In this video we're going to take
a look at the concept of virtual links, and why the heck
they're even needed in an OSPF version 3 network.
[MUSIC PLAYING]
And the reason that a virtual link
is needed in OSPF version 3 with IPv6
is the same reason it's needed in OSPF version 2 with IPv4.
And that is, we have a network that doesn't follow the rules.
And we might say, what are the rules?
Well, the rules are with OSPF is that if you
have multiple areas, you need to have a backbone area, area 0. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
have multiple areas, you need to have a backbone area, area 0.
And then any other areas--
like here we have area 1 and area 2--
any other areas have to have at least one ABR.
An ABR is a device, a router, that
has an interface in the backbone area
and an interface in the other non backbone area.
So R3 is an ABR.
R4 is an ABR.
So if we took an additional network,
like let's go ahead and pick on--
let's say R5 has another interface here.
And that interface has an IPv6 address.
And we put that interface and its associated network WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
And we put that interface and its associated network
into area--
let's put it in area 5.
Well, if we put that in area 5, the rule for OSPF
is that every area has to have an area border router.
So R5 is a router connected to area 5.
But R5 is not connected to the backbone.
It's not an ABR.
And as a result, the network, or the networks,
if there's multiple networks in area 5,
they are not going to be seen by the other routers
in the rest of the domain.
So to solve that, we can either put this network here
in area 1. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
in area 1.
Boom.
Problem solved.
Or we can go ahead and connect an area border router
into area 5.
And that way there's an area border router
that's associated with area 5.
Or we could create a virtual link.
And so the way a virtual link would work-- let's go ahead
and put one right back here on R5.
So if this is area 5, what we'd do
is we'd create a virtual link between R5,
who is connected to that non backbone area that currently
doesn't have an ABR, and we'd build a virtual link
between it and an ABR. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
between it and an ABR.
So in this case, R3 is an ABR.
And so what we'd do is we'd have a virtual link between R5
and R3.
And now, R5 would act as an area border router
for the benefit of any other routes and devices that
are sitting in area 5.
Now, one other aspect I want to share with you
is that-- well, actually two.
One is that we don't want to design a network where
we have to use virtual links.
It is a Band-Aid.
So we don't want to do it on purpose,
but it is good for a temporary solution.
And I also want to share with you
one other temporary solution.
And that's this. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
And that's this.
Let's imagine once again that we have R5
and we have a network that it's connected to,
and we put that network into area 5.
So now we have an area 5.
Instead of creating a virtual link, what we could do
is we could create a GRE tunnel.
So we could do a GRE tunnel between R5 and R3.
And we could tell each end of the tunnel on R3,
OK, put that logical network associated with the GRE tunnel,
associate that with area 0.
And then we could tell R5, go ahead
and associate this end of the tunnel, this GRE WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
and associate this end of the tunnel, this GRE
tunnel with area 0.
And now, guess what.
R5 is connected to the backbone.
And without using a virtual link,
R5 is now acting as an ABR on behalf of area 5.
So I wanted to share with you the fact that a GRE tunnel
could be used, and why this might have to be used if we
can't otherwise modify our network is that if area one is
a stub or a not so stubby area, or totally stubbed,
or totally not so stubby, it cannot support being a transit
area for a virtual link.
And in that case, what we could do is we could do a GRE tunnel WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
And in that case, what we could do is we could do a GRE tunnel
and still make our network function
and share the networks in area 5 because we could make R5
an area border router kind of by cheating with that GRE tunnel,
even if we have an otherwise non transit area.
All right.
So having said that, what I'd like to do
is in the next video and lab, I'd
like to give you an opportunity in an IPv6 network
to implement virtual links to kind of get yourself warmed up
to the idea and the syntax.
We'll also get comfortable with some of the show
commands that can help verify it.
And then following the hands on lab to get comfortable, WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
And then following the hands on lab to get comfortable,
then we're going to get uncomfortable,
because in the following two labs
we'll inject some problems.
One of those will be at least a virtual link related problem,
and then we might have one or two other challenges as well
to keep us on our toes.
All right.
So for the warm up, I'll see you in the next video.
Meanwhile, I hope this has been informative for you.
And I'd like to thank you for viewing.