9 SUPPORTING TCP/IP, DNS USING WINDOWS XP 9.1 Introduction to TCP/IP 9.2 Configuring and Troubleshooting TCP/IP 9.2.1 Understanding IP address 9.2.2 IP Addresses : Networks and Hosts 9.2.3 Subnet Mask 9.2.4 Special Address 9.2.5 Private Address 9.3 Assigning IP Address 9.4 Automatic Private IP Addressing 9.5 Testing TCP/IP Connections 9.6 Domain Name System 9.6.1 Domain Namespace 9.7 Summary 9.8 Exercises Objectives At the end of this chapter students should be able to: § Explain the concept of the TCP/IP addresses § Determine the IP classes, special address and subnet address § Explain the usage of Automatic Private IP Addressing. § Identify the network troubleshooting tools § Identify the concept of Domain Name System
Transcript
9 SUPPORTING TCP/IP, DNS USING WINDOWS XP 9.1 Introduction to TCP/IP 9.2 Configuring and Troubleshooting TCP/IP
9.2.1 Understanding IP address 9.2.2 IP Addresses : Networks and
Hosts 9.2.3 Subnet Mask 9.2.4 Special Address 9.2.5 Private Address
9.3 Assigning IP Address 9.4 Automatic Private IP Addressing 9.5 Testing TCP/IP Connections 9.6 Domain Name System
9.6.1 Domain Namespace
9.7 Summary 9.8 Exercises
Objectives At the end of this chapter students should be able to:
§ Explain the concept of the TCP/IP addresses § Determine the IP classes, special address and
subnet address § Explain the usage of Automatic Private IP
Addressing. § Identify the network troubleshooting tools § Identify the concept of Domain Name System
CLIENT OPERATING SYSTEM
2
9.1 INTRODUCTION TO TCP/IP
TCP/IP (Transmission Control Protocol/Internet Protocol) is the communication language or protocol for communication between computers connected to the Internet. It is a standard defines how electronic devices (like computers) should be connected to the Internet, and how data should be transmitted between them.
Additionally, TCP/IP uses the client/server communication in which a computer user (a client) requests and the server provides a service (such as sending a Web page) in the network. This communication is primarily point-to-point, meaning each communication is from one point (or host computer) in the network to another point or host computer.
The origins of TCP/IP
TCP/IP originated out of the investigative research into networking protocols that the Department of Defense (DoD) initiated in 1969. It indicated the need for a wide-area communication system, covering the United States and allowing the interconnection of heterogeneous hardware and software systems
In 1967 the Stanford Research Institute was contracted to develop the suite of protocols for this network, initially to be known as ARPANet. Other participants in the project included the University of Berkeley (California) and the private company BBN. Development work commenced in 1970 and by 1972 approximately 40 sites were connected via TCP/IP.
In 1973 the first international connection was made and in 1974 TCP/IP was released to the public. Initially the network was used to interconnect governments, military and educational sites together. Slowly, as time progressed, commercial companies were allowed access and by 1990 the backbone of the Internet, as it was now known, was being extended into one country after the other.
Without TCP/IP, no Internet access is possible for us.
Figure 9-1 TCP/IP communication
Client
Client
Server
Support ing TCP/ IP, DNS Using Windows XP
3
9.2 CONFIGURING AND TROUBLESHOOTING TCP/IP
In order to configure the TCP/IP communication, you need to familiarize with IP address, subnets and gateways.
If definitions are helpful to you, use these vocabulary terms to get you started:
§ IP -- The network protocol used for sending network packets over a TCP/IP network or the Internet.
§ Address -- The unique number ID assigned to one host or interface in a
network. § Subnet -- A portion of a network sharing a particular subnet address. § Subnet mask -- A 32-bit number used to distinguish which portion of
an address refers to the network and which part refers to the host. § Gateways -- If a computer needs to communicate with a host on
another network, it will usually communicate through a device called a router. In TCP/IP terms, a router that is specified on a host, which links the host's subnet to other networks, is called a default gateway.
On a TCP/IP network, each device such as computer, router, or other device with a network connection is referred as a host.
9.2.1 Understanding IP Address
Every machine on the Internet has unique identifying number, called an IP Address. It is much the same way as a street address identifies a house on a street. A typical IP Address looks like this:
• Example : 192.68.20.50 To make it easier for us humans to remember, IP addresses are normally expressed in decimal format as a dotted decimal number like the one above. But computers communicate in binary form. Look at the same IP Address in binary: 11000000. 01000100. 00010100. 00110010 (See Section 9.2.1.1 to know how the converting the binary into decimal form) The four numbers in an IP Address are called octets because they each have eight positions when viewed in binary form. If you add all the positions together, you get 32, which is why IP Addresses are considered as 32-bit numbers.
Remember! An IP address is a 32-bit number that uniquely identifies a host (computer or other device, such as a printer or router) on a TCP/IP network.
Octet is an 8-bit number, 4 of which comprise a 32-bit IP address. Each of the eight positions can have two different states (1 or 0) the total number of possible combinations per octet is 28 or 256. So each octet can contain any value between 0 and 255. Combine the four octets and you get 232 or a possible 4,294,967,296 unique values!
