Exam Essentials - Network + Chapter 4

Exam Essentials
Know how to describe and use the troubleshooting information and statistics that arp, nbtstat, and netstat provide for you. The arp utility shows whether an IP address is being resolved to your MAC address (or someone else’s in case of conflicts). The netstat utility produces TCP/IP statistics, and nbtstat produces NetBIOS over TCP/IP statistics.

Know how to diagnose a network by using TCP/IP’s troubleshooting commands.
 Ping echoes back if a machine is alive and active on a network. Tracert shows the path that the ping packets take from source to target. And Telnet enables a user to participate in a remote textbased session.
Know what the tracert utility does. The tracert utility finds the route from your computer to any computer on a network.

Know what the ping utility does. Ping determines if a particular IP host is responding.

Know what the ftp utility does. The ftp utility allows you to reliably download and upload files from and to an FTP server across the Internet.

Know what the ipconfig and ifconfig utilities do. Ipconfig displays TCP/IP configuration
information for Windows NT and later operating systems. The ifconfig utility performs
a similar function in UNIX environments, in addition to performing certain interface configuration
tasks.
Know what the winipcfg utility does. Winipcfg displays TCP/IP configuration information for Windows 95/98.

Know what the nslookup and dig utilities do. Nslookup and dig allow you to look up DNS resolution information.

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Summary - Network + Chapter

Summary
In this chapter you learned about many of the utilities for using and troubleshooting TCP/IP. These utilities include tracert, ping, arp, netstat, nbtstat, ipconfig, winipcfg, ifconfig, dig, and nslookup. You also learned how these utilities are used, including their
various options and switches and how they affect the use of these utilities. Finally, you learned about how these utilities work within the TCP/IP suite.

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Using the nslookup Utility

Using the nslookup Utility

Whenever you are configuring a server or workstation to connect to the Internet, you will always have to configure DNS if you want name resolution to happen (i.e., if you want to be able to type www.sybex.com instead of an IP address). When configuring DNS, it is very advantageous to be able to test what IP address DNS is returning to ensure that it is working properly. The nslookup utility allows you to query a name server and quickly find out which name

resolves to which IP address.

NOTE:

The UNIX dig (short for domain information groper) utility does the exact same thing as nslookup. It is primarily a command-line utility that allows you to perform a single DNS lookup for a specific entity, but it may also be operated in batch mode for a series of lookups. While detailed information on this command is beyond the scope of this study guide, more information can be found on the Web by searching for “unix dig”.

The nslookup utility comes with Windows NT and later, as well as most versions of UNIX and Linux. It did not, however, come with Windows 95/98. You can run it from a Windows
command prompt. Once you are at the command prompt, you can start the nslookup utility by simply typing nslookup and pressing Enter. Once you’re inside this utility, the command prompt will change from something similar to C:\> sign to a shorter > sign. It will also display the name and IP address of the default DNS server you will be querying (you can change it, if necessary). Once here, you can start using nslookup. The following output shows a sample of the display after the nslookup command has been entered at the C:\> prompt.

Microsoft Windows 2000 [Version 5.00.2195]
(C) Copyright 1985-2000 Microsoft Corp.
C:\>nslookup
Default Server: ns.company.com
Address: 10.89.155.68
>

The primary job of nslookup is to tell you the many different features of a particular domain name, the name servers that serve it, and how they are configured. For example, you can simply

type in a domain name at the > prompt, like so:


>sybex.com

The nslookup utility would return this information:

Server: ns.company.com
Address: 10.89.155.68
Non-authoritative answer:
name: sybex.com

address: 10.0.0.1

This tells you that the server that returned the information was not responsible (authoritative) for the zone information of the domain for which you requested an address and that the name
server for the domain sybex.com is located at the IP address 10.0.0.1. This means that when your computer wants to talk to www.sybex.com, it must talk to the name server at 10.0.0.1 to
find out the IP address of the host called www on the sybex.com domain. You can also ask nslookup for other information by setting a different option within nslookup. Just type set option at the > prompt and replace option with the actual option you

want to use. Table 4.7 gives some of the common options and their uses.

