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[AUDIO LOGO]

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Now that we have our one-way
redistribution done into IS-IS,

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let's move on to OSPF.

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So in this video, we're
going to redistribute

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both EIGRP and IS-IS, as
well as connected into OSPF.

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So let's bring up
our topology design

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where we're going to do this.

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And then we'll jump
into the command line

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and do some
redistribution into OSPF.

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And of course, look at some
of the caveats as we go.

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So what we're going
to configure now

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is we will configure router 1
to redistribute EIGRP into OSPF.

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We'll do the same
thing on router 2.

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Then we'll configure router 1
to redistribute IS-IS into OSPF

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and do the same
thing on router 3.

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And of course, we'll be
looking at these routes

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on various different routers
through our topology.

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So let's jump into
the command line

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and get started with
our redistribution.

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So for this demonstration,
let's start off on router 5

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with simply a show
ip route ospf.

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And all we want
to really look at

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is we just currently have
internal OSPF routes.

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That's all we have on
router 5 right now.

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So let's jump up to router 1
and configure our redistribution

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from EIGRP into OSPF.

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So we'll simply go in
and configuration mode,

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into router OSPF 1,
into our address family.

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And let's do a
redistribute eigrp 100.

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And if we hit question
mark after this,

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we'll see we have some
different choices here.

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We can match on certain
criteria or set the LSA type

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for redistributed routes, do
things like redistribute only

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into NSSA.

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Of course, we can run
our redistribution

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through a route policy that
we could use for filtering

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or route manipulation.

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But what we want to do right
now is just tag these routes.

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And what we're going to do is
we're going to tag them as 90.

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Now, realistically, you
can use any tag you want.

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In a relatively
simple environment,

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I usually use the
tag that's based

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on that routing
protocol's admin distance

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just because it's
easy to remember.

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And then later, we can easily
see that this came from EIGRP.

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Of course, if you want
to use any other tags,

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that's perfectly fine.

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And in a more
complex environment

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where say, for example, we
had more than one EIGRP AS,

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well, we would have
to use different tags,

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or else, we wouldn't
be able to tell

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the difference between them.

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But in a simple environment, I
just find this as an easy way

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to do tags.

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So we'll go ahead
and configure that.

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Commit those changes.

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And we'll exit configuration.

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As far as doing
some verification,

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we can start with a
show ip ospf database.

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We'll filter by external routes.

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And we'll say self to
indicate self-originating.

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These are the external
routes that we are

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putting into the OSPF database.

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We can see here that
we're bringing in say,

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for example, router
9's loopback.

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Here, we have the link
between router 1 and router 9.

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Here, we have the link
between router 2 and router 9.

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And then we have some additional
loopback interfaces on router 9

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that we're also
bringing into OSPF.

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So we can, of course, see these
if we go back over to router 5.

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Let's do our show
ip route ospf again.

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But this time, let's
filter it and say

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to include anything
that's OSPF and external.

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What we see here is
all of those prefixes

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that we just saw
on the database--

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now being brought in as
external type 2's into OSPF.

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This is, of course, exactly
what we're looking for.

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If we were to pick on
one of these prefixes,

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so let's just say, for
example, the 100.9.9.0,

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we can also see that route
tag being applied here--

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the route tag of 90.

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We can, of course, see this
in the database as well.

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And we see here where the
external route tag is set

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to 90 in the database as well.

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Now, let's go ahead and
configure the redistribution

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on router 2 as well.

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Now, we're going to partially
copy and paste this,

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but we're going to
stop here at the tag.

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And the reason is we're going to
go a little further this time.

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And we're going to set the
metric type to be type 1.

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We saw just a moment ago that
the default is to bring routes

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into OSPF as external type 2.

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Well, let's go ahead
and change that,

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bring them in as external
type 1 on router 2

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just to do it a
little different.

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We'll commit our changes
and exit configuration.

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Let's go ahead and look at those
self-generated external LSAs

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again.

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We see that once again, we are
generating all of those LSAs.

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They are, however,
a type 1 this time,

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and they are still being tagged.

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We see it as all
the same entries

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here as we scroll
through the database.

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So now, what should have
happened if we jump back over

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router 5, is router 5 should
now be preferring all the E1's.

