CHAPTER 2
Networking
Because users depend on network resources to use critical applications such as e-mail,
you must be able to diagnose common network problems quickly. Windows 7 can
diagnose many common problems automatically and includes tools that you can use to test
other conditions manually. This chapter teaches you how to configure network settings on
computers running Windows 7 and how to troubleshoot problems when they arise.
Wireless networks are becoming increasingly common, and most mobile computers
regularly connect to one or more wireless networks. Many traveling users connect to dozens
of wireless networks—some at the office, some in their homes, and some at public wireless
hotspots in coffee shops or airports.
To ensure that users can stay connected, you must understand how to configure and
troubleshoot both wired and wireless networks. This chapter teaches you how to use
network troubleshooting tools to diagnose and resolve connectivity problems, including
name resolution problems.
Exam objectives in this chapter:
■ Identify and resolve network connectivity issues.
■ Identify and resolve names resolution issues.
■ Identify and resolve wireless connectivity issues.
Lessons in this chapter:
■ Lesson 1: Troubleshooting Network Connectivity 51
■ Lesson 2: Troubleshooting Name Resolution 70
■ Lesson 3: Troubleshooting Wireless Networks 77
Before You Begin
To complete the lessons in this chapter, you should be familiar with Windows 7 and be
comfortable with the following tasks:
■ Installing Windows 7
■ Physically connecting a computer to a network
■ Configuring a wireless access point
■ Performing basic administration tasks on a Windows Server 2008 R2–based domain
controller
To complete the practices in Lesson 3, “Troubleshooting Wireless Networks,” you must
have a wireless access point and a computer that is running Windows 7 and has a wireless
network adapter.
REAL WORLD
Tony Northrup
This chapter teaches you to use a variety of different network troubleshooting
tools, including Ping, PathPing, Nslookup, and Ipconfig. The most important
troubleshooting tool, however, is the one that requires almost no training: Windows
Network Diagnostics. Windows Network Diagnostics automates the process of
diagnosing network problems, and it can even automatically resolve many problems
related to network configuration.
Automating diagnosis eliminates many aspects of human error. When I used
to troubleshoot network problems manually, I often started with a hunch.
For example, if the router had failed in the past, I might assume that the problem
was the router and attempt to ping it. If the ping failed, I’d assume that that
confirmed my hunch—however, the failed ping could also have been caused by
a failed network adapter, an IP misconfiguration, or a firewall setting. I might have
even mistyped the router’s IP address.
Sometimes, starting with a hunch can save you time. If your hunch is wrong,
however, you can waste hours trying to fi x a problem that doesn’t exist. Windows
Network Diagnostics never starts with a hunch, but it’s not wasting time, because it
performs complex diagnostics in just a few seconds. It never skips steps, forgets to
check something, or makes a typo.
In the real world, Windows Network Diagnostics should always be the first place you
start troubleshooting. You can then use the other troubleshooting tools to confirm
the problem or perform additional diagnosis if Windows Network Diagnostics
doesn’t give you a useful answer.
Lesson 1: Troubleshooting Network Connectivity
If a network adapter, network cable, switch, router, Internet connection, or server fails,
it appears to a user that he can’t connect to a network. Often, this means that he can’t do
his job, making it critical that you identify and solve the problem quickly. Because network
failures can be caused by many different components, it is important that you understand
how each component works and the tools that you can use to identify whether any
given component has failed. This lesson describes how to identify the source of network
connectivity problems and, when possible, resolve the problem.
After this lesson, you will be able to:
■ Use Windows Network Diagnostics to troubleshoot common network problems
automatically.
■ Use Ping, PathPing, PortQry, and Nslookup to troubleshoot network problems
manually.
■ Troubleshoot problems connecting to shared folders.
■ Troubleshoot an Automatic Private IP Addressing (APIPA) address.
■ Troubleshoot a name resolution problem.
■ Troubleshoot a network or application connectivity problem.
Estimated lesson time: 45 minutes
How to Use Windows Network Diagnostics
Windows 7 includes diagnostic tools that automate the process of testing for common
network problems. Windows 7 can also automatically fi x many network problems that are
configuration-related or that simply require the network adapter to be reset.
There are several ways to start Windows Network Diagnostics:
■ In the system tray, right-click the network icon and click Troubleshoot Problems,
as shown in Figure 2-1.
FIGURE 2-1 You can start Windows Network Diagnostics
from the networking icon in the system tray.
■ Open Network And Sharing Center (for example, by right-clicking the networking
icon in the system tray and then clicking Open Network And Sharing Center). On the
Network Map, click the link with an X over it (as shown in Figure 2-2).
FIGURE 2-2 Click a broken link in Network And Sharing Center to diagnose a problem.
■ Open Network And Sharing Center. Near the bottom of the right pane, click the
Troubleshoot Problems link.
■ From the Network Connections page in Control Panel, right-click a network adapter
and then click Diagnose.
■ When Windows Internet Explorer is unable to access a Web site, click the Diagnose
Connection Problems link.
