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Internet Protocol (IP)

Updated: January 21, 2005

Applies To: Windows Server 2003, Windows Server 2003 R2, Windows Server 2003 with SP1, Windows Server 2003 with SP2

Internet Protocol (IP)

IP is a required TCP/IP standard defined in RFC 791, "Internet Protocol (IP)." IP is a connectionless, unreliable datagram protocol primarily responsible for addressing and routing packets between hosts.

Connectionless means that a session is not established before exchanging data. Unreliable means that delivery is not guaranteed. IP always makes a best-effort attempt to deliver a packet. An IP packet might be lost, delivered out of sequence, duplicated, or delayed. IP does not attempt to recover from these types of errors. The acknowledgment of packets delivered and the recovery of lost packets is the responsibility of a higher-layer protocol, such as TCP.

An IP packet, also known as an IP datagram, consists of an IP header and an IP payload, as shown in the following illustration.

The IP header contains the following fields for addressing and routing:


IP header field Function

Source IP address

The IP address of the original source of the IP datagram.

Destination IP address

The IP address of the final destination of the IP datagram.

Time-to-Live (TTL)

Designates the number of network segments on which the datagram is allowed to travel before being discarded by a router. The TTL is set by the sending host and is used to prevent packets from endlessly circulating on an IP internetwork. When forwarding an IP packet, routers are required to decrease the TTL by at least 1.


  • The Windows Server 2003 family includes the latest version of Internet Protocol (IP), known as IP version 6. For more information, see IP Version 6.

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