Internet Protocol Anatomy Flashcards
IP Row 1 Contents
Version
IHL
TOS
Total Length
Version
Row: 1
Purpose: Defines the version of IP - IPv4/IPv6
Size: 4b
IHL
Row: 1
Purpose: Defines the header length
Meaning: Internet Header Length
Size: 4b
TOS
Row: 1
Purpose: Defines the Type of Service of the packet
Types: Minimize delay, maximize throughput, maximize reliability, minimize monetary cost
Size: 1B
Total Length
Row: 1
Purpose: Defines total length of data gram (including data) or the fragment
Extra: Max value is 65,535 or 0xFFFF
Size: 2 B
Row 2 content
offset: 4-7
Identification, IP flags, Fragment offset
Identification
Row: 2
Purpose: Uniquely identifies each packet.
Extra: Critical for reassembling fragmented pack
Size: 1 B
IP flags
Row: 2
Purpose: Defines whether the packet is fragmented(M) or not (D)
Extra: If this field is manipulated, it can be used to evade IDS and firewall
Size: 3b
Fragment offset
Row: 2
Purpose: Used when packets are fragmented. Defines where the packet should reassemble from the beginning of the IP header.
Size: 13b
Row 3 contents
TTL, Protocol, Header Checksum
TTL
Row: 3
Meaning: Time-to-live
Purpose: Defines how many hops across the internet before the packet expires.
Extra: Varies by the operating system, making it helpful to identify the sender.
Size: 1B
Protocol
Row: 3
Purpose: Defines what protocol is being used with IP. E.g. TCP – 6, ICMP – 1, UDP – 17
Size: 1B
Header checksum
Row: 3
Purpose: Error checking field—calculates the check sum to determine the integrity of the data in the header
Size: 2B
Rows 4 and 5 contents
Row 4: Source address
Row 5: Destination address
Extra: Arguably, the most important part of the header
Row 6 contents
Options: Variable in length and its use is optional.
Padding: Used to fill out the remaining bits and bytes of the header if necessary.
