IP Headers

Question 1

Version

Answer 1

Identifies the versio of IP used (4 bits)
IPv4
IPv6

Question 2

IHL (Internet Header Length)

Answer 2

4 bits
Min value = 5 (5 x 4 bytes = 20 bytes with an empty options field)
Max value = 15 (15 x 4 bytes = 60 bytes)

Question 3

Options

Answer 3

variable in length, and necessary to indicate the total length of the header. (0 - 320 bits)
Specifies the length of the header in 4-byte increments.
If the value in this field is 5 then:
5 x 4 bytes = 20 bytes

Question 4

DSCP (Differentiated Services Code Point)

Answer 4

Length: 6 bits
Used for QoS (Quality of Service)
Used to prioritize delay-sensitive data

Question 5

ECN (Explicit Congestion Notification)

Answer 5

Length 2 bits
Provides end-to-end notification of network congestion without dropping packets

Question 6

Total Length

Answer 6

Indicates the total length of the packet (L3 Header + L4 Segment)
Lenght: 16 bits

Question 7

Identification

Answer 7

Length: 16 bits
If a packet is fragmented due to being too large this field will be used to identify which packet the frame belongs to.
All fragments of the same packet will have their own IPv4 header with the same value in this field

Question 8

Flags

Answer 8

Used to control/identify fragments
Bit 0 Reserved, always set to 0
Bit 1 Dont Fragment
Bit 2 More Fragments

Question 9

Fragment Offset

Answer 9

Used to indicate the position of the fragment within the original unfragmented IP packet
Length: 13 bits
Allows fragments to be reassembled in the correct order even if they arrive out of order.

Question 10

TTL (Time to Live)

Answer 10

A router will drop a TTL of 0
Used to prevent infinite loops

Question 11

Protocol

Answer 11

Indicates the protocol
TCP (6) / UDP (17) / ICMP (1) / OSPF (89)

Question 12

Header Checksum

Answer 12

Checks for errors in IPv4 header