Open the file LSG01-PTSkills4.pka on the CD-ROM that accompanies this book to perform this exer- cise using Packet Tracer.
Upon completion of this activity, you will be able to do the following:
■ Configure hosts and services.
■ Connect and configure hosts and services on the model of the lab network. ■ Explore How DNS, UDP, HTTP, and UDP work together.
■ Use simulation mode to visualize the operation of DNS, UDP, HTTP, and TCP on the model of
the lab network.
Background
Throughout the course, you will be using a standard lab setup created from actual PCs, servers, routers, and switches to learn networking concepts. At the end of each chapter, you will build increas- ingly larger parts of this topology in Packet Tracer, and analyze increasingly more complex protocol interactions.
You will use the topology in Figure 4-21 and the addressing table in Table 4-18 to document your design.
Packet Tracer
Companion
Packet Tracer
Figure 4-21 Topology for Challenge
Table 4-18 Addressing Table
Device Interface IP Address Subnet Mask Default Gateway
R1-ISP Fa0/0 192.168.254.253 255.255.255.0 N/A S0/0/0 10.10.10.6 255.255.255.252 N/A R2-Central Fa0/0 172.16.255.254 255.255.0.0 10.10.10.6 S0/0/0 10.10.10.5 255.255.255.252 10.10.10.6 S1-Central VLAN 1 172.16.254.1 255.255.0.0 172.16.255.254 PC 1A NIC 172.16.1.1 255.255.0.0 172.16.255.254 PC 1B NIC 172.16.1.2 255.255.0.0 172.16.255.254 Eagle Server NIC 192.168.254.254 255.255.255.0 192.168.254.253
Task 1: Repair and Test the Topology
The server has been replaced. It must be powered on. Then configure it with the following settings:
■ IP address 192.168.254.254 ■ Subnet mask 255.255.255.0 ■ Default gateway 192.168.254.253
■ DNS enabled, with the association of eagle-server.example.com with the server’s IP address ■ HTTP enabled 1841 R1-ISP 1841 R2-Central PC 1A PC 1B 2960-24TT S1-Central Server-PT Eagle_Server
Connect the Eagle Server to the Fa0/0 port on the R1-ISP router using a crossover cable. PC 1A has lost its IP address information. Configure it with the following settings:
■ IP address 172.16.1.1 ■ Subnet mask 255.255.0.0 ■ Default gateway 172.16.255.254 ■ DNS server 192.168.254.254
Connect PC 1A to the Fa0/1 port of the S1-Central switch using a straight-through cable. Verify your work using feedback from the Check Results button and the Assessment Items tab. Test connectivity, in real time, by using the Add Simple PDU to test connectivity between PC 1A and the Eagle Server. Note that when you add a simple PDU, it appears in the PDU List window as part of Scenario 0. The first time you issue this one-shot ping message, it will show as Failed; this is because of the Address Resolution Protocol (ARP) process, which is explained later in Chapter 9, “Ethernet.” Double-clicking the Fire button in the PDU List window, send this single test ping a second time. This time it will suc- ceed. In Packet Tracer, the term scenario means a specific configuration of one or more test packets. You can create different test packet scenarios by using the New button (for example, Scenario 0 might have one test packet from PC 1A to Eagle Server, Scenario 1 might have test packets between PC 1B and the routers). You can remove all test packets in a particular scenario by using the Delete button. For example, if you use the Delete button for Scenario 0, the test packet you just created between PC 1A and Eagle Server will be removed; please do this before the next task.
Task 2: Explore How DNS, UDP, HTTP, and TCP Work
Together
Switch from real time to simulation mode. Make sure Event Filter is set to display DNS, UDP, HTTP, TCP, and ICMP. Open a web browser from the desktop of 1A. Type the URL eagle-
server.example.com, press Enter, and then use the Capture / Forward button in the event List to
capture the interaction of DNS, UDP, HTTP, and TCP.