■ Hold down the Windows logo key and press R to open the Run dialog box. Type
rundll32.exe ndfapi,NdfRunDllDiagnoseIncident (a case-sensitive command), and
then press Enter.
After Windows Network Diagnostics completes diagnostics, it displays a list of detected
problems. For example, Figure 2-3 shows that the computer was connected to the network
properly but that the Domain Name System (DNS) server was unavailable. An unavailable
DNS server resembles a complete connectivity failure because no computers identified
by a host name are available; however, solving the problem requires either Configuring
a different DNS server IP address or bringing the DNS server back online.
Figure 2-4 shows a problem that Windows Network Diagnostics solved: a disabled network
adapter. In this scenario, the user simply followed the wizard prompts to reenable the
network adapter.
FIGURE 2-3 Use Windows Network Diagnostics to quickly identify problems
that would be time-consuming for a person to isolate.
3. In the Actions pane, click Filter Current Log.
4. In the Filter Current Log dialog box, click the Event Sources list, and then select
Diagnostics-Networking. Click OK.
5. The Event Viewer snap-in displays a list of events generated by Windows Network
Diagnostics with detailed information about every troubleshooting session.
Network Troubleshooting Tools
If Windows Network Diagnostics does not isolate the source of the problem, Windows 7
provides many tools you can use to perform manual troubleshooting. The sections that follow
describe the most important tools. Later, this chapter will describe how to use each tool to
troubleshoot specific network problems.
Ipconfig
The network troubleshooting tool that most administrators use to begin diagnosing a problem
is the command-line tool Ipconfig. Ipconfig can be used in many different ways, which are
discussed throughout this chapter.
To view the computer’s current IP configuration quickly, run the following command:
C:\ipconfig /all
Windows IP Configuration
Host Name . . . . . . . . . . . . : WIN7
Primary Dns Suffix . . . . . . . :
Node Type . . . . . . . . . . . . : Mixed
IP Routing Enabled. . . . . . . . : No
WINS Proxy Enabled. . . . . . . . : No
Ethernet adapter Local Area Connection:
Media State . . . . . . . . . . . : Media disconnected
Connection-specific DNS Suffix . :
Description . . . . . . . . . . . : Broadcom NetXtreme 57xx Gigabit Controller
Physical Address. . . . . . . . . : 00-15-C5-07-BF-34
DHCP Enabled. . . . . . . . . . . : Yes
Autoconfiguration Enabled . . . . : Yes
Wireless LAN adapter Wireless Network Connection:
Connection-specific DNS Suffix . :
Description . . . . . . . . . . . : Intel(R) PRO/Wireless 3945ABG Network Connection
Physical Address. . . . . . . . . : 00-13-02-1E-E6-59
DHCP Enabled. . . . . . . . . . . : Yes
Autoconfiguration Enabled . . . . : Yes
IPv4 Address. . . . . . . . . . . : 192.168.1.130(Preferred)
Subnet Mask . . . . . . . . . . . : 255.255.255.0
Lease Obtained. . . . . . . . . . : Wednesday, August 05, 2009 12:48:35 PM
Lease Expires . . . . . . . . . . : Thursday, August 06, 2009 12:48:34 PM
Default Gateway . . . . . . . . . : 192.168.1.1
DHCP Server . . . . . . . . . . . : 192.168.1.1
DNS Servers . . . . . . . . . . . : 192.168.0.1
NetBIOS over Tcpip. . . . . . . . : Enabled
If you examine the sample output, you’ll notice that the Gigabit wired Ethernet controller
is disconnected. The computer is connected to a wireless network, however, and a Dynamic
Host Configuration Protocol (DHCP) server has assigned it the Internet Protocol (IP) address
192.168.1.130. The default gateway is at IP address 192.168.1.1, and the DNS server is at
IP address 192.168.0.1.
You can also use Ipconfig to update a computer’s IP configuration. If a computer has been
assigned an IP address automatically by a DHCP server (as most clients are), you can acquire
a new IPv4 address by running the following two commands:
ipconfig /release
ipconfig /renew
To acquire a new IPv6 address, run the following two commands:
ipconfig /release6
ipconfig /renew6
Ipconfig also has DNS troubleshooting capabilities, as described in Lesson 2, “Troubleshooting
Name Resolution.”
Ping
Ping is the best-known network diagnostic tool. Unfortunately, as more and more computers
and routers block Internet Control Message Protocol (ICMP) requests (ICMP is the network
protocol Ping uses), it has become less useful over time. Ping still works on most local area
networks (LANs), however.
To use Ping, open a command prompt and run the command Ping host name.