9.2.1.1 Converting octets to decimal
Here is how binary octets convert to decimal: The right most bit, or least significant bit, of an octet will hold a value of 20. The bit just to the left of that will hold a value of 21. This continues until the left-most bit, or most significant bit, which will hold a value of 27.
The 32 binary bits are broken into four octets. Each octet is converted to decimal and separated by a period (dot). For this reason, an IP address is said to be expressed in dotted decimal format (example, 172.16.81.100).
Example 1 So if all binary bits are a one, the decimal equivalent would be 255 as shown here:
1 1 1 1 1 1 1 1 27 26 25 24 23 22 21 20
128 64 32 16 8 4 2 1 (128+64+32+16+8+4+2+1=255)
Support ing TCP/ IP, DNS Using Windows XP
5
Example 2
Here is a sample octet conversion when not all of the bits are set to 1.
9.2.2 IP Addresses: Networks and hosts The octets are used to create classes of IP address that can be assigned to particular business, government or other entity based on size and need. The octets can be split into two sections: Network ID (Net ID) and Host ID.
• Network ID – it is always contains the first octet. It is used to identify the network that a computer belongs to.
• Host ID – it is always contains the last octet. It identifies the actual computer on the
network. These octets are broken down to provide an addressing scheme that can accommodate large and small networks. There are five different classes of networks, A to E and certain special addresses.
IP Classes <---8 bits ----> <---8 bits ----> <---8 bits ----> <---8 bits ----> Class A N H H H Class B N N H H Class C N N N H Class D Multicast Class E Experimental
Table 9-1 The position of Network ID and Host ID
N = Network ID H = Host ID
CLIENT OPERATING SYSTEM
6
Figure 9-2 Range of IP Classes This document focuses on addressing classes A to C, since classes D and E are reserved and discussion of them is beyond the scope of this section. For example the positions of octets for IP address on each class can be represented like this: (Refer Figure 9-2).
IP classes Explanations Class A
This class is for very large networks, such as a major international company might have. IP addresses with a first octet from 1 to 126 are part of this class (27=126). The other three octets are used to identify each host.
This means that there are 126 Class A networks each with 16,777,214 (224 -2) possible hosts for a total of 2,147,483,648 (231) unique IP addresses. In Class A networks, the high order bit value (the very first binary number) in the first octet is always 0. Example : 115.24.53.107
Net Host 115 24.53.107
* Why we should deduct 2 from the host ID? (Refer 224 -2). In this case, the range of the class A is 1.0.0.0 - 127.255.255.255. Two addresses that cannot be used because binary addresses with a host portion of all ones and all zeros are invalid. The zero address is invalid because it is used to specify a network without specifying a host. Example 1.0.0.0 The 255 address (in binary notation, a host address of all ones) is used to broadcast a message to every host on a network. Example: 127.255.255.255
* 27 * 224
Support ing TCP/ IP, DNS Using Windows XP
7
IP classes Explanations Class B
Class B is used for medium-sized networks. A good example is a large college campus. IP addresses with a first octet from 128 to 191 are part of this class. Class B addresses also include the second octet as part of the Net identifier. The other two octets are used to identify each host.
This means that there are 16,384 (214) Class B networks each with 65,534 (216 -2) possible hosts for a total of 1,073,741,824 (230) unique IP addresses. Class B networks have a first bit value of 1 and a second bit value of 0 in the first octet. Example : 145.24.53.107
Net Host 145.24. 53.107
IP classes Explanations Class C
Class C addresses are used for small to mid-size businesses. IP addresses with a first octet from 192 to 223 are part of this class. Class C addresses also include the second and third octets as part of the Net identifier. The last octet is used to identify each host.
This means that there are 2,097,152 (221) Class C networks each with 254 (28 -2) possible hosts for a total of 536,870,912 (229) unique IP addresses. Class C networks make up an eighth of the total available IP addresses. Class C networks have a first bit value of 1, second bit value of 1 and a third bit value of 0 in the first octet. Example : 195.24.53.107
Net Host 195.24.53. 107
* 214 * 216
* 221 * 28
CLIENT OPERATING SYSTEM
8
IP classes Explanations Class D
It is used for multicasts. It has a first bit value of 1, second bit value of 1, third bit value of 1 and fourth bit value of 0. The other 28 bits are used to identify the group of computers the multicast message is intended for. Example : 224.24.53.107
Net Host 224. 24.53.107
IP classes Explanations Class E
Class E is used for experimental purposes only. It has a first bit value of 1, second bit value of 1, third bit value of 1 and fourth bit value of 1. The other 27 bits are used to reserve for future use. Example : 240.24.53.107
Net Host 240. 24.53.107
9.2.3 Subnet Mask
Subnet mask is required for TCP/IP to work. The subnet mask is used by the TCP/IP protocol to determine whether a host is on the local subnet or on a remote network. In TCP/IP, the parts of the IP address that are used as the network and host addresses are not fixed, so the network and host addresses above cannot be determined unless you have more information. This information is supplied in another 32-bit number called a subnet mask. Table 9-2 shows the subnet mask for each IP class.
