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:
- header and
- 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.