IPv4 Packet Header

The Internet Protocol (IP) uses a Datagram service to transfer packets of data between end systems using routers.

The IPv4 packet header consists of 20 bytes of data. An option exists within the header that allows further optional bytes to be added, but this is not normally used (with the occasional exception of something called "Router Alert"). The full header is shown below:

The header fields are discussed below:

See also

IP Packet Processing

Example Packet Decodes

Operation of an IP Router

Standards Documents:

J.Postel. Internet Protocol, RFC 791

Gorry Fairhurst Date: 18/11/2008 EG3567