Class Range of First Octet
Number of Available Network
Number of Host per Network
Subnet Mask
A 0-127 126 16,777,214 255.0.0.0 B 128-191 16,384 65,534 255.255.0.0 C 192–223 2,097,152 254 255.255.255.0 D 224–239 N/A N/A N/A E 240–255 N/A N/A N/A
Table 9-2 Subnet mask
Significantly, the subnet mask help to determine which portion of an IP address is the network and host parts of the address. The network bits are represented by the 1s in the mask, and the host bits are represented by the 0s. Figure 9-3 depicts a single IP address shown in both decimal and binary format.
Support ing TCP/ IP, DNS Using Windows XP
9
Figure 9-3 The subnet mask separates the host ID and the network ID Example: Given an IP address is 192.168.123.132 (class C IP address). What is the subnet mask for this IP address? * First, you need to determine the network address and the host address of the IP address. For this example, the network address for the IP address is 192.168.123.0 and the host address is 0.0.0.132. (Refer section 9.2.2 -- IP Addresses: Networks and hosts) The subnet mask is 255.255.255.0 (Refer Table 9-2, this is the subnet mask for class C). It is not obvious what this number means unless you know that 255 in binary notation equals 11111111; so, the subnet mask is:
11111111.11111111.11111111.0000000 Lining up the IP address and the subnet mask together, the network and host portions of the address can be separated:
11000000.10101000.01111011.10000100 -- IP address (192.168.123.132) 11111111.11111111.11111111.00000000 -- Subnet mask (255.255.255.0)
The first 24 bits (the number of ones in the subnet mask) are identified as the network address, with the last 8 bits (the number of remaining zeros in the subnet mask) identified as the host address. This gives you the following:
So now you know, for this example using a 255.255.255.0 subnet mask, which the network ID is 192.168.123.0, and the host address is 0.0.0.132. When a packet arrives on the 192.168.123.0 subnet (from the local subnet or a remote network), and it has a destination address of 192.168.123.132, your computer will receive it from the network and process it. Almost all decimal subnet masks convert to binary numbers that are all ones on the left and all zeros on the right. Some other common subnet masks are: Decimal Binary 255.255.255.192 1111111.11111111.1111111.11000000 255.255.255.224 1111111.11111111.1111111.11100000
CLIENT OPERATING SYSTEM
10
9.2.4 Special Address Below are the special addresses in the network.
Special Address Explanations Default network
The IP address of 0.0.0.0 is used for the default network.
Loopback address
The IP address 127.0.0.1 is used as the loopback address. This means that it is used by the host computer to send a message back to itself. It is commonly used for troubleshooting and network testing.
Broadcast address
Messages that are intended for all computers on a network are sent as broadcasts. These messages always use the IP address 255.255.255.255.
Table 9-3 Special Address
9.2.5 Private Address Every network interface that is connected directly to the Internet must have an IP address registered with the Internet Assigned Numbers Authority (IANA). Private addressing prevents IP address conflicts between addresses. IANA has set aside three address ranges for use by private or non-Internet connected networks. § 10.0.0.0 to 10.255.255.255 § 172.16.0.0 to 172.31.255.255 § 192.168.0.0 to 192.168.255.255
Private Address You can choose whichever range you like to use for your network. None of these addresses is officially assigned to publicly accessible Internet host. If you are configuring a private network that is connected to the Internet or one that exists behind a firewall or proxy server, you can configure devices on your network with private addresses and have only the public address configured on the interface that is visible to the Internet
Support ing TCP/ IP, DNS Using Windows XP
11
9.3 ASSIGNING IP ADDRESS
Windows XP Professional provides four methods for assigning IP addresses to TCP/IP clients: 1) Static IP Addressing
Allows you to manually configure the IP address if DHCP and APIPA are not available or are not feasible. This method can be time-consuming and prone to error, especially on larger networks.
2) Dynamic Host Configuration Protocol (DHCP)
Provides automatic configuration of IP addresses and other configuration options (autoconfiguration) for clients in a network with one or more DHCP servers. This is the default addressing method in Windows XP Professional. These addresses might change over time. 3) Automatic Private IP Addressing (APIPA)
Automatically assigns a private IP address to clients where no DHCP server is available. When communicating within their own subnet, computers using APIPA addresses can communicate only with other computers using APIPA addresses. For more information about APIPA, see “APIPA “ later in this chapter.
4) Alternate IP Configuration
Allows a single interface to make use of more than one IP address as long as only one is used at a time. New in Windows XP Professional, Alternate IP Configuration allows the user to configure a Windows XP Professional–based computer to use one address (either a specified static address or an automatically configured one) and then if that attempt is not successful, to make another preconfigured attempt.
9.3.1.1 LAB: Configure TCP/IP for static addressing The IP addresses that are assigned manually are called static IP addresses. These addresses are fixed and it will not change unless you change them. When you assign a static IP address, you need to tell the computer the IP address you want to use, the subnet mask for this IP address and if necessary, the default gateway to use for this internetwork communication.
