Internet Protocol version 4 (IP)

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

This page describes IP version 4, which is widely used. There's also an IPv6 protocol page available.

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 independent 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 such as "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

  • Ethernet: IP can use Ethernet and many other protocols. The assigned Ethernet type for IP is 0x800.

  • ICMP: IP uses ICMP for control messages between hosts.

Example traffic

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


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

Preference Settings

  • Decode IPv4 TOS field as DiffServ field: Whether the IPv4 type-of-service field should be decoded as a Differentiated Services field (see RFC2474/RFC2475)

  • Reassemble fragmented IP datagrams: Whether fragmented IP datagrams should be reassembled

  • Show IP summary in protocol tree: Whether the IP summary line should be shown in the protocol tree

  • Validate the IP checksum if possible: Whether to validate the IP checksum

  • Support packet-capture from IP TSO-enabled hardware: Whether to correct for TSO-enabled hardware captures, such as spoofing the IP packet length

  • Enable GeoIP lookups: Whether to look up IP addresses in each GeoIP database we have loaded

  • Interpret Reserved flag as Security flag (RFC 3514): Whether to interpret the originally reserved flag as security flag

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 Wireshark can open gzipped files automatically.

Display Filter

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

Show only IPv4-based traffic (beware: you won't see any ARP packets if you use this filter!):


Show only the IP-based traffic to or from host


Show only the IP-based traffic to or from the subnet (The /24 is CIDR notation for a network address with a mask of 24 one bits, that is, a subnet mask of


Show only the IP-based traffic not to or from host (beware: this is not identical to ip.addr!=


Capture Filter

Capture IPv4-based traffic only:


Capture only the IP-based traffic to or from host


Capture only the IP-based traffic to or from the subnet (The /24 is CIDR notation for a network address with a mask of 24 one bits, that is, a subnet mask of

 ip net 

Capture only the IP-based traffic not to or from host

 not host 

External links


  • RFC894 Transmission of IP Datagrams over Ethernet Networks

  • RFC950 Internet Standard Subnetting Procedure

  • RFC1112 Host Extensions for IP Multicasting

  • RFC1812 Requirements for IP Version 4 Routers === Differentiated Services (replaces Type of Service) ===

  • RFC2474 Definition of the Differentiated Services Field (DS Field) in the IPv4 and IPv6 Headers

  • RFC2475 An Architecture for Differentiated Services


Imported from on 2020-08-11 23:15:08 UTC