IP Header Structure

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IP (Internet Protocol) has a 20 byte header. Thus each procotol sending data through IP has a control overhead of 20 bytes that is added by IP.

Key Facts

•32-bit number (4 part decimal number)

•Broadcast = host ID set to all 1's Refer to network = host ID all 0's

•Class A: (126 or less) Very large networks, private network = 10.0.0.0

•Class B: (128-191) Medium-sized networks, private network = 172.16.0.0 to 172.31.0.0

•Class C: (192-223) Smaller networks, private network = 192.168.0.0 to 192.168.255.0

Loopback test IP range: 127.0.0.1-127.255.255.254

The IP header fields are explained below in the next section.

[edit section] IP Header

Version: IP version number

IHL (Internet Header Length): Defines length of header information, standard is 5 32-bit words

TOS (Type of Service): priority and congestion details

Total Length: Total length of the datagram (max packet length of 65,535 bytes)

Identification: Use when reassembling of packets is necessart (identify one packet from another)

Flags: Fragmented/Unfragmented frame

Fragmentation Offset: Indicates in units of 8 octets the position of the fragmented data used for reassembly

Time to Live (TTL): Number of hops able to make before packet "dies"

Protocol: Identifies the protocol whose header and data follow the IP header

Header Checksum: Error-checking value at each packet processing point

Source Address: 32-bit IP address of the original transmitting device

Destination Address: 32-bit IP address of the original destination device

Options and Padding: Security, Record Route, Internet Timestamp

Upper-Layer Information: Head/user datagram handed down by upper protocol

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[edit section] Page Credits

Page Conceptualized By: cbrzana