CLIENT OPERATING SYSTEM
12
Static IP addressing involves manually setting an IP address and associated information in the TCP/IP Properties page of Control Panel’s Network applet on each computer. This is generally useful only for very small networks, where few devices move around or are added or removed.
One of the biggest drawbacks to this method is that an administrator needs to keep a definitive list of which address is assigned to which host on the network, including network-attached printers and print servers, routers and switches, servers, and computers
For example, a computer on the network segment 10.0.10.0 with the a subnet mask of 255.255.255.0, the first three bits represent the network ID, the address range you have available for computer hosts is from 10.0.10.1 to 10.0.10.254. In this range, the address 10.0.10.255 is reserved for network broadcast. To configure TCP/IP for static IP address, complete the following steps:
1. Click Start, and then click Control Panel. 2. In the Control Panel window, click Network and Internet Connections.
Figure 9-4 Network and Internet Connection in the Control Panel Windows
3. In the Network and Internet Connections window, click Network Connections.
Support ing TCP/ IP, DNS Using Windows XP
13
Figure 9-5 Click Network Connection in the Network and Connections Selection
4. Right click Local Area Connection, and then click Properties.
Figure 9-6 Click the LAN or High-Speed Internet in the Network Connection
5. In the Local Area Connection Properties dialog box, click Internet Protocol (TCP/IP), verify that the check box to its left is selected, and then click Properties.
CLIENT OPERATING SYSTEM
14
Figure 9-7 Check the TCP/IP to enable IP network address
6. In the Internet Protocol (TCP/IP) Properties dialog box, in the General tab, click Use the following IP address option. Enter an IP address that is on the same subnet as the LAN IP address on your router.
Example:
A computer on the network segment 192.168.2.0 with a subnet mask of 255.255.255.0, the address range you have available for computer hosts is from 192.168.2.1 to 192.168.2.254. In this range, the address 192.168.2.255 is reserved for network broadcast. At the IP address and default gateway, you can put the IP address that is not in use on the network. (eg. the IP address is 192.168.2.122, while the default gateway is 192.168.2.2 ). Regarding on the DNS server addresses, the IP address of 202.188.0.132 and 202.188.0.133 are given by ISP provider. Additionally, you may also contact the network administrator in your company about the DNS server address.
Click OK twice.
Support ing TCP/ IP, DNS Using Windows XP
15
Figure 9-8 Insert the appropriate IP address settings The DNS Server address can also be set similarly to the default gateway. If the DNS Server address you wrote down is the same as your default gateway address, it may mean the router is “caching” the DNS server addresses for you, or the router will relay the requests for DNS information to your ISP’s DNS servers “dynamically.” * What if there are no DNS Server addresses listed in the above procedures? * What if using the router’s Default Gateway address doesn’t work? In this case, you need to call your ISP and ask them for two of their DNS Server addresses. One for a “Preferred DNS Server” and one for the “Alternate DNS Server”.
A gateway is simply a device on a network that acts as an entrance to another network. In more technical terms, a gateway is a routing device that knows how to pass traffic between different subnets and networks. The default gateway is typically very similar to your IP address, in that many of the numbers may be the same. However, the default gateway is not your IP address. A default gateway is simply a gateway that meets certain criteria:
• It is on the same subnet as your computer. • It is the gateway that your computer relies on when it doesn't already
know which route to send traffic through.
CLIENT OPERATING SYSTEM
16
7. Click OK to close the Local Area Connection Properties dialog box, and then close the Network Connections window.
9.3.1.2 LAB: Configure TCP/IP for dynamic addressing To configure TCP/IP for automatic/dynamic addressing, complete the following steps:
1. Use the same step 1 until step 5 above.
2. In the Internet Protocol (TCP/IP) Properties dialog box, in the General tab, click Obtain an IP address automatically option.
Figure 9-9 IP setting is done automatically for the dynamic addressing
3. Click OK to close the Local Area Connection Properties dialog box, and then close the Network Connections window.
Uses of dynamic addressing
Dynamic IP Addresses assigned, on LANs or most broadband networks, by Dynamic Host Configuration Protocol (DHCP) servers are used because it reduces the administrative burden of assigning static addresses within a network. In most desktop operating systems, dynamic IP configuration is enabled by default. Dialup and some broadband networks do not use DHCP
Support ing TCP/ IP, DNS Using Windows XP
17
9.4 AUTOMATIC PRIVATE IP ADDRESSING (APIPA) Automatic Private IP Addressing (APIPA) enables a computer to automatically assign itself an IP address when there is no Dynamic Host Configuration Protocol (DHCP) server available to perform that function. APIPA serves as a DHCP server failover mechanism and makes it easier to configure and support small local area networks. If no DHCP server is currently available, the computer selects an IP address from a range of addresses (from 169.254.0.0 - 169.254.255.255) reserved by the Internet Assigned Numbers Authority (IANA) for that purpose. Once the computer has assigned itself an IP address, it can communicate over TCP/IP with other computers on the LAN. DHCP messages notify the user when they are switched between DHCP addressing and APIPA.