TABLE 4 . 7 The nslookup Options and Their Uses

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Using the Telnet Utility

Using the Telnet Utility

Telnet is an acronym formed from Terminal EmuLation for NETworks. It was originally developed to open terminal sessions from remote UNIX workstations to UNIX servers. Although still
used for that purpose, it has evolved into a troubleshooting tool. Figure 4.12 shows the basic Telnet interface as it is being used to start a terminal session on a remote UNIX host.

FIGURE 4 . 1 2 The Telnet utility

In today’s Windows environments, Telnet is a basic command-line tool for testing TCP connections. You can Telnet to any TCP port to see if it is responding, which is especially useful when checking SMTP and HTTP (Web) ports. If you’ll remember from Chapter 3, each upperlayer service in a TCP stack has a number for its address. Each network service that uses a particular address will respond to a TCP request on this port (if the defaults are used). Table 4.6 lists the most commonly referenced port numbers and their associated services.

TABLE 4 . 6 TCP Port Numbers and Services

NOTE:

This list is by no means comprehensive. For a complete list, go to www.iana.org/assignments/port-numbers.

To find out if a TCP service is responding, follow these steps:

1. Choose Start Run.
2. Type Telnet and click OK to open the Telnet utility.

3. At the prompt, enter a question mark (?) to display the valid commands for this interface.

4. At the prompt, type open and the IP address or DNS host name of the device running the TCP service to which you want to connect, followed by the TCP port number (one from

Table 4.6, for instance). 

For example, to find out if the Sybex web server is responding to TCP port 80 (its default port), enter the IP address or DNS host name of the server (www.sybex.com, in this case)

followed by the TCP port number (80, in this case).

NOTE:

If you successfully connect to the web server, you won’t be notified that this is the case. If the web server doesn’t respond, you’ll receive a Connect Failed message.

5.If the procedure was successful, you can simply close the Telnet window or key in Ctrl+] to return to the Telnet prompt. 

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Using the tracert Utility

Using the tracert Utility

Have you ever wondered where the packets go when you send them over the Internet? The TCP/ IP traceroute (tracert) command-line utility will show you every router interface a TCP/IP
packet passes through on its way to a destination. To usetracert, at a Windows command prompt, type tracert, a space, and the DNS name or IP address of the host for which you want to find the route. The tracert utility responds with a list of all the DNS names and IP addresses of the routers that the packet is passing through on
its way. Additionally, tracert indicates the time it takes for each attempt. Figure 4.11 shows sample tracert output from a workstation connected to an ISP (Corporate Communications, in
Fargo, North Dakota, in this case) in the search engine Yahoo!.

FIGURE 4 . 1 1 Sample tracert output

As you can see, the packet bounces through several routers before arriving at its destination. This utility is useful if you are having problems reaching a web server on the Internet and you want to know if a WAN link is down or if the server just isn’t responding. Figure 4.11 shows that every router is up and is, in fact, responding. The asterisk indicates that the attempt for that router took longer than the default time-out value. This usually means that either the router is extremely busy or that particular link is slow. You can use tracert to ascertain how many hops a particular host is from your workstation. This is useful in determining how fast a link should be. Usually if a host is only a couple of hops away, access should be relatively quick.

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Using the ifconfig Utility

Using the ifconfig Utility
There is a utility in Linux/UNIX that shows information similar to what ipconfig shows. This utilityis called ifconfig (short for “interface configuration”). Although ipconfig and ifconfig show similar information, there are major differences between these two utilities. The ipconfig utility is used mainly to view TCP/IP configuration for a computer. You can use ifconfig to do the
same thing, but ifconfig can also be used to configure a protocol or a particular network interface. The general syntax of the ifconfig command is as follows:

ifconfig interface [address [parameters]]

The interface parameter is the UNIX name of the interface, such as eth0. If the optional address parameter is specified, the ifconfig command sets the IP address for the interface to
the address specified. When the ifconfig command is used by itself with no parameters, all configured interfaces are reported on. If only the interface name is specified, output similar to
the following is produced:

The output shows that the eth0 interface is a 10Mbps Ethernet interface. The interface’s MAC and IP address information is displayed in this output as well. The third line of the output begins

by listing the state of the various flags an interface can have. The optional parameters field at the end of the ifconfig command can be used to change the state of these flags. The MTU and metric fields are used in making routing decisions, just as they would be used in any router. The values on the RX (receive) and TX (transmit) lines represent, in order, the number of packets that were transmitted or received without errors, how many packets were transmitted or

received with errors, how many packets were dropped due to insufficient buffer space, and how many packets were lost due to the packets overrunning the capacity of the kernel to process

them. Often the receive value will be higher than the transmit value for these last two properties because transmitted packets can be controlled much more easily than inbound packets.

