In this topology, we have two routers and two PCs.
This is a newly configured topology.
The rioters have just booted up and have no configuration.
So for example, show IP interface brief on router one shows that all interfaces are shut down and no
IP addresses are configured.
What I'll do is no shut interface serial 2/0, the one interface on router one and I'll do something
similar on router two.
Rotor two also has no configuration, so no shut.
Show IP interface brief.
As you can see, the interfaces up up on both sides.
Show interface serial two, slash a zero.
What I'd like to point out is the encapsulation used, which is TLC by default on Cisco routers.
Serial interfaces use Hdl-c as the encapsulation.
So what we could do is go into that interface and give the writer an IP address of, say, ten .1.2.1.
And use a slash 30 mask.
I'll do something similar on router two.
IP Address 10.1 or 2.2.
Ken.
Writer one Ping.
Writer two Yes, it can.
It can write a two ping.
Writer one.
Yes, it can show run interface serial two.
Slash zero.
All we had to do was no, shut the interface.
We didn't have to configure an encapsulation.
We didn't have to configure a clock rate.
You only have to configure clock rate if you're using a back to back cable.
And your rudder is the DC side of the cable here.
Both sides of the dty.
So we didn't have to configure a clock rate.
Let's have a look at tllc frames.
So I'll do a wireshark capture.
On router one's serial interface.
What we can see here.
Is the protocol shown is slop.
But notice we've got HLC and then the Sysco Slope Protocol, which is used for order configuration.
Here we have a CDP message.
So Sysco Hdl-c is the encapsulation used at layer two.
Notice the protocol is referenced as 2000, which is Cisco Discovery Protocol.
And we can see information about the device.
So rather one is a 3725 and is using interface serial to slash zero.
His rather to.
Also using serial interface to slash zero.
If we do a ping.
We should see ICMP.
And there we go.
So, ICMP.
At least to it's once again hdl-c.
So if we look at the actual frame, the encapsulation type is hdl-c.
It's not Ethernet.
So on this one interface, we're using an hdl-c encapsulation.
Notice the protocol reference is the famous x0 x 800, which means IP version for at least three years.
IP version four.
You can see the source IP address and destination IP address in the packet.
The protocol sent is ICMP.
You can see it's an echo.
Here's the echo reply scrolling back to the top.
It's once again hdl-c.
There's the protocol type.
Source IP addresses ten 112 going to ten 1 to 1 and it's an echo reply.
So Cisco Hdl-c or C hdl-c has this protocol field.
Denoting the higher layer protocol.
That's IP version four.
Let's configure IP version six.
So IPV six, address 2001.
Colon, colon one.
Colon colon one.
Slash 64.
En route a to interface serial to slash zero.
IPV six Address 2001.
Colon one.
Colon colon two.
Slash 64.
So ping 2001.
Colon one.
Colon two.
Ping succeeds.
And why shock capture.
We see.
The ICMP messages.
So this is the ping from rata one to rata to notice the protocol type 86 D It's a different protocol
type to IP version for Cisco.
Hdl-c allows you to run multiple higher layer protocols across the same link because of this protocol
field.
So once again, there is IP version six.
And scrolling up here is IP version four and here is CDP, all using different protocol types.
So the layer two encapsulation here is referencing a higher layer protocol.
We would see something similar on an Ethernet frame.
So on router one interface, if zero slash or zero no shut IP address ten 1112452452450
on the PC will give it an IP address of 10.11 2011 with a mosque.
And I'll set the gateway to ten .1.11.
So ping 10.1 and 1.1.
PC can ping rather one.
And if we start to capture on that interface, so we're going to capture traffic on the router.
Notice the frame is ethernet to.
Let's send a ping again.
So there is our ICMP packet.
Notice the protocol type for IP version four is zero 800, which is what we saw.
On the tllc frame.
So here's Hdl-c.
Notice the protocol field.
So when you send packets across a rudder, that shows you quite clearly that the layer two encapsulation
changes, but the high layer protocols are maintained or kept.
Encapsulation used here is Ethernet two.
Encapsulation used here is LC.
Encapsulation here would be Ethernet to once again in this example.
So in order to interface f0/0 no shut IP address.
Ten .1.3.1.
As an example on PC two.
IP address 10.1 3.12.
Put the mask in default gateway.
Paying 10.1 or 3.1.
That works.
Well, enable a writing protocol here quickly to allow the writers to talk to each other.
And this will give us another protocol to capture in Wireshark.
So enable OSPF on all interfaces.
Start a CAPTCHA on this interface.
So we have three Wireshark captures going serial interface, this Ethernet interface and this Ethernet
interface.
PC one should, if OSPF has converged, be able to ping PC two, which it can.
So the pings are succeeding.
Let's have a look at the frame over here on the Ethernet segment.
So there's the frame.
You can see the Ethernet type is Ethernet to.
Source Mac address destination MAC address, which is the router protocol is IP version four.
Just to prove that that's the router.
Show interface if 0/0.
Notice the MAC address is C 201.
3fe80000, which is correct.
So the PC is sending the traffic to the local router using Ethernet too.
In other words, ethernet encapsulation.
At least three.
The source and destination of the two pieces on the TLC capture.
There's the same IP addresses of the PCs at Layer three.
But notice at layer two, the encapsulation is TLC and there are no MAC addresses.
MAC addresses are only used on Ethernet.
They're not used in hdl-c.
Hdl-c lengths are point to point.
There's no need to have MAC addresses.
Anything that you send out of this interface is going to arrive on this interface and vice versa.
Whereas Ethernet allows multiple devices to connect to the same segment, so there's no need to have
MAC addresses.
In Hdl-c it simply references the higher layer protocol and specifies that this is a unicast packet.
What about on the side?
So here's the ping source and destination IP addresses are the same.
Notice, however, that it's Ethernet once again.
So Ethernet too, in this case.
The source Mac address is rather to.
Show.
Interface.
Fast Ethernet.
Zero.
Notice the Mac address.
See?
2023840.
That's the router.
Talking to the PC in this case, PC to the Ethernet type field specifies IP version four as the high
layer protocol.
And here's our IP packet and here's the ICMP information.
So.
The encapsulation changes on every link.
Mac addresses are used on the Ethernet segments.
MAC addresses are not used in hdl-c.