Figure 9-10 APIPA assigns IP addresses automatically. The process for the APIPA feature, shown in Figure 9-10, is explained in the following steps:
1. Windows XP Professional TCP/IP attempts to find a DHCP server on the attached network to obtain a dynamically assigned IP address.
2. In the absence of a DHCP server during startup (for example, if the server is down for
maintenance or repairs), the client cannot obtain an IP address.
3. APIPA generates an IP address in the form of 169.254.x.y (where x.y is the client’s randomly generated unique identifier) and a subnet mask of 255.255.0.0.
CLIENT OPERATING SYSTEM
18
Examples of Where APIPA May Be Useful
• No Previous IP Address and no DHCP Server When your Windows-based computer (configured for DHCP) is initializing, it broadcasts three or more "discover" messages. If a DHCP server does not respond after several discover messages are broadcast, the Windows computer assigns itself a Class B (APIPA) address. Then the Windows computer will display an error message to the user of the computer (providing it has never been assigned an IP address from a DHCP server in the past). The Windows computer will then send out a Discover message every three minutes in an attempt to establish communications with a DHCP server.
• Previous IP Address and no DHCP Server
The computer checks for the DHCP server and if none are found, an attempt is made to contact the default gateway. If the default gateway replies, then the Windows computer retains the previously-leased IP address. However, if the computer does not receive a response from the default gateway or if none are assigned, then it uses the automatic private IP addressing feature to assign itself an IP address. An error message is presented to the user and discovers messages are transmitted every 3 minutes. Once a DHCP server comes on line, a message is generated stating communications have been re-established with a DHCP Server.
• Lease Expires and no DHCP Server
The Windows-based computer tries to re-establish the lease of the IP address. If the Windows computer does not find a DCHP server, it assigns itself an IP address after generating an error message. The computer then broadcasts four discover messages, and after every 5 minutes it repeats the whole procedure until a DHCP server comes on line. A message is then generated stating that communications have been re-established with the DHCP Server.
Support ing TCP/ IP, DNS Using Windows XP
19
9.4.1.1 LAB: Disable APIPA By default, the APIPA feature is enabled. However, you can disable it by specifying an alternate configuration to use if a DHCP server cannot be located. The alternate configuration is useful when a computer is used on multiple networks, one of which does not have a DHCP server and does not use an automatic private IP addressing configuration. To specify alternate configuration, follow these steps:
1. Click Start, click Control Panel. In the Control Panel window, click Network and Internet Connections.
2. In the Network and Internet Connections window, click Network Connection. 3. Right click Local Area Connection and select Properties. 4. In the Local Area Connection Properties dialog box, click Internet Protocol
(TCP/IP), verify that the check box to its left is selected, and then click Properties. 5. Click Alternate Configuration tab. Specify the alternate TCP/IP configuration.
Figure 9-11 Put the assigned IP setting for the alternate configuration
9.5 TESTING TCP/IP CONNECTIONS
Windows XP provides a number of TCP/IP tools for troubleshooting network connectivity problems. Below are the tools to troubleshoot the connection:
• Ping This tool allows you to check for connectivity between devices on a network. • Ipconfig This tool uses to view current TCP/IP configuration information for a computer.
CLIENT OPERATING SYSTEM
20
• Tracert This tool help you figure out exactly where along the route the breakdown happened. • Pathping This tool is a combination of ping and tracert. This tool can display information about packet lost between the source and the destination. It is also used to determine which particular router or subnet might be having network problem.
Your Computer Configuration
When you want to troubleshoot a TCP/IP networking problem, first check the TCP/IP configuration of the computer that is experiencing the problem.
9.5.1.1 LAB: To Test Connections by Using Ping.exe You can use the ping command as a troubleshooting tool to sequentially test connectivity to various network resources. To ping a network host directly:
1. Click Start, click Run, type cmd, and then press ENTER. 2. Type ping IP address of the remote network host (for example, ping 192.168.2.117)
or ping host name (eg. ping www.cosmopoint.com.my), and then press ENTER.
Figure 9-12 Use ping to test the network connectivity
Check for a reply that may look like this: 1. If this message displays “ Reply from 192.168.1.104: bytes=32 time=40ms TTL=61 It means that the server is available on the network. 2. If you are unable to contact the resource, you can troubleshoot the
connection by using the ping command to test connectivity to various network resources:
• Ping the loopback address (by using the ping 127.0.0.1 command) to
verify that TCP/IP is installed and working correctly on the local computer.
• Ping the IP address of the local computer to verify that it was added to the network correctly.
• Ping the IP address of the default gateway to verify that the gateway is functional and it is possible to connect to a local host on the local network. You can obtain the IP address of the local default gateway by using the ipconfig command.
• Ping the IP address of another remote host to verify that you can communicate through a router.
