Network Layer (3) - IP
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Layout of an IP Version 4 (IPV4) packet1 |
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0 |
4 |
8 |
12 |
16 |
20 |
24 |
31 |
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Version |
Header Len |
Diff. Serv |
Total Length incl. Header |
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Identification |
Flags (3 bits) |
Fragment Offset (13 bits) |
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Time to Live |
Protocol |
Header Checksum |
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Source IP Address |
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Destination IP Address |
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Options up to 40 bytes max |
Padding |
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Version is always 4 |
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Header Length * 32 bits, min is 5 (20 bytes) max is 60 |
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Total length max is 65535 octets |
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Protocol is the layer 4 value (e.g., TCP is 6, UDP is 0x11) |
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Checksum is rewritten by every router. See RFC 1071 |
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IPV6 replaces IPV4 specifically with 128 bit addresses |
1Visit http://www.spacerobots.org/dennis/ for a mostly accurate explanation of each field
