash 32.

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Well, what if we wanted
to summarize on IOS XE?

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Well, let's go over and
take a look at router-8.

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So we'll go into
configuration mode,

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again, into our IS-IS process.

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And it's almost
the same command.

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Instead of summary-prefix,
it's summary-address.

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And another
difference is, notice,

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it first wants the address.

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So we'll again say 10.8.8.0.

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And then it actually wants
the subnet mask written out

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in decimal format.

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So we can't use slash notation
here for our prefix length.

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After that, we have
the same options.

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So we could say that
this, again, is level-2.

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Minor difference here is we have
the dash between level and 2

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rather than a space.

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We can still tag it.

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This is done the exact same way.

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So we could say tag 8.

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And if we want, we can
also set a metric on it.

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So maybe we want
to set a metric.

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We could say metric
100, for example.

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We'll exit out of configuration.

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And now, let's go look at
this route on router-1, again.

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So once again, we'll do
a show IP route IS-IS.

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First, we see that
the 10.8.8.8 is gone,

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and we now have our
slash 24 instead.

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If we look at the
detail on that route,

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first, we see that the
metric is definitely

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above just having a 10
on each interface given

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that it's only a few hops away.

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So the 120 indicates
that it's definitely

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setting that metric to 100.

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Plus, it looks like
two lengths away

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because we haven't really
changed the IS-IS metrics

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on our interfaces at this point.

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And we also see that
it has that tag of 8

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that we set as we
brought the route in.

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Now, something else we could
do along the same lines

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here is we can filter.

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So let's go back
over to router-8.

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Here, we'll just do a
show IP route IS-IS.

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And one thing we
can note is that we

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have a lot of 50 prefixes here.

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We don't need those.

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So let's say we want to
filter them out on router-8.

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All we have to do is go
into configuration mode.

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We'll make an IP prefix list.

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We'll call it something like
PL underscore IS-IS filter.

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And we'll start with a deny of--

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and we'll just deny everything
that starts with a 50.

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So we'll say 50.0.0.0 slash
8, less than or equal to 32.

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So all subnets of it as well.

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Then of course, we have
to allow everything else.

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That will permit
everything else.

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Then we simply go into
our routing process.

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We say, distribute list.

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Notice that we can
actually use access lists

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for this or even a route map,
but we wrote a prefix list.

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So we'll do it
with a prefix list.

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And again, it's PL
underscore IS-IS filter.

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And we want to do
this as the routes are

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coming in to the IS-IS process.

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We'll exit our configuration.

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We'll do a show IP
route IS-IS, again.

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And notice now, all
of the 50 routes

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are gone out of
our routing table.

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So filtering in IS-IS
is just that easy.

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One last thing we
want to look at here

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is redistributing into IS-IS.

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And we'll see that this is just
as easy as the summarization

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and the filtering.

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So let's jump up to
router-6, and we're

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going to do some redistribution
from BGP into IS-IS.

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So on router-6, if we
say show IP route BGP,

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first thing to note is the
only BGP route or prefix

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that we're learning is
router-10's loopback.

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Well, that's fine.

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We don't need a whole lot here.

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What we want to do is simply
go into configuration mode,

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into the IS-IS process.

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All we have to do is say BGP
and then put in the AS number.

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In our demonstration here,
the AS number is 100.

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And note that there's
other options.

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We can, of course, choose
whether we want to redistribute

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just into certain levels.

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We could set the
metrics on these.

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We could, again, go
through a route map

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to manipulate updates
and/or filter.

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So there's a lot of
more advanced options

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here that we'll look
at a little bit more

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in our redistribution skills.

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But for now, we'll just
go ahead and hit Enter

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to do a basic redistribution.

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We'll exit out of configuration.

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And let's go see what this
looks like on another router.

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Let's say, router-7.

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So here on router-7, if we
do a show IP route IS-IS,

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first thing to note is
that we do, in fact, now

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have router-10's loopback.

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It's right here, is a
slash 32, being learned

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as an IS-IS level-2 update.

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But what if we look
at the detail on that?

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Let's do a show
IS-IS rib, and we'll

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ask for that particular prefix.

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The main thing we
want to see here

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is notice on the
prefix attributes.

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The X flag is now set because
this is a redistributed prefix.

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In this video, we took a look at
some little features in IS-IS.

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We started off by looking at
summarization between areas,

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then we took a look at how to
do a little bit of filtering.

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And finally, we
wrapped up with just

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doing a simple
redistribution into IS-IS

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in this example from BGP.

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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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