9.5.1.2 LAB: To View the TCP/IP Configuration by Using the Ipconfig.exe Tool
1. Click Start, click Run, type cmd, and then press ENTER. 2. At the command prompt, type ipconfig, and then press ENTER. This command
displays your computer's DNS suffix, IP address, subnet mask, and default gateway.
Figure 9-14 The ipconfig command ensure your network adapter is not in a Media disconnected state.
3. If you need more information and want to display a detailed configuration report, type ipconfig /all at the command prompt, and then press ENTER.
CLIENT OPERATING SYSTEM
22
Figure 9-15 ipconfig /all displays a detailed configuration report
Confirm that your computer has the appropriate settings for DNS and WINS servers, an available IP address, the proper subnet mask, the proper default gateway, and the correct host name.
9.6 DOMAIN NAME SYSTEM
Domain Name System (DNS) is a naming system that is used in TCP/IP networks to translate computer names to IP addresses. This will be easier as user no need to remember 12 digit numbers. When you visit a web site such as www.cosmopoint.com.my, the name is translated to a number by a DNS process (Domain Name Server).
DNS servers are responsible for translating domain names into TCP/IP addresses and update each other with new domain names. When a new domain name is registered together with a TCP/IP address, DNS servers all over the world are updated with this information.
Without DNS, you would not be able to type in names, but would have to remember the numerical IP Addresses in order to get anywhere on the Internet. DNS makes it easy to locate computers and other resources on IP-based network.
Another key element of the Domain Name System are:
• DNS Servers run by Companies • Internet Service Providers.
Every time you connect to a site, you are asking your ISP's DNS Server to resolve, or convert, the hostname such as www.google.com to an IP address such as 216.239.51.99. If
your ISP's name server is not working or can not be reached, then you will not be able to traverse the Internet using hostnames, but instead would have to use their IP Address equivalent.
9.6.1 Domain Namespace
The domain namespace is the naming scheme that provides the hierarchical structure for the DNS database. It is based on the concept of a tree of named domains. Each level of the tree can represent either a branch or a leaf of the tree. A branch is a level where more than one name is used to identify a collection of named resources. A leaf represents a single name used once at that level to indicate a specific resource. The DNS database is indexed by name, so each domain must have a name. As you add domains to the hierarchy, the name of the parent domain is added to its child domain (called a subdomain). Consequently, a domain’s name identifies its position in the hierarchy.
Figure 9-16 The domain namespace is hierarchical in structure The hierarchical structure of the domain namespace consists of:
9.6.1.1 Root Domain At the top of the DNS hierarchy, there is a single domain called the root domain, which is represented by a single period.
9.6.1.2 Top-Level Domains Top-level domains are two, three, or four character name codes. Top-level domains are grouped by organization type or geographic location. Top-level domains are controlled by the Internet Architecture Board (IAB), an Internet authority controlling the assignment of domain names, among other things. Table 9-4 provides some examples of top-level domain names.
Top-Level Domain Description gov Government organizations com Commercial organizations edu Educational institutions org Noncommercial organizations au Country code of Australia net Networking organization mil Military operations
Table 9-4 Top-level domains
9.6.1.3 Second-Level Domains Anyone can register a second-level domain name. These domains are registered to individuals and organizations by a number of different domain registry companies. After registering a second-level domain name, you can create as many subdomains of that domain name as you want.
If you registered the domain name cosmopoint.com, you could create subdomains such as cas.cosmopoint.com.
9.6.1.4 Host Names Host names refer to specific computers on the Internet or a private network. A host name is the leftmost portion of a fully qualified domain name (FQDN), which describes the exact position of a host within the domain hierarchy.
Support ing TCP/ IP, DNS Using Windows XP
25
The host name does not have to be the same as the computer name. By default, TCP/IP setup uses the computer name for the host name, replacing illegal characters, such as the underscore (_), with a hyphen (-).
The domain name such as cas.cosmopoint.com identifies the cas domain as a subdomain of the cosmopoint.com domain and cosmopoint as a subdomain of the com domain. Computer1.cas.cosmopoint.com is a FQDN. DNS uses a host’s FQDN to resolve a name to an IP address.
9.6.2 Domain-Naming Guidelines
To create a domain namespace, consider the following domain guidelines and standard naming conventions:
1. Limit the number of domain levels. Typically, DNS host entries should be three or four levels down the DNS hierarchy and no more than five levels down the hierarchy. The numbers of levels increase the administrative tasks.
2. Use unique names. Each subdomain must have a unique name within its parent
domain to ensure that the name is unique throughout the DNS namespace.
3. Use simple names. Simple and precise domain names are easier for users to remember. They also enable users to search intuitively and locate Web sites or other computers on the Internet or an intranet.
4. Avoid lengthy domain names. Domain names can be up to 63 characters, including
periods. The total length of an FQDN cannot exceed 255 characters. Casesensitive naming is not supported.
5. Use standard DNS characters and Unicode characters. Windows 2000 Server and
Windows Server 2003 support the following standard DNS characters: a–z, 0–9, and the hyphen (-), as defined in RFC 1035.
