Okay, so let's see if we can answer the questions in this scenario we've been told that PC 1 pings
PC 2 and we need to answer these questions based on the Echo request message sent from PC 1
to PC 2.
So we firstly ask, What is the destination MAC address in the frame at point A in the network when
traffic is sent from one layer to a network across a router the PC is gonna ARP for the routers MAC address
and encapsulate the frame with the routers MAC address when sending traffic to a remote destination?
So the MAC address that will be used is the MAC address of the routers gigabit 000 interface which
is configured as this.
So the answer to the question is E router 1 gigabit
00 MAC address. So I would say for Question 1, the answer is E but let's verify that by using simulation
mode in Packet Tracer, I'm gonna edit my filters to only show ARP and ICMP traffic.
You can click this option show all and then uncheck the various traffic types that you want to view.
On PC 1
I'm gonna send a ping to the IP address of PC 2 and in the output here I'll be able to view the
ICMP traffic, So the inbound PDU shows us that the destination MAC address is the routers MAC address
which is configured as follows.
So again answer to Question 1, is the routers gigabit
000 address is the MAC address used as the destination MAC address in the frame.
And that address is this, so that would be the answer for question 2 which is asking us for the destination
MAC address.
Question 3 asks us what is the encapsulation used.
Notice the encapsulation is Ethernet 2. So Eth 2 is the encapsulation used at point A in the network
we can see that again in the packet tracer capture.
We're then asked to do something similar at point B in the network so I'll click capture forward we could
actually look at that on the frame on the switch and look at the outbound PDU, notice the destination
MAC address is the same, ether type is Ethernet2.
This is the MAC address of the router so the answers here would be very similar.
We're not asked in this example for the encapsulation used but the encapsulation used is ether 2 so
we could look at that here
or we could look at the inbound PDU on the router and you'll notice it has the same information.
So that's the answers to questions
1 to 5. We then need to answer the question, What is the destination MAC address at point C in the
network?
In other words over here, so looking at the outbound PDU what you'll notice is there is no MAC address.
The encapsulation used on the serial interface is HDLC, HDLC doesn't use MAC addresses, MAC addresses
are used in Ethernet so we could see that here or as the inbound PDU on router 2, inbound PDU show
something very similar.
Notice the encapsulation used is HDLC there is no MAC address so the answer to Question 6 is there
is no MAC address at point C in the network and the encapsulation used is HDLC.
We then asked similar information at pointed D in the network.
So what is the destination MAC address.
What is the actual MAC address and what is encapsulation used at point D?
So D is over here so we could look at the routers outbound PDU.
MAC address is this, that is the MAC address of the PC, So IP config shows us the IP address of the
PC, IP config, slash all shows us the destination MAC address of the PC.
So this is the actual MAC address used
going back to our questions.
We need to specify whose MAC address is in the destination frame at point D that is PC 2s MAC address.
This is the actual MAC address and we're back on Ethernet which means it's going to be Ethernet 2
the encapsulation, we can verify that by looking at the outbound PDU on the router notice its Ethernet
2.
So this is gonna be Ethernet 2 once again we could also if we wanted to look at the ingress traffic
on the switch. Ingress shows something very similar destination MAC address frame type is Ethernet 2
that's actually gonna be the same on this link, so on E we could either look at the packet outbound
on the switch notice, it's the same or we could look at the ingress PDU on the PC exactly the
same information is shown for these questions. So if we look at point E the answer to the question will
be the same its PC 2s MAC address, MAC address is that and the frame type is Ethernet 2. So were you
able to answer those questions and can you answer the questions for the return traffic.
In other words the echo reply, so if I click capture forward now notice we're getting an echo reply message.
So if we look at the inbound PDU and we scroll down the type here is this.
But if I go back
the inbound PDU on the PC had a type of 8, so echo request and then the echo reply message over
here
has an ICMP type of this.
And notice you can see that the source MAC address is PC 2 but the destination MAC address is
router 2, so on router 2
show run, notice
this is the MAC address configured on gigabit 000 and that's the MAC address that we see as the destination.
At this point for the Echo reply, source MAC address is this.
Let's work through the process when it gets to the router, the router will see that information on the
inbound PDU destination MAC address is itself.
Source is the PC but on outbound, there are no MAC addresses a different encapsulation is used.
Encapsulation is HDLC but notice the IP address information stays the same.
If we go across the link look at Router 1, inbound PDU is HDLC, outbound PDU is Ethernet 2 destination
MAC address is PC 1 if I look at the config of PC 1 notice that is the MAC address of PC 1 source
MAC address is the router with this MAC address capture forward it'll be the same on the switch, inbound
and outbound PDUs will show that the destination MAC address is
PC 1, source MAC address is the router
same for outbound.
So in and out we'll have that and if we capture forward again we'll see something similar on the
PC for the inbound PDU destination is the PC source is the router. So Packet Tracer allows you to
see the life of a packet quite nicely.
At every stage in the network, it's important that you understand encapsulations source and destination
MAC addresses and how are they used for the CCNA exam. I hope you enjoyed this video.
If you did please like it and please subscribe to my YouTube channel.
I wanna wish you all the very best.