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Because remember in OSPF,
external type 1's get chosen

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over external type 2's.

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So we can see that it's now
choosing all the external type

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1's, which are
coming from router 2.

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So now that we have
EIGRP routes in OSPF,

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let's bring in the
IS-IS routes as well.

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So let's go over to router 1.

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Of course, we go back
into OSPF address-family.

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And we'll say to
redistribute IS-IS process 1.

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And we'll go ahead
and tag those as 115,

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which, of course, is IS-IS's
administrative distance.

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We'll commit those changes.

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Exit configuration.

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And we're going to configure the
exact same thing on router 3.

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So we'll just copy and
paste that configuration.

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So here on router 3,
we'll just paste that in.

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And now, let's go
check router 5 again.

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So once again,
we'll look for all

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of the OSPF external routes.

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And notice that we have
considerably more routes now.

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We have all the routes
coming from the IS-IS domain,

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including, for example,
this 88.88.88.0,

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which we know is
coming from router 8.

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So now that we have mutual
redistribution on two routers,

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we know that both
routing domains should

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have routes for each other.

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Now, we can hop over to
router 7 or router 8,

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look at their routing
tables, and make sure

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that they have the OSPF routes.

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But we did do that
in the previous video

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when we redistributed
into IS-IS.

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So that should still be OK.

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Now would be a good time
to test connectivity.

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Let's go ahead and trace
to that 88.88.88.88,

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and we will source that from
our loopback 0 interface.

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As you can see, this
is a routing loop.

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Our traffic is
going to router 2,

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then to router 1,
then to router 7,

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then to router 3, then back
to router 1, back to router 7,

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back to router, and so on.

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So this is entering
a routing loop.

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And this is exactly what we said
can happen if you don't control

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routing loops when you do mutual
redistribution on two routers.

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But let's take a look
at our routing tables

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and figure out why
this is happening.

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The biggest giveaway
is just going

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to be to go look at router 7.

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Let's just start with
that show ip route.

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Just verify that we do still
have all of those routes

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that we're supposed to have.

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We can see that we do.

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However, we do have a
rather large problem.

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If we look at that 88 route.

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Now, what's interesting
is this is showing it

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that it's load-sharing.

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But the fact of the matter is,
it really is not load-sharing.

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It's sending the traffic
back to router 3.

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We saw that in our trace.

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So just so we fully
understand the problem,

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let me bring up
the diagram again.

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So let's remember
what's happening here.

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Router 8 is sending
this update to router 7.

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Router 7 is sending it to router
1 and router 3 through IS-IS.

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Now remember, IS-IS has
an admin distance of 115.

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So then, one of the routers.

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And in this case, just
based on the evidence,

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we can say that it's router 1.

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1 is taking that route and
redistributing it into OSPF.

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Then what happens is OSPF
sends this down to router 3.

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Router 3 now has an admin
distance of 110 versus 115.

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And what it's essentially doing
is replacing the IS-IS route

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in its routing table
with the OSPF route.

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Once that's done, this part
is not happening anymore.

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So now, since router is
configured, of course,

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to redistribute OSPF back into
IS-IS, it's doing just that

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and sending this update
right back to router 7.

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Router 7 now has
two IS-IS routes,

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which, again, theoretically,
it should be load-sharing.

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But we could tell by
the trace, it's not.

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It's sending the traffic
right back to router 3.

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And this is why
we have the loop.

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We'll be solving this
in an upcoming video.

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We're not going to
tackle this right now.

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But that's the problem.

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And that's why we
have this loop.

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In this video, we looked at
how to redistribute routes

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into OSPF.

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A couple of things
to note about that--

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first, all the routes come in by
default as an external type 2,

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which, of course, we can
change on the redistribution,

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like we did on router 2.

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Also, we didn't
exactly point this out

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as we went because
we had discussed it

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earlier in our previous videos.

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However, if you
didn't notice it,

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you can go back
and look that all

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of those routes we redistributed
came in with that default seed

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metric of 20 because
we didn't change that.

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Also, we got our first
look here at a routing loop

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being caused by redistribution.

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And of course, we'll
be solving that later.

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Before we do,
though, we're going

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to configure
redistribution into RIP.

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And that's exactly what
we're going to do next.

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Until then.

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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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