6. The DNS Service also supports the Unicode character set. The Unicode character set
includes additional characters not found in the American Standard Code for Information Interchange (ASCII) character set; these additional characters are required for languages such as French, German, and Spanish.
CLIENT OPERATING SYSTEM
26
9.6.2.1 LAB: Configuring a DNS Client The DNS Client acts like a local DNS server, and is used whenever an application requires to resolve a Domain Name System(DNS) name. If an application wants to connect to www.google.com, then it requests the DNS client for it to convert it to an IP address. If the DNS client doesn't recognize the domain it passes the request to the network DNS Server (Port 53), but caches the reply for later use by the same or other applications and thus increases the speed of future DNS lookups and causes less load on the network DNS Server. To configure your computer as a DNS client, use the following steps:
1. Click Start, click Control Panel. Click Network and Internet Connections. 2. In the Network and Internet Connections window, click Network Connections. 3. Right-click Local Area Connection and then click Properties. Windows XP
Professional displays the Local Area Connection Properties dialog box. 4. Click Internet Protocol (TCP/IP), and then click Properties. Select one of the two
following options:
§ Obtain DNS Server Address Automatically. If you select this option, you must have a DHCP server available on your network to provide the IP address of a DNS server.
§ Use The Following DNS Server Addresses. If you select this option, you must
type in the IP addresses of the DNS servers you want this client to use. You can enter a Preferred DNS Server address and an Alternate DNS Server address.
5. To set additional configuration, click Advanced.
Figure 9-17 Click the Advanced button to set an additional configuration
6. Advanced TCP/IP Settings dialog box appear, click the DNS tab. Table 9-5 explains
all of provided options.
Figure 9-18 DNS server must be configured for resolving DNS names
For DNS clients to operate effectively, a prioritized list of DNS name servers must be configured for each computer to use when processing queries and resolving DNS names. In most cases, the client computer contacts and uses its preferred DNS server, which is the first DNS server on its locally configured list.
Option Explanation
Add To enter additional DNS server addresses to the list of servers that service this computer to resolve DNS domain names.
Edit To modify the addresses listed.
Remove To delete the address of a DNS server from the list.
Up-pointing arrow or down-pointing arrow
To change the order of the servers listed.
Append Primary And Connection Specific DNS Suffixes
Tells the DNS resolver to append the client name to the primary domain name, as well as the domain name defined in the DNS Domain Name field.
Append Parent Suffixes Of The Primary DNS Suffix
This configuration causes the DNS resolver to drop the leftmost portion of the primary DNS suffix and attempt to use the resulting domain name.
CLIENT OPERATING SYSTEM
28
Append These DNS Suffixes (In Order)
To specify a list of domains for the DNS resolver to try.
Register This Connection's Addresses In DNS
Cause the client itself to attempt to dynamically register the IP addresses via DNS with its full computer name.
Use This Connection's DNS Suffix In DNS Registration
Uses DNS dynamic updates to register the IP addresses and the connection-specific domain name.
Table 9-5 Advanced Setting in the TCP/IP
Support ing TCP/ IP, DNS Using Windows XP
29
9.7 SUMMARY
1. Each TCP/IP host is identified by a logical IP address that identifies a computer’s
location on the network. The IP address is composed of a network ID and a host ID.
2. A subnet mask determines which portion of the IP address is the network ID and which portion is the host ID.
3. A static IP address is a manually entered address. You should assign a static IP
address to selected network computers, such as the computer running the DHCP Service.
4. Windows XP Professional can obtain an IP address automatically from a DHCP
server on the network. Using automatic addressing reduces the likelihood of errors being introduced when configuring static addresses.
5. Windows XP Professional can assign itself an IP address using APIPA if a DHCP
server is not available. Computers enabled with APIPA can communicate only with computers on the same subnet that also have addresses of the form 169.254.x.y.
6. Specifying an alternate TCP/IP configuration is useful when a computer is used on
multiple networks, one of which does not have a DHCP server and does not use an automatic private IP addressing configuration.
7. The DNS database is indexed by name, so each domain/node must have a name. The
hierarchical structure of the domain namespace consists of a root domain, top-level domains, second-level domains and host names.
8. When creating a domain namespace, you should use certain guidelines, such as
limiting the number of domain levels and using unique and simple names.
9. When configuring a DNS client in an environment in which there are DNS name servers, you can configure the client to obtain the address of the DNS server automatically from a DHCP server or you can manually enter multiple addresses for DNS servers.
CLIENT OPERATING SYSTEM
30
9.8 EXERCISES
True or False 1. All devices in the domain must have same IP address 2. Portions of IP address are network ID and host ID 3. Static IP address is dynamically assigned by DHCP server. 4. Hosts depend on second number called subnet mask to
determine which portion of an IP address is network ID and host ID.
5. The range of class A is 192.168.0.0 to 192.168.255.255. 6. APIPA assigns an IP address and subnet mask only. 7. 169.254.0.0 through 169.254.255.255 is reserved for
APIPA to avoid conflict with routable addresses. 8. Pathping is a tool that to troubleshoot the network
connection. 9. gov is a second-level domain names. 10. The domain namespace consists of a root domain, top level
domains, second-level domains and host names.
