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Internet Protocol (IP)

In many ways, IP is the network. IP is a connectionless protocol that provides for the delivery of data to logically addressed hosts anywhere on the network | Internet Protocol IP In many ways IP is the network. IP is a connectionless protocol that provides for the delivery of data to logically addressed hosts anywhere on the network. It is important to understand that IP is an unreliable delivery mechanism by design leaving the responsibility of reliable delivery to higher- or lower-layer protocols such as TCP or IEEE 802.2 and 802.3. As far as IP is concerned the data that is transmitted may be delivered lost sent out of order duplicated delayed or otherwise mangled it could not care less what the ultimate result is. When we say that IP is connectionless we mean that each packet that is transmitted is done so independent of every other packet. Consequently packets that are transmitted may take different paths through the network and be lost or delayed whereas other packets are successfully transmitted. Although this concept of best-effort delivery may sound terribly unreliable keep in mind that other protocols are designed that handle reliability thus precluding the need for IP to handle such things. In addition data is generally delivered successfully and true unreliability of data delivery is typically the result of an underlying network or communications failure of which IP would not be able to fix anyway remember each layer operates independent of each other and a failure at the physical layer can only be fixed at the physical layer not the network layer . Note IP is defined by the following RFCs RFC 0791 RFC 2474 RFC 3168 RFC 3260 IP Packet Structure An IP packet sometimes referred to as a datagram has a distinct and defined structure. In simple form an IP packet is the IP packet data which is nothing more than the segment that was passed down from the session layer and the IP packet header as shown in Figure 3-5. Figure 3-5. Simple IP Packet Structure The IP packet header is typically 20 bytes in length unless IP options are used in which case the length may be variable up to a maximum length of 60 bytes and .