This is the layer 3 (network) component of the TCP/IP protocol.

 IP is a connectionless datagram service.

  NOTE: Routing is performed at this layer!

 IP datagrams are not acknowledged and they can have unique, multicast or broadcast address destinations.

 As datagrams are connectionless, they do not have a fixed route. This powerful concept allows datagrams to be re-routed through other paths thus catering for network failures.

 The IP datagram encapsulates the higher layer protocols and is itself encapsulated in the datalink frame.

 IP sometimes has to split (fragment) datagrams that are larger than the maximum length the medium can handle. This maximum length is referred to as Maximum Transmission Unit (MTU).

 Re-assembly of fragmented datagrams are performed only at the destination even if the segment in middle can handle larger sizes.

 An example:

 This inherent size limitation is invisible to the layers above IP!

 The mechanism for IP addressing is described in detail in another subsection.

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