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Securing Protocol Layers   «Prev 
TCP/IP packet construction

IP datagrams

Data transmitted over an internet using IP is carried in messages called IP datagrams. Similar to all network protocol messages, IP uses a specific format for its datagrams. We are looking at IP version 4 and we will examine the IPv4 datagram format, which was defined in RFC 791 along with IPv4.
The IPv4 datagram is conceptually divided into two pieces:
  1. header and
  2. the payload.
The header contains addressing and control fields, while the payload carries the actual data to be sent over the internetwork. Unlike some message formats, IP datagrams do not have a footer following the payload.
Even though IP is a relatively simple, connectionless, unreliable protocol, the IPv4 header carries certain information, which makes it somewhat large.

When you send an email message to someone at rationaldb.com, your email program first transmits this message to a mail server
Datagram Image
Datagram Image
Datagram Image

Datagram Image
Datagram Image
Eventually, the remote computer will receive your email message in the form of a packet, and will then pass the data to the destination server.