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Using the ipconfig Utility

Using the ipconfig Utility

Because Windows NT was designed to be UNIX compatible, Windows NT (as well as its later incarnations, including Windows 2000 Server and Windows Server 2003) and UNIX have several
functions and utilities in common. You can use many UNIX command-line utilities at the command prompt of Windows NT and later operating systems, including these:

•  ftp
• ping
• tracert
• ipconfig

The Windows utility ipconfig does roughly the same job as its Windows 95/98 counterpart, winipcfg. With Windows ipconfig, however, the display is command-line based.

NOTE:

You can also use the ipconfig utility in Windows 98, with slightly diminished features. winipcfg still remains the most useful of the two utilities in Windows 98.

1.Choose Start Programs Accessories Command Prompt to display the command prompt.

2. Type ipconfig, which produces output similar to the following:

C:>ipconfig 

Windows 2000 IP Configuration
Ethernet adapter E100B1:

Connection-specific DNS Suffix . :IP Address. . . . . . .  : 192.168.1.101Subnet Mask . .  . . . . : 255.255.255.0Default Gateway . .  . . : 192.168.1.1

C:\>


As you can see, this output is similar to the information in the Windows 95/98 IP Configuration dialog box except that the MAC address is not listed, although with the /all switch you can obtain that as well.

Only four switches can be used with the ipconfig command. Table 4.5 lists and describes all four switches, and the output that follows Table 4.5 shows the results of using the /all switch with ipconfig.

TABLE 4 . 5 ipconfig Switches

The following shows sample output produced by using the ipconfig /all switch:

C:\>ipconfig/all

Windows 2000 IP Configuration

Ethernet adapter Wireless-G Notebook Adapter:

TIP:

Because Windows servers can (and often do) have more than one TCP/IP interface, you can specify which interface you want to view statistics for by placing its address on the command line with the switches. If you don’t specify, ipconfig displays information for all interfaces.

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Using the winipcfg Utility

Using the winipcfg Utility

The IP configuration utility for Windows 95/98 is winipcfg. You use it to display the current TCP/IP configuration on a Windows 95/98 workstation. Follow these two steps to display the IP configuration information using winipcfg 

1. Choose Start Run, type winipcfg, and click OK to display the IP Configuration dialog box.

Click the down arrow to choose the network interface for which you want to view statistics.The screen in the graphic above shows this information for the Intel EtherExpress.

2- To display more detailed configuration information, click the More Info button to open the

IP Configuration dialog box shown here.

NOTE:

Even thought ifconfig is not a Windows utility, it is a TCP/IP configuration utility and it naturally fits here. Its use is very similar to the other Windows configuration utilities.

TIP:

If you are using DHCP to get IP address information, click the Release All button to remove all information obtained from a DHCP server (including an IP address). Click the Renew All button to release all DHCP information andrequest new TCP/IP configuration information.

The top of this screen shows the DNS name of the machine and the IP address of the DNS server that this workstation is using. Below that are several lines of NetBIOS over TCP/IP information.
The bottom section contains the same information shown in the first screen but includes such additional information as the addresses of the DHCP and WINS servers (if present) and the lease information (how long the DHCP information is current) for the addresses obtained from a DHCP server.

The winipcfg utility comes in handy when you’re resolving TCP/IP address conflicts and configuring a workstation. For example, if this workstation is experiencing duplicate IP address errors, you can run winipcfg to determine the IP address of this station. Also, if the address was obtained from a DHCP server, you can release it and obtain a new IP address by clicking the Renew All button.

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Using winipcfg, ipconfig, and ifconfig

Using winipcfg, ipconfig, and ifconfig

Of all the TCP/IP utilities that come with Windows, the IP configuration utilities are probably the most overlooked. These utilities display the current configuration of TCP/IP on that workstation, including the current IP address, DNS configuration, WINS configuration, and default gateway.

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