NETWORK SOLUTION TIPS: Learn Ethical Hacking Basic: Session XXI::Anatomy of TCP/IP Protocols

Anatomy of TCP/IP Protocols

Objectives:

Have a basic knowledge of the Transmission Control Protocol/Internet Protocol (TCP/IP) and their functionality Describe the basic TCP/IP frame structure

Four main protocols form the core of TCP/IP: the Internet Protocol (IP), the Transmission Control Protocol (TCP), the User Datagram Protocol (UDP), and the Internet Control Message Protocol (ICMP). These protocols are essential components that must be supported by every device that communicates on a TCP/IP network. Each serves a distinct purpose and is worthy of further discussion. The four layers of the TCP/IP stack are shown in Figure 2.2. The figure lists the Application, Host-to-host, Internet, and Network Access layers and describes the function of each.

TCP/IP is the foundation of all modern networks. In many ways, you can say that TCP/IP has grown up along with the development of the Internet. Its history can be traced back to standards adopted by the U.S. government’s Department of Defense (DoD) in 1982. Originally, the TCP/IP model was developed as a flexible, fault tolerant set of protocols that were robust enough to avoid failure should one or more nodes go down. After all, the network was designed to these specifications to withstand a nuclear strike, which might destroy key routing nodes. The designers of this original network never envisioned the Internet we use today. Because TCP/IP was designed to work in a trusted environment, many TCP/IP protocols are now considered insecure. As an example, Telnet is designed to mask the password on the user’s screen, as the designers didn’t want shoulder surfers stealing a password; however, the password is sent in clear text on the wire. Little concern was ever given to the fact that an untrustworthy party might have access to the wire and be able to sniff the clear text password. Most networks today run TCP/IPv4. Many security mechanisms in TCP/IPv4 are add-ons to the original protocol suite. As the layers are stacked one atop another, encapsulation takes place. Encapsulation is the technique of layering protocols in which one layer adds a header to the information from the layer above. An example of this can be seen in Figure 2.3. This screenshot from a sniffer program has UDP highlighted.

TIP
A lot of free packet sniffing utilities are available on the Internet. Consider evaluating Packetyzer for Windows or Ethereal for Linux. There are also many commercial sniffing tools, such as Sniffer by Network General. These tools can help you learn more about encapsulation and packet structure.

Let’s take a look at each of the four layers of TCP/IP and discuss some of the security concerns lassociated with each layer and specific protocols. The four layers of TCP/IP include