One great way to learn about a technology
is to identify what problems it solve.
So, let's go to the whiteboard and take a look
at a single router with four interfaces with some very
interesting requirements from the customer about what
they want to have happen on that router.
So, let's imagine that they've asked
us to unite to provision a router with these four
interfaces and these four networks.
So, we have the 10.100.0, the 10.12.0, the 10.21.0,
and the 10.201.0 well over 24 it masks.
So, we configure the interfaces, we do know shut. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
So, we configure the interfaces, we do know shut.
It's all great.
We look at the routing table and R1 says,
"Yep, I'm directly connected to these four networks,
and R1 can route between them, no problem."
So, we show up all happy, happy and we say, "Great, it's
all ready to go."
And then the customer says, "Oh, by the way
there's a couple of additional requirements
I forgot to tell you about and here they are."
So, as we draw this topology the customer says, "Well,
actually what's happening is we've got two separate
businesses and one business we're going to have use these
two networks, the 10.100.0 and the 10.12.0.
And we want devices on those two networks WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
And we want devices on those two networks
to build communicate back and forth no problem."
And then behind the scenes, the customer
continues, "We have a second business that we want to run
that is going to use this 10.201 one
network and the 10.21 network.
And we want devices like this PC and this PC and this PC
all to be able to communicate with each other between the two
networks.
But we don't want to have any communication
between these networks up here in blue and the networks
down here."
So, I will draw a red line to say,
"No communication between the network circled in blue WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
"No communication between the network circled in blue
and the network circled in pink down here."
So, as you and I consider that, what can we do?
Well, we could put access control list like everywhere
on the interfaces specifying what's
permitted or not permitted.
But that doesn't scale very well,
those can be really, really ugly.
Is there another option that we can
use to help isolate or segregate those networks,
so there's no communications between the blue networks
and the pink networks?
And the answer is, yes, and that's
exactly where VRF, virtual routing and forwarding WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
exactly where VRF, virtual routing and forwarding
instances can save the day.
And here's how they can help, instead of just using
the single routing table on the router, like we've
seen forever, like we do a show IP route, all the routes that
show up.
That's referred to as the global routing table,
you can get think of it as the default routing table.
So, if we have interfaces that we bring up
those directly connected networks,
those routes for those directly connected networks show up
in the global routing table by default.
But instead of using that global routing table, what we could do
is we could create two separate, I think of them like a mini me WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
is we could create two separate, I think of them like a mini me
version of a routing table.
And these little separate sub routing tables
are referred to as VRFs, virtual routing
and forwarding instances.
When you see VRF, think of a small
and it doesn't have to be small but a sub routing table.
So, if we had this situation where
we need all these routes to build
the routable between each other and these
routes to be routable between each other.
We could create two specific and separate VRFs, virtual routing WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
We could create two specific and separate VRFs, virtual routing
and forwarding instances.
That be one VRF that we could create for the routes that
are here in blue, and we can create a second, another VRF,
a virtual routing and forwarding instance
for the routes here that are in purple.
And the way it works is, once we create these two VRFs,
I put them in color coded to make it easier.
We create the two VRFs and then at the interfaces,
we tell the interfaces, "Hey, you
don't belong to the global routing table,
I want you Mr. Interface to belong to this VRF,"
and we go to 0/1, you belong to this VRF. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
and we go to 0/1, you belong to this VRF.
And then for 0/2 we'd say, "You belong to the purple or pink
or whatever color that is, this VRF.
And 0/3 you belong to this VRF."
And then as a result of that those directly connected
networks on 0/2 and 0/3 would be part of this little VRF routing
table.
And the 0/0 and 0/1 whatever those IP networks
that it's directly connected to, would be
part of this VRF, the blue VRF.
And the cool thing is this interface right here like 0/0,
it can't belong to multiple routing tables.
It can belong to the global routing table by default WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
It can belong to the global routing table by default
or it can belong to we'll call this VRF A up here
or it can belong to VRF B, but it can't belong
to more than one at a time.
So, it's either the global routing table or a VRF
and that's it.
Now, a VRF is a great tool to help
keep a set of routes isolated and in service provider
networks with techniques like MPLS layer 3 VPNs
they're going to use VRFs as part of their solution.
Because they may have like 15 different customers and they're
going to have separate VRFs for each of their customers WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
going to have separate VRFs for each of their customers
as part of their overall solution.
Which leads me to the reason why we
might call something VRF lite.
VRF lite is when we implement virtual routing and forwarding
instances, like we just discussed,
but we're not using it as part of like an MPLS layer 3 VPN
solution.
We're just telling our individual routers
that they've got these new VRFs or associating interfaces
with those VRFs.
And as a result, we're going to have
separate routing tables for each of those VRFs
on a single router.
Another really great way to think about this
is to remind ourselves of how layer 2 switch works. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
is to remind ourselves of how layer 2 switch works.
If we get a layer 2 switch from the factory,
boom put on our desk and power it up.
How many VLANs does it have?
Just one key, VLAN 1, but it's very
likely we're going to carve up multiple VLANs
on that physical switch.
So, you have one physical switch and multiple VLANs,
layer 2 broadcast domains.
But the same logic applies to a router, if we got a router,
boom plugged it in.
How many routing tables do we have for layer 3?
We have one, the global routing table.
But if we wanted two or three separate WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
But if we wanted two or three separate
isolated routing tables like virtual routing tables
on that router.
We simply create three VRFs, virtual routing
and forwarding instances.
Think of a VRF like a little routing table
and then we can have that isolation,
separate routing tables for each of our customers
or each of our businesses or however want
to isolate that layer 3 routing on the router.
And when we do this in a situation we're not involving
MPLS or layer 3 VPNs, they refer to this partitioning
and creating of these small routing tables
on the router as VRF lite. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
on the router as VRF lite.
Think of lite means, we're not using MPLS or layer 3 VPNs,
we're just doing VRFs locally on a router.
All right, so in the next video, I'd
like to share with you the details
of how we would create the VRFs, how we could implement them.
And then we'll proceed to make a design
and then we'll start implementing and verifying
our VRF lite together.
So, 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.