True □
True □
True □
True □
True □
True □
True □
True □
True □
True □
False □
False □
False □
False □
False □
False □
False □
False □
False □
False □
Support ing TCP/ IP, DNS Using Windows XP
31
Fill in the Blanks 1. The _______________________ is a portion of the IP address starting from the left that
identifies the network segment on which a host is located. 2. The _________________________ is the portion of the IP address that identifies a
particular host on a network segment. The host ID for each host must be unique within the network ID.
3. _______________________ enable a computer to automatically assign itself an IP
address when there is no Dynamic Host Configuration Protocol (DHCP) server. 4. ______________ refers to specific computers on the Internet or private network. 5. The domain namespace consist of ____________________________________________. Multiple Choice Questions 1. Which of the following are second-level domain names?
A. gov B. Microsoft.com C. Au D. ed.gov
2. Which of the following statements describe IP addresses?
A. IP addresses are 64-bit addresses that identify a TCP/IP host. B. Each network adapter card in a computer running TCP/IP requires a unique IP
address. C. 192.168.2.121 is example of a class C IP address. D. The host ID in an IP address is always the last two octets in the address.
3. Which tools are not purposely used for network troubleshooting?
A. Ping B. ScanDisk C. Defragmenter D. Pathping
4. Which of the following statements correctly describes DNS root domains?
A. The root domain is at the top of the hierarchy. B. The root domain is at the bottom of the hierarchy. C. The root domain is represented by a two- or three-character name code. D. The root domain is represented by a period (.)
CLIENT OPERATING SYSTEM
32
Subjective Questions 1. What is TCP/IP? 2. Why would you assign a computer a static IP address?
3. What is the purpose of a subnet mask? 4. What is DNS and what is it used for?
5. Explain the hierarchical structure of the domain namespace. 6. You are an administrator for a company named Winpc. Kamarul, a user in the R&D
department, calls you on Friday afternoon to report that he cannot connect to any resources on the local network. After verifying the other users in his department can connect to the network, you visit Kamarul’s computer, open the Command Prompt window, and type ipconfig /all. You get the following results:
Ethernet adapter Local Area Connection: Description ……………….. CNet PRO200WL PCI Fast Ethernet Adapter Physical Address………….. 00-80-AD-78-82-0B DHCP Enabled……………. Yes IP Address………………… 169.254.103.52 Subnet Mask………………. 255.255.0.0 Default Gateway…………... DNS Server………………..
i. What do these results tell you? ii. What would be your first troubleshooting step? What should you do if that first
step does not work? Practical Questions
1. Complete the following table which provides practice in converting a number from
binary notation to decimal format. (Follow example below)
3. Express in binary format and determine the class IP address.
i. Example 145.32.59.24 = 10010001.00100000.00111011.00011000 – class B ii. 200.42.129.16 iii. 14.82.19.54
Practise: Configure TCP/IP to Use a Static IP Address In this practise, you will use TCP/IP tools to verify your computer’s configuration. Then, you configure to use a static IP address and verify your new configuration. If your computer is part of existing network, use the following table to record IP address, subnet mask and default gateway. If you are not a network, you can use the suggested value.
Variable value Suggested value Your value Statistic IP address 192.168.1.201 Subnet mask 255.255.0.0 Default gateway (if required)
None
Exercise: Verify a computer’s TCP/IP Configuration 1. Click Start. Click Run and type ipconfig /all. Then press Enter. 2. Use the information displayed, complete the following table as possible:
Local Area Connection Setting Your value Host name Primary DNS Suffix Connection-specific DNS suffix description Physical Address DHCP Enabled Autoconfiguration enabled Autoconfiguration IP address Subnet mask Default gateway
CLIENT OPERATING SYSTEM
34
3. Ping 127.0.0.1 to verify that the IP address is working and configured for your adapter. Press Enter. What message that you get? _______________________________________________
Exercise: Configure TCP/IP Configuration to Use a Static IP Address 1. Click Start, and then click Control Panel.
2. In the Control Panel window, click Network and Internet Connections.
3. In the Network and Internet Connections window, click Network Connections, and
then click Local Area Connection.
4. At the Local Area Right-click Local Area Connection, then click Properties.
5. Local Area Connection properties appear. Click Internet Protocol (TCP/IP), and then verify that the check box to the left of the entry is selected.
6. Click Properties. The Internet Protocol (TCP/IP) Properties dialog box appears.
7. Click Use The Following IP Address.
8. In the IP address text box, type 198.168.1.201; in the Subnet Mask text box, type
255.255.255.0.
9. Click OK to return to the Local Area Connection Properties dialog box.
10. Click Close to close the Local Area Connection Properties dialog box and return to the Network Connections window.
11. Minimize the Network Connections window.
12. Restore the command prompt.
13. At the command prompt, type ipconfig /all and press Enter.
14. Record the current TCP/IP configuration settings for your local area connection in the
following table.
15. Ping 127.0.0.1 to verify that the IP address is working and configured for your adapter.
