BROCADE IP PRIMER

TCP/IP2The most popular protocol stack to date is TCP/IP. It gained a great deal ofpopularity as more and more people and businesses started using the Internet.The Internet uses TCP/IP as its protocol suite. As a result, manybusinesses have adopted TCP/IP for their internal networks as well.Some might ask what layer TCP/IP resides in. It doesn't, really. TCP/IP is not aspecific protocol. It is a collection of different protocols, extending from Layer 3(Network) to Layer 7 (Application). In this chapter, I will introduce you to the twolayers in the TCP/IP protocol stack that you will want to be most comfortablewith: Layers 3 & 4.Layer 3 TCP/IP: IPAs the title shows, the Layer 3 (Network) protocol in TCP/IP is called InternetProtocol (IP). This is the main protocol, but it is not the only protocol in the TCP/IP Network Layer. As we said in the previous chapter, the Network Layer's job isto decide how the data will get to where it needs to go. I also mentioned that ituses addressing, networks, and routing protocols to accomplish its task. We'regoing to look at each of these in detail in this section.But first, let's take a look at what we're dealing with in Layer 3. This layer wouldhave received the segment from Layer 4 (Transport). IP adds a few bytes of itsown to the front of the segment to make it a packet. These bytes are referredto as the IP header. The header is subdivided this way:HeaderVersionLength4 bits4 bitsToS8 bitsTotalLength16 bitsIdentifier16 bitsFlags3 bitsFrag.Offset13 bitsTimeProtocolTo-Live 8 bits8 bitsHeaderChecksum16 bitsSourceIP Address32 bitsDestinationIP Address32 bitsIPOptionDataVersion. This is a 4-bit number. In most networks, this number will be “4” (or0100, in binary; more on this later). The current version of IP is referred to asIPv4 (or “IP version 4"). A new version, which is already gaining ground, is IPv6.Brocade IP Primer 37