You can examine the packet in two ways: by clicking the packet envelope as it is displayed in the ani- mation, or by clicking the Info column for that packet instance as it is listed in the Event List. Play this animation and examine the packet contents (PDU Information window, Inbound PDU Details, Outbound PDU Details) for each event in the event list, especially when the packets are at PC 1A or at the Eagle Server. If you receive a Buffer Full message, click the View Previous Events button. Although the processing of the packets at the switch and the routers might not make sense to you yet, you should be able to see how DNS, UDP, HTTP, and TCP work together by studying tracing the packets and using the PDU Information window to look “inside” them.
Task 3: Reflection
Can you make a diagram of the sequence of protocol events involved in requesting a web page using a URL? Where might things go wrong? Compare and contrast DNS and HTTP, and UDP and TCP.
The Study Guide portion of this chapter uses a combination of matching, fill-in-the-blank, multiple-choice, and open-ended questions to test your knowledge of the importance of data networks and the major components and characteristics of network architectures.
The Labs and Activities portion of this chapter includes all the online curriculum activities and labs to ensure you have mastered the practical, hands-on skills needed to understand the opportunities and challenges associ- ated with modern networks.
As you work through this chapter, use Chapter 5 in the Network Fundamentals CCNA Exploration online cur- riculum or use the corresponding Chapter 5 in the Network Fundamentals CCNA Exploration Companion
Guide for assistance.
Study Guide
IPv4
The network layer provides services to exchange the individual pieces of data over the network between end devices.
The most significant network layer protocol is the Internet Protocol (IP). IP version 4 (IPv4) is the network layer protocol used as an example throughout this study guide. IPv4 defines many different fields in the packet header. These fields contain binary values that the IPv4 services reference as they forward packets across the network.
Concept Questions
1. What are the four basic processes used in the network layer to accomplish end-to-end transport?
To accomplish end-to-end transport, Layer 3 uses the following four basic processes: 1. The network layer must provide a unique address for these end devices.
2. The data must be packaged so that it can be sent in a manageable size.
3. The network layer must provide services to direct these packets to their destination host. 4. The packet arrives at the destination host and is processed at Layer 3.
2. List three protocols implemented at the network layer that carry user data.
Answers will vary but could include Internet Protocol version 4 (IPv4), Internet Protocol version 6 (IPv6), Novell Internetwork Packet Exchange (IPX), AppleTalk, and Connectionless Network Service (CLNS/DECNet)
3. IPv4 is going to be replaced by IPv6. What is the most significant difference between the two?
Although answers will vary, the most significant difference between IPv4 and IPv6 is length. The address space for IPv4 is 32 bit, whereas IPv6 is 128 bit.
4. List three basic characteristics of IPv4.
IPv4 is connectionless, best effort (unreliable), and media independent.
5. If out-of-order or missing packets create problems for the application using the data, which services have to resolve these issues?
The upper-layer services resolve these issues.
6. In some cases, an intermediary device, usually a router, will need to split up a packet when for- warding it from one media to a media with a smaller maximum transmission unit (MTU). What is this process called?
Fragmentation
Vocabulary Exercise: Completion
Fill in the blanks for the following questions.
1. Each route that a packet takes to reach the next device is called a hop.
2. Intermediary devices that connect the networks are called routers.
3. Any individual IP packet can be communicated electrically over cable, as optical signals over
fiber, or wirelessly as radio signals.
4. The header of an IPv4 packet does not include fields required for reliabledata delivery. There are no acknowledgments of packet delivery. There is no error controlfor data.
Vocabulary Exercise: Define
Table 5-1 lists the six key fields in a typical IPv4 header. Fill in the purpose of each field.
Table 5-1 Key Fields of IPv4 Header
Field Purpose
IP source address IPv4 address of host sending the packet: enables the destination host to respond to the source if required.
IP destination address IPv4 address of host to receive the packet: enables routers at each hop to for- ward the packet towards the destination.
Time-to-Live (TTL) Number of hops before packet is dropped: This value is decremented at each hop to prevent packets being passed around the network in routing loops.
Type-of-Service (ToS) Data quality of service (QoS) priority: Enables router to give priority to voice and network route information over regular data.
Protocol The data payload protocol type: Denotes whether the data is a UDP datagram or TCP segment, because these transport layer protocols manage the receipt of their protocol data units (PDU) differently.
Fragment offset These 13 bits allow a receiver to determine the place of a particular fragment in the original IP datagram.