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Internet Protocol (IP)

The Internet Protocol provides the network layer (layer 3) transport functionality in the InternetProtocolFamily.

The IP protocol is used to transfer packets from one ["IP-address"] to another. The user of this layer will give a packet and a remote IP address, and IP is responsible to transfer the packet to that host.

IP will (hopefully) guide the packet the right way to the remote host. The data transfer is independant of the underlying network hardware (e.g. ["ATM"], ["Ethernet"], or even a SerialLine). If the underlying hardware is not able to transfer the maximum length required (especially on SerialLine's or ["ATM"]), IP will split the data into several smaller IP fragments and reassemble it into a complete one at the receiving host.

When IP wants to send a packet on a LAN, it must first translate the ["IP-address"] given into the underlying hardware address (e.g. an ["Ethernet"] address). IP uses ["ARP"] for this translation, which is done dynamically. On a point-to-point line, this is obviously not necessary, as there's only one host to which a given machine can send a packet.

IP doesn't provide any mechanism to detect PacketLoss, DuplicatePackets and alike.

IP uses ["ICMP"] to transfer control messages to a remote host, like: "Please don't send me more IP packets, I'm full". The famous ping tool also use ["ICMP"].

The typical protocols on top of IP are ["TCP"] and ["UDP"].

Version 4 of the IP protocol is widely used all over the world. As the available ["IP-address"] range is becoming short, version 6 with a much wider address range is becoming more and more popular these days.


The [ RFC791] "INTERNET PROTOCOL" was released in September 1981.

Protocol dependencies

Example traffic

XXX - Add example traffic here (as plain text or Ethereal screenshot).


IP dissector is fully functional. Ethereal provides some advanced features such as IP defragmentation.

Preference Settings

(XXX add links to preference settings affecting how IP is dissected).

Example capture file

XXX - Add a simple example capture file. Keep it short, it's also a good idea to gzip it to make it even smaller, as Ethereal can open gzipped files automatically.

Display Filter

A complete list of IP display filter fields can be found in the [ display filter reference]

Capture Filter


Add more stuff about IPv6 here, or have separate IPv4 and IPv6 pages? -Guy Harris