Task: Cross
Task number: 090751202111224286060357636905921
1. Content of the task
Task number: 090751202111224286060357636905921
We have the following network (see figure below). On the o1.pl computer, user runs the 'ping dns3.pl' command. The
default DNS server set in computer configuration o1.pl is machine 61.18.76.41. At the begining all computers have an
empty DNS cache. The DNS computer has complete knowledge of the entire system. Simulate the whole communication
process between all computers and routers necessary to handle the generated request. In your solution skip the packets
that will appear on network cards with listed MAC addresses: 00:00:00. In the 59.63.50.0 subnet(s), the ARP tables are
filled in. In the remaining subnet(s), ARP arrays are empty. Consider the protocols: ARP, HTTP, TCP, UDP, ICMP,
DNS. Consider only the first 18 packages. Remark 1: Just because some computer is called e.g.: dns.pl or www.pl does
not mean that you cannot run a browser or dns server on it. Please do not imply names. Remark 2: If there are weights on
the network diagram on the edges, it means that the routing should be done with the paths determined according to these
weights. Remark 3: In the following diagram, the R/S/C symbols indicate Router/Switch/Computer respectively. Remark
4: In the following diagram, the I/M symbols indicate the IP/ MAC address respectively. Remark 5: The MAC address is
shortened to 3 bytes. Remark 6: In task scenarios with TCP protocol, I assumed that the connection is closed by the
client. Remark 7: In task scenarios with ICMP protocol, I assumed that the ICMP protocol is an application layer
protocol, it is because the ICMP packet is generated by the application.
1.
-48 The steps 2, 4, 5, 7 contain the target IP addresses 61.18.76.41, 61.18.76.41, 59.63.50.52, 59.63.50.52
respectively.
2. -52 The steps 1, 5, 6, 8 contain the target MAC addresses 9E:18:47, EF:6A:29, EF:6A:29, 3D:E6:74 respectively.
3. +80 The steps 2, 7 contain the source IP addresses 61.18.76.76, 59.63.50.52 respectively.
4. -52 The steps 1, 2, 3, 5, 6, 7, 8 contain the source MAC addresses 3D:E6:74, 3D:E6:74, 6D:DA:04, 6D:DA:04,
9E:18:47, 3D:E6:74, 5D:E0:D1 respectively.
5. -52 The number of all sent packets in this scenario for the assumed network topology is 10. (without packets from
network cards with addresses indicated in the task content to be removed)
6. -52 The number of all generated packets for the ARP protocol is 4.
7. -48 The number of packets with source or destination IP address equals to 61.18.76.76 is 4.
8. +80 In step 7 the source MAC address is 3D:E6:74.
9. +80 The number of packets carrying incoming application layer protocol data is 3.
10. -48 The number of packets carrying application layer protocol data outgoing from the source is 1.
11. +80 In step 8 the destination IP address is 59.63.50.52.
12. +80 In step 4 the source MAC address is EF:6A:29.
13. -48 The number of packets carrying incoming application layer protocol data is 5.
Computer Networks Department - (C) 2021
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Task: Cross
Task number: 090751202111224286060357636905921
2. Solution of the task
Description of columns in the solution table:
1. Column 'No.' indicates the package number. If there is no entry for a row in the table, it means that the row has been
removed - this was due to the task conditions. It was presented for consistency.
2. 'Prot.' column shows the network protocol used for the current packet - currently supported protocols are HTTP,
ICMP, TCP, UDP, ARP, DNS.
3. Column 'Dir.' indicates the direction of the packet in relation to its source - whether it is the output packet (S->D)
from the output device (computer or router) or the return packet (D->S) - S(Source) D(Destination).
4. Columns 'A>' and 'A<' indicate whether the packet contains an application layer data (request or response
respectively).
5. The 'Ad' column means that the packet should not be included in the solution due to the state of ARP tables in the
given subnet.
6. The 'Nd' column means that a packet should not be included in the solution, due to the task conditions that dictate
that packets appearing on indicated network cards should not be included.
7. The 'Md' column means that the packet should not be included in the solution due to the limited number of packets
in solution for this task.
8. The next 4 columns ('IP send', 'IP recv', 'MAC send', 'MAC recv') mean respectively the sending and receiving IP
and MAC addresses for all packets.
9. The 'Description' column means a short description of the meaning of the package.
Remark 1: The removed packages are presented in the solution table to maintain the consistency. Generally, we do not
consider these packages when answering questions. This does not apply in one case, when you ask about the number of
all the resulting packages - then you should also consider the removed ones.
Remark 2: In case of task scenarios with TCP protocol, I assumed that the client closes the connection.
No.
Prot.
Dir.
ARP
S->D
ARP
D->S
1
DNS
S->D
2
ARP
3
A
>
A
<
A
d
N
d
M
d
IP send.
IP recv.
MAC send.
MAC recv.
Description
+
59.63.50.52
59.63.50.14
3D:E6:74
FF:FF:FF
Who has IP 59.63.50.14, send back your MAC address
+
59.63.50.14
59.63.50.52
9E:18:47
3D:E6:74
MAC for IP address 59.63.50.14 is 9E:18:47
59.63.50.52
61.18.76.41
3D:E6:74
9E:18:47
DNS request for name: dns3.pl
S->D
61.18.76.76
61.18.76.41
EF:6A:29
FF:FF:FF
Who has IP 61.18.76.41, send back your MAC address
ARP
D->S
61.18.76.41
61.18.76.76
6D:DA:04
EF:6A:29
MAC for IP address 61.18.76.41 is 6D:DA:04
4
DNS
S->D
59.63.50.52
61.18.76.41
EF:6A:29
6D:DA:04
DNS request for name: dns3.pl
5
DNS
D->S
+
61.18.76.41
59.63.50.52
6D:DA:04
EF:6A:29
DNS response for name: dns3.pl is 59.63.50.54
6
DNS
D->S
+
61.18.76.41
59.63.50.52
9E:18:47
3D:E6:74
DNS response for name: dns3.pl is 59.63.50.54
ARP
S->D
+
59.63.50.52
59.63.50.54
3D:E6:74
FF:FF:FF
Who has IP 59.63.50.54, send back your MAC address
ARP
D->S
+
59.63.50.54
59.63.50.52
5D:E0:D1
3D:E6:74
MAC for IP address 59.63.50.54 is 5D:E0:D1
7
ICMP
S->D
59.63.50.52
59.63.50.54
3D:E6:74
5D:E0:D1
ICMP ping request
8
ICMP
D->S
59.63.50.54
59.63.50.52
5D:E0:D1
3D:E6:74
ICMP ping response
+
+
+
+
Computer Networks Department - (C) 2021
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