Packet Tracer file (PT Version 7.1): https://goo.gl/i8oitv
Get the Packet Tracer course for only $10 by clicking here: https://goo.gl/vikgKN
Get my ICND1 and ICND2 courses for $10 here: https://goo.gl/XR1xm9 (you will get ICND2 as a free bonus when you buy the ICND1 course).
For lots more content, visit http://www.davidbombal.com – learn about GNS3, CCNA, Packet Tracer, Python, Ansible and much, much more.Packet Tracer file (PT Version 7.1): https://goo.gl/i8oitv
Get the Packet Tracer course for only $10 by clicking here: https://goo.gl/vikgKN
Get my ICND1 and ICND2 courses for $10 here: https://goo.gl/XR1xm9 (you will get ICND2 as a free bonus when you buy the ICND1 course).
For lots more content, visit http://www.davidbombal.com – learn about GNS3, CCNA, Packet Tracer, Python, Ansible and much, much more.
Can you answer the questions?
The Address Resolution Protocol (ARP) is a communication protocol used for discovering the link layer address, such as a MAC address, associated with a given network layer address, typically an IPv4 address. This mapping is a critical function in the Internet protocol suite. ARP was defined in 1982 by RFC 826,[1] which is Internet Standard STD 37.
ARP has been implemented with many combinations of network and data link layer technologies, such as IPv4, Chaosnet, DECnet and Xerox PARC Universal Packet (PUP) using IEEE 802 standards, FDDI, X.25, Frame Relay and Asynchronous Transfer Mode (ATM). IPv4 over IEEE 802.3 and IEEE 802.11 is the most common usage.
In Internet Protocol Version 6 (IPv6) networks, the functionality of ARP is provided by the Neighbor Discovery Protocol (NDP).
Translation:
Okay so let’s see if we can answer these questions practically by using packet tracer.
The first thing I’ll do is power cycle the devices to ensure that devices have just booted up. We’ll need to wait until all the links have done green before we can send a ping from PC 1.
Here’s PC 1, I’ll open up a command prompt. IP address of this PC is 10.1.1.1; default gateway is 10.1.1.2.5.4 which should be ISR Router 1.
show ip interface brief
shows us the IP address of the router that’s the IP address of Router 1.
The interfaces in packet tracer have now gone green. So I’ll go to simulation mode, edit the filters and make sure that only ARP and ICMP are enabled.
Back on PC 1, we need to ping PC 2, in other words 10.1.3.2
We can see in packet tracer that an ICMP message is being sent but PC 1 needs to know the MAC address of its default gateway.
So the PC is sending out an ARP request. We can see in the output that the source MAC address is this, destination MAC address is a broadcast, source IP address is PC 1; destination IP address is the router.
Looking at the outbound PDU, information we can see that this is an ARP request message from PC 1 to a broadcast address, source MAC address is this, source IP addresses is this, target IP addresses is this. We don’t know the target MAC address, so based on that, we can already answer some of the questions. I’ll use capture forward to show that the message received by the switch and sent by the switch to the router looks the same.
ARP request message, destination is a broadcast address, source MAC address, source IP address, target MAC address, target IP address.
So to answer some of the questions:
At which points in the network are ARP messages sent?
So we already know that at point A and it will be at point B. Notice the ARP message gets to the router. So the broadcast is received by the router but then the router is going to reply from its MAC address to the MAC address of PC 1.
So source MAC address is the router. We can verify that by looking at the interface on the router
so show interface gigabit 0.0.0
Notice this is the MAC address configured on this interface. I manually configured this MAC address on the router’s interface.
So the ARP message sent back is from the router’s MAC address to PC 1’s MAC address and we can verify PC 1’s MAC address by looking at the PC’s configuration.
Notice the MAC address of PC 1.
So ARP messages are sent at point A and B. The MAC address requested by ARP at point A is the MAC address of the router. We can verify that by going back and looking at the ARP request message sent by the PC.
So on the outbound PDU, we are requesting the MAC address of the route.
So this is the router’s MAC address.
We can see the reply to that by using capture forward and looking at the ARP reply message.
The ARP reply message shows us the MAC address of the router.
So that’s the MAC address that the PC will learn.
We can also answer question 5 which asks:
What is the destination layer 2 address of the ARP request at point A?
So the ARP request message at this point has a destination address of a broadcast.
So question 5 is a broadcast address. So the answer to question 5 is a broadcast address.
What is reply look like?
The reply message has destination address of PC 1…..
