Tài liệu Internet Protocol (IP) ppt

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.