IP Header (version 4)
Byte
Offset
0 1 2 3
IHL (Header
0
Version Type of Service (TOS) Total Length
Length)
IP Flags
4
Identification Fragment Offset
x D M
20
Bytes
8
Time To Live (TTL) Protocol Header Checksum
IHL
12 (Internet
Source Address
Header
Length)
16
Destination Address
20
IP Option (optional, not common)
1 2 3
Bit 0 1 2 3 4 5 6 7 8 9 1 2 3 4 5 6 7 8 9 1 2 3 4 5 6 7 8 9 1
0 0 0
Nibble Byte Word
Version Protocol Fragment Offset
IP Flags
Version of IP Protocol. 4 and IP Protocol ID. Including (but Fragment offset from start of
x D M
6 are valid. This diagram not limited to): IP datagram. Measured in 8
1 ICMP 17 UDP 57 SKIP
represents version 4 byte (2 words, 64 bits) x 0x80 reserved (evil bit)
2 IGMP 47 GRE 88 EIGRP
structure only. increments. If IP datagram is D 0x40 Do Not Fragment
6 TCP 50 ESP 89 OSPF
fragmented, fragment size M 0x20 More Fragments
9 IGRP 51 AH 115 L2TP
(Total Length) must be a follow
Header Length
multiple of 8 bytes.
RFC 791
Number of 32-bit words in
Total Length
Header Checksum
TCP header, minimum value
Please refer to RFC 791 for
Total length of IP datagram,
of 5. Multiply by 4 to get byte
the complete Internet
Checksum of entire IP
or IP fragment if fragmented.
count.
Protocol (IP) Specification.
header
Measured in Bytes.
Copyright 2004 - Matt Baxter - [e-mail]