Network Security Questions experienced people on “IP Datagram Packet”.
1. An IP packet has arrived with the first 8 bits as 01000010. What is the version?
a) 3
b) 4
c) 5
d) 6
Answer: b
Clarification: The first 4-bits show the version i.e. 0100 -> version 4.
2. An IP packet has arrived with the first 8 bits as 01000010. What is the header length?
a) 4
b) 8
c) 12
d) 16
Answer: b
Clarification: The right 4-bits multiplied by 4 is the header length (0010=2).
2 x 4 = 8.
3. In an IP packet, the value of HLEN is 1000 in binary. How many bytes of options are being carried by this packet?
a) 16
b) 64
c) 32
d) 8
Answer: c
Clarification: HLEN = 1000 = 8.
8 x 4 = 32 bytes.
4. In an IP packet, the value of HLEN is 5_16 and the value of the total length field is 0028_16. How many bytes of data are being carried by this packet?
a) 10
b) 40
c) 60
d) 20
Answer: d
Clarification: Total number of bytes in the header = 5 x 4 = 20 bytes.
Total length = 0028_16 = 40 bytes.
Data carried by the packet = (40 – 20) = 20 bytes.
5. In an IP packet, the value of HLEN is 516 and the value of the total length field is 002816.What is the efficiency of this datagram?
a) 80%
b) 50%
c) 66%
d) 75%
Answer: b
Clarification: Total number of bytes in the header = 5 x 4 = 20 bytes.
Total length = 0028_16 = 40 bytes.
Data carried by the packet = (40 – 20) = 20 bytes.
Efficiency = payload length / total length = 20/40= 50%.
6. An IP packet has arrived with the first few hexadecimal digits as shown below:
45000028000100000102 . . .
How many hops can this packet travel before being dropped?
a) 2
b) 5
c) 3
d) 1
Answer: d
Clarification: None.
7. An IP packet has arrived with the first few hexadecimal digits as shown below:
45000028000100000102 . . .
The data belong to what upper layer protocol?
a) IGMP
b) UDP
c) OSPF
d) TCP
Answer: a
Clarification: TTL = 01, the packet can travel only one hop.
Protocol field = 02 means IGMP.
8. A packet has arrived in which the offset value is 100. What is the number of the first byte?
a) 400
b) 800
c) 200
d) 780
Answer: b
Clarification: TTL = 01, the packet can travel only one hop.
The number of the first byte is 100 x 8 = 800.
The first byte number is 800.
9. A packet has arrived in which the offset value is 100, the value of HLEN is 5 and the value of the total length field is 100. What is the number of the first byte?
a) 800
b) 880
c) 400
d) 780
Answer: a
Clarification: Total data bytes = total length – header length = 80 bytes in this datagram.
First byte is 800.
10. A packet has arrived in which the offset value is 100, the value of HLEN is 5 and the value of the total length field is 100. What is the number of the last byte
a) 880
b) 879
c) 881
d) 801
Answer: b
Clarification: Total data bytes = total length – header length = 80 bytes in this datagram.
Last byte is therefore 879.