IP Header

+--------+--------+-----------------+-----------------------------------+
|  4-bit |  4-bit |     8-bit       |                                   |
| version| header | type of servce  |    16-bit total length (in bytes) |
|        | length |                 |                                   |
+--------+--------+-----------------+-----+-----------------------------+
|                                   |3-bit|                             |
|         16-bit identification     |flags| 13-bit fragment offset      |
|                                   |     |                             |
+-----------------+-----------------+-----+-----------------------------+
|      8-bit      |                 |                                   |
|   time to live  |  8-bit protocol |           16-bit checksum         |
|       TTL       |                 |                                   |
+-----------------+-----------------+-----------------------------------+
|                                                                       |
|                       32-bit source IP address                        |
|                                                                       |
+-----------------------------------------------------------------------+
|                                                                       |
|                    32-bit destination IP address                      |
|                                                                       |
+-----------------------------------------------------------------------+
|                                                                       |
/                          options (if any)                             /
|                                                                       |
+-----------------------------------------------------------------------+
|                                                                       |
|                                                                       |
/                                                                       /
\                                 data                                  \
/                                                                       /
|                                                                       |
|                                                                       |
+-----------------------------------------------------------------------+