Cisco Computer Networking

Chapter 18. Keeping a Watchful Eye Over Who Drives into Your (Network) Neighborhood Chapter 18. Keeping a Watchful Eye Over Who Drives into Your (Network) Neighborhood What You Will Learn After reading this chapter, you should be able to do the following: List some of the ... [full story]

Big Box, Small TruckWhat Do You Do? When you ship something, the shipper can easily handle your package, using the normal trucks, with a single driver stopping by to pick up your package. But the shipper does have a limit to ... [full story]

Summary of Step 1 Although it took about 10 pages of this chapter, the first step in this simple routing example boils down to a pretty basic process, as follows: 1. Create the IP packet by encapsulating transport layer data after an ... [full story]

Figure 9-3. TCP Treats All the Data as Data TCP just needs to worry about the TCP header and doing what it says. In this case, as long as TCP gets the first chunk of data to the server and ... [full story]

Figure 9-5. The Format of the Shipping Label: TCP Headers When TCP adds the header, it has several different fields to use. For error recovery, it uses the sequence number and acknowledgment number fields. The sequence number identifies the segment, ... [full story]

A Leased Line, A Leased Circuit, A Point-to-Point Link, and A WAN Link [View full size image] Before you needed this new WAN link, the telco had thought about supporting lots of customers in Atlanta and Cincinnati. In anticipation of future ... [full story]

A New, Improved, and Faster EthernetLet's Call It Fast Ethernet My mom always used Tide laundry detergent when I was a kid. Every time she bought a new box of detergent, it had a new marketing blurb on it. "New and ... [full story]

A Safe but Potentially Risky Place: The DMZ [View full size image] When using a DMZ, the flows that are allowed are the same as before, but the location of the servers that are accessible from the Internet has changed. The ... [full story]

A Short Trip from Your House (PC) to the Local Store (Server) I sometimes sit back and think about how big and populous the world has gotten. Sometimes I'll drive down a large highway in rush hour, see all the cars, ... [full story]

A Simple Protocol for Error Recovery A couple of changes were made to make this new protocol work. (In the figure, the features added to make the protocol work are noted in bold letters.) First, this protocol requires that the ... [full story]

A Switch for All Speeds LAN switches use logic that relies on information in the Ethernet header. Because all the more advanced forms of Ethernet use the same header, switch forwarding and learning logic do not change based on what speed ... [full story]

Chapter 17. Accepting the Right People and Rejecting the Wrong People What You Will Learn After reading this chapter, you should be able to List the three components of the AAA security model Describe the basic processes used for authentication, authorization, and accounting Explain the ... [full story]

Figure 9-9. Acknowledging Each Byte [View full size image] When the server sends the first segment, it starts with a sequence number of 1. However, the sequence number with TCP actually numbers the bytes, not the segments. So, from TCP's ... [full story]

Chapter 7. Adding Local (Network) Roadways for No Extra Money What You Will Learn After reading this chapter, you should be able to Define the terms LAN, VLAN, and broadcast domain Compare and contrast the concept of a physical LAN and a virtual LAN Explain ... [full story]

Figure 9-2. Adding Shipping Information to Data by Encapsulating in a TCP Header [View full size image] Keith's TCP software, which is typically just a part of the OS, is in charge of delivering the data to the web server. ... [full story]

Routers and WANs: Still a Match Made in Heaven Addressing Is Much More Interesting on Frame Relay Than on Serial Links The last big concept I'll cover for Frame Relay relates to a dilemma that should be familiar because it happens with ... [full story]

Addressing on WAN Serial Links One major difference between Ethernet and HDLC or PPP lies in the address field inside the HDLC and PPP header. There's only one address field, and it's 1 byte long. However, if you sit back and ... [full story]

Allowing the TCP Connection from Figure 18-5 [View full size image] When C3 first sends the IP packet with the initial TCP segment, the firewall notices that the segment has the SYN bit set. The firewall then considers the interface in ... [full story]

An Enterprise Network Connecting to the Internet [View full size image] On the left is an enterprise network, labeled "Internal IP Network" in the figure. In the internal network, there are users at client PCs, like the one labeled C2. C2 ... [full story]

Analog Electrical Signal: Frequency and Amplitude [View full size image] The graph shows that the voltage level on the wire changes continuously over time. Because the voltage changes continuously, the signal is considered to be an analog electrical signal. You might ... [full story]

Appendix B. Converting IP Addresses Between Decimal and Binary Appendix B. Converting IP Addresses Between Decimal and Binary As mentioned in Chapter 10, "Delivering the Goods to the Right Street (IP) Address," IP addresses are 32-bit binary numbers, but they are also frequently written ... [full story]

Part VII: Appendixes   Appendix A: Answers to Chapter Review Questions   Appendix B: Converting IP Addresses Between Decimal and Binary [full story]

Figure 9-1. Application Program and Application Layer Asking the Transport Layer for Help [View full size image] As shown in Figure 8-4 in the previous chapter, the application program includes the user interface and the application layer protocols. In Figure ... [full story]

Are They Coming to Our House or the Neighbor's House? In an Ethernet LAN with a hub, a computer receives a lot of Ethernet frames, but only some of them contain data that is meant for that computer. For instance, Larry ... [full story]

ARP Reply from R1 to Hannah Inside the data portion of the packet, the ARP reply contains the original IP address (8.1.1.250) and the corresponding MAC address (0200.3333.3333). Finally, Hannah knows the Ethernet MAC address that corresponds to the default ... [full story]

Asking for Name Resolution Help Inside the Company When you use directory assistance in the U.S., you pick up the phone and dial 411. To use DNS inside a single company, each TCP/IP host asks for help from a computer that ... [full story]

Asking for Name Resolution Help Outside the Company Your local telephone company has a list of all its customers and their local phone numbers. But there are a lot of people in the world who are not customers of your local ... [full story]

Asking Someone Else to Look Up the Phone Number (IP Address) for You Asking Someone Else to Look Up the Phone Number (IP Address) for You Instead of using your local phone book, you can always call the phone company and ask ... [full story]

Figure 9-4. Assuring Data Delivery In Figure 9-4, Wilma's computer is sending three TCP segments to Fred. The second segment experienced some errors during transmission, and Fred noticed that errors had occurred. How did he know errors had occurred? Well, ... [full story]

Autonegotiation with 10/100 Cards [View full size image] To perform autonegotiation, the switch and the NIC must support multiple speeds, as well as autonegotiation logic. To perform autonegotiation, the switch and NIC send some messages back and forth. These messages simply ... [full story]

Avoiding Catching Cold Computers can get viruses, just like people can. As mentioned earlier, a computer virus is a file, typically a program, which can cause problems after a copy of the virus gets on your computer. The file often gets ... [full story]

Barney and Fred Sending and Receiving at the Same TimeFull Duplex This section started by making an analogy that a hub was like a one-lane road, and that you had to wait until the other car passed before you could ... [full story]