[AUDIO LOGO]
So we've already mentioned the fact
that IS-IS actually runs on top of CLNS,
and we mentioned in the previous video
that that means we have to design our CLNS addressing.
Well, that's what we're going to take a look at in this video.
How is that address formatted?
How do we put it on the router?
And ultimately, how do we design it for our environment?
So let's go ahead and jump in, take a look
at some of the details.
We'll jump on to the command line
and see how this is configured on the routers.
And then just for fun, we'll even jump into Wireshark
and see what this actually looks like on the wire itself.
So let's go ahead and get started.
So first, let's talk about the overall IS-IS
addressing format, and then we'll
talk about how Cisco uses this.
So this is an example of what the headers look like.
Let's go over these one by one.
So the first thing to note here is
that the ISO NSAP addresses actually
consist of two elements.
The first is the Initial Domain Part or the IDP.
We can see on the diagram--
that would be this part right here--
this is then divided into two other parts.
The Authority and Format Identifier, AFI, this
specifies the format of the address and the authority
it's assigned to.
Then you have the Initial Domain Identifier or the IDI.
This is the subdomain under the AFI.
So that would, of course, be these two fields
up here, the AFI and the IDI.
Next up, is the Domain-Specific Part, or the DSP,
and that's, of course, this part of the addressing over here.
Now, as we can see, the DSP is broken up into three parts.
The first is the high-order DSP.
This is what subdivides the domain into areas.
Then we have the system ID.
The system ID is sort of like the OSPF router ID.
This is a unique identifier for each device in the area.
And then finally, we have the NSEL,
which is sort of like an IP port number.
This is generally going to be 00 when we're configuring the net
number.
Look at it like when you're putting an IP
address on an interface.
You don't put a port number on it,
you just put on the address.
So the NSEL, acting like the port number,
we would use this in part of the address for a specific process,
such as IS-IS.
And we'll see this when we get to our Wireshark packet
captures, where this NSEL is not 00, it's set to another number.
If it's 00, it's referring to the device itself or the net
number.
Now, the way Cisco has chosen to implement all of this
is we usually set the AFI to 49.
This simply means that it's locally administered
addresses--
in a way, sort of like RFC1918 addresses
that we have in IP version 4.
This would then be followed by the area ID, which, of course,
we have to make the same on all the devices in the area.
Next, we have the system ID, which
would be the next 6 bytes.
This, as we said, is a unique identifier for the device.
And then the NSEL, again, set to 00 to indicate the device
itself.
That's what we're going to be configuring.
An example of this would look something
along these lines, where this portion of the number
is that AFI.
This portion of the number is the area.
This is the system ID.
And the last section here is that NSEL.
But this is an example of what a net number that we put into one
of our devices might look like.
Now, technically you could use the same system ID
on devices in different areas.
But as we're saying here at the bottom,
this is generally not recommended, OK?
Best practice is to make sure that all of the system IDs
are unique in the entire domain.
Again, every net number has to be unique.
But I could theoretically, if the area number is different,
I could reuse system IDs.
And we're simply saying that's generally not recommended.
I wouldn't do that.
Keep all of your system IDs unique.
This is only one number we have to come up
with for each device.
So let's jump into the command line here real quick,
take a look at what this looks like when we're configuring it
on the device.
So we just have a real simple topology here,
and we're just going to be taking
a quick look at router 1.
I just wanted to show you the topology so you
can see that it does, in fact, have devices
that it's talking to out its different interfaces.
So we're going to look first at the configuration on router 1.
And then we're going to fire up Wireshark and we'll take a look
at a packet capture here on the G0/0/0/0 interface.
And we'll look at an IS-IS hello that's
headed over towards router 2.
So let's start by jumping into the command line.
So here on router 1, let's just do a show run.
We'll begin with IS-IS and we can see right here
an example of the net number.
So you can see how we're leading with that 49
for the private addressing, and then this portion
is specifying the area.
So this is putting router 1 into area 1,
and then this portion is the system ID.
So what this net number is doing is
it's making router 1 system ID 1 in area 1.
And as you can see here, that NSEL cell number is 00
because we're not going to be specifying a port here
for anything.
So let's also do a show isis prot,
and here we can actually see how that's broken up.
We can see where the system ID is 1,
and we can see where the area is also set to 1.
So we can see in this output how it sort of breaks it up
into the two different parts.
Now, this may be just a little bit confusing
just because both the system ID and the area
are both 1 on this router.
Let's just take a look at the same thing on router 4
real quick.
On router 4, we'll also do the show isis prot.
This is a little easier to see, where the system ID is now 4
but it's still in area 1.
And as we mentioned, let's take a look at this in Wireshark
as well.
So here's our Wireshark capture.
Again, this is G0/0/0/0 on router 1,
and what we can see here is that we've actually exchanged hellos
between system ID 1 and system ID 2.
So we've gotten a hello going both ways.
So rather than looking at router 1's hello, which again might
be a little bit confusing, let's take a look
at the one coming from router 2.
If we look at the one coming from router 2,
we can open up the ISIS HELLO, and we
see that this is coming from the system ID of all zeros
and then a 2.
Also, we have area addresses down here.
If we open up area addresses, scroll down a little bit,
we also see the area address here listed
as the all zeros and the 1.
Now, as you can see, the 49 is technically listed here
as part of the area address.
But again, we generally discard that because it's just used
for the private addressing.
So we would just refer to this as area 1.
So we can see this information being exchanged in the hellos
where each device is sending their system IDs and the area
that they belong in.
In this video, we jumped in and we took a look
at our CLNS addressing.
We saw how the different parts are broken up,
and then we saw how to enter this information on the Cisco
CLI.
We also, of course, took a look here at Wireshark,
and we can see that this information is being
exchanged in the IS-IS hellos.
I hope this has been informative for you
and I'd like to thank you for viewing.