1.) (6 points total) Consider an IP network composed of two networks (13.0.0.0/8
ID: 3640020 • Letter: 1
Question
1.) (6 points total) Consider an IP network composed of two networks (13.0.0.0/8 and 18.0.0.0/8)
connected by a router, R, having interfaces 1 and 2. The IP addresses of hosts A, B, C, and D, as well as
of interfaces R1 and R2, are given in the figure below. Let the Ethernet address of host A be called
MAC_A, of R1 be called MAC_R1, and so forth.
A B 13.0.0.1 18.0.0.1 C D
| | +-----+ | |
--------------------------|1 R 2|--------------------------------------
13.0.0.3 13.0.0.4 +-----+ 18.0.0.7 18.0.0.8
1a) Suppose that host A has some application layer data (layer-5) to send to host B using UDP.
Describe this process in detail. Specifically, explain what happens on host A at each of the five layers of
the Internet Model. Assume for this question that Host A has never sent data before to Host B.
Write your answer in the form of a detailed list, such that step 1 in your list is "(1) Host A's
application passes its data off to the layer-4 UDP module where it is encapsulated and a UDP header is
added." Be sure to include information on how MAC addresses, IP addresses and subnet masks are used
by the host. Include information on the use of ARP and the use of a routing table (if necessary) in your
answer. Your explanation can stop at the point when A's data reaches B's Ethernet interface; you needn't
explain what happens in B's protocol stack.
Explanation / Answer
Host A's application layer data passes to Transport Layer where UDP adds it header and the data is encapsulated in segment.then UDP passes data to network layer which encapsulate segment in a datagram which cantains the ip address of B as the destination address.then network layer passes data to data link layer ,DLL encapsulates datagram and The mac address of B in a frame the passes it to adapter.
Now the question arises how A's DLL will identify the MAC address of B .there is a ARP module which does this task i.e. it returns the mac address of the given ip address.
Initially A and B both are ignorant to each other ,so via routing protocol in network layer there routing tables will store the IP address of each other.
Since A and B belongs to the same network ,and they are ignorant of each other due to absence of information in the routing tables of each other.
Sending node creates a packet called ARP packet which contains the sending and receiveing nodes IP addresses and MAC addresses( ARP query packet is used to determine theLAN address for the corresponding IP address).
Sender passes a frame containg ARP packet to its adapter which broadcast the packet with receiver address given as lan broadcast address.this packet is received by all the host in the network and B will also receive it.B wil match its ip address with the ip address within the packet ,hence respond with the ARP response packet which includes the Its mac address and B's adapter passes it to Lan which will reach to A.and A now knows the MAC address of B.
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