For example:
C:\>ping www.contoso.com
Pinging contoso.com [207.46.197.32] with 32 bytes of data:
Reply from 207.46.197.32: bytes=32 time=95ms TTL=105
Reply from 207.46.197.32: bytes=32 time=210ms TTL=105
Reply from 207.46.197.32: bytes=32 time=234ms TTL=105
Reply from 207.46.197.32: bytes=32 time=258ms TTL=105
Ping statistics for 207.46.197.32:
Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),
Approximate round trip times in milli-seconds:
Minimum = 95ms, Maximum = 258ms, Average = 199ms
Ping tells you several useful things. If you receive replies, you know that the network host
is turned on and connected to the network. The time, measured in milliseconds (ms), indicates
the round-trip latency between you and the remote host. Latency is the delay between
sending a packet and receiving a response, and it is caused by the time that it takes routers
to forward packets between networks and the time that signals take to traverse electrical or
fiber optic links. If the latency is greater than a second, all network communications probably
seem very slow.
Many hosts do not respond to Ping requests even though they are online. For example,
the Microsoft.com Web servers drop ICMP requests even though they are online and will
respond to Web requests, as the following sample demonstrates:
C:\>ping www.microsoft.com
Pinging lb1.www.microsoft.com [10.46.20.60] with 32 bytes of data:
Request timed out.
Request timed out.
Request timed out.
Request timed out.
Ping statistics for 10.46.20.60:
Packets: Sent = 4, Received = 0, Lost = 4 (100% loss),
You can use Ping as a very simplistic network monitoring tool if you are waiting for
a remote computer to turn off or on. To ping a host continually, use the –t parameter, as the
following example demonstrates. Ping sends requests until you press Ctrl+C to cancel the
command or you close the command prompt:
C:\>ping www.contoso.com –t
PathPing
Although Ping uses ICMP to test connectivity to a specific host, PathPing uses ICMP to test
connectivity to a remote host and all routers between you and the remote host. This can help
you identify problems in the way your network is routing traffic, such as routing loops (where
traffic crosses the same router more than once), a failed router (which might make it seem like
the entire network has failed), or poor network performance. Figure 2-5 demonstrates how
PathPing functions.
FIGURE 2-5 PathPing sends requests to every host between the client and a destination.
EXAM TIP PathPing VS. Tracert
Windows 7 still includes Tracert (pronounced Trace Route), but PathPing does everything
Tracert does and is more powerful, so you should use PathPing instead. Expect exam
questions to cover Tracert, however.
Use PathPing in the exact same way as Ping. PathPing attempts to list every router
between you and the destination (just as Tracert would). Then, PathPing spends a few
minutes calculating statistics for the entire route:
C:\>pathping www.contoso.com
Tracing route to contoso.com [10.46.196.103]over a maximum of 30 hops: 0 contoso-test
[192.168.1.207] 1 10.211.240.1 2 10.128.191.245 3 10.128.191.73
4 10.125.39.213 5 gbr1-p70.cb1ma.ip.contoso.com [10.123.40.98]
6 tbr2-p013501.cb1ma.ip.contoso.com [10.122.11.201] 7 tbr2-p012101.cgcil.ip.contoso
.com [10.122.10.106] 8 gbr4-p50.st6wa.ip.contoso.com [10.122.2.54]
9 gar1-p370.stwwa.ip.contoso.com [10.123.203.177] 10 10.127.70.6 11 10.46.33.225
12 10.46.36.210 13 10.46.155.17 14 10.46.129.51 15 10.46.196.103
Computing statistics for 625 seconds... Source to Here This Node/LinkHop
RTT Lost/Sent = Pct Lost/Sent = Pct Address 0
contoso-test [192.168.1.207] 0/ 100 = 0% | 1 50ms
1/ 100 = 1% 1/ 100 = 1% 10.211.24.1 0/ 100 = 0%
| 2 50ms 0/ 100 = 0% 0/ 100 = 0% 10.128.19.245
0/ 100 = 0% | 3 50ms 2/ 100 = 2% 2/ 100 = 2% 10.128.19.73
0/ 100 = 0% | 4 44ms 0/ 100 = 0% 0/ 100 = 0% 10.12.39.213
0/ 100 = 0% | 5 46ms 0/ 100 = 0% 0/ 100 = 0% gbr1-p70.cb1ma.ip.contoso
.com [10.12.40.98]
0/ 100 = 0% | 6 40ms 2/ 100 = 2% 2/ 100 = 2%
tbr2-p013501.cb1ma.ip.contoso.com [10.12.11.201]
0/ 100 = 0% | 7 62ms 1/ 100 = 1% 1/ 100 = 1%
tbr2-p012101.cgcil.ip.contoso.com [10.12.10.106]
0/ 100 = 0% | 8 107ms 2/ 100 = 2% 2/ 100 = 2% gbr4-p50.st6wa.ip.contoso
.com [10.12.2.54]
0/ 100 = 0% | 9 111ms 0/ 100 = 0% 0/ 100 = 0% gar1-p370.stwwa.
ip.contoso.com [10.12.203.177]
0/ 100 = 0% | 10 118ms 0/ 100 = 0% 0/ 100 = 0% 10.12.70.6
0/ 100 = 0% | 11 --- 100/ 100 =100% 100/ 100 =100% 10.46.33.225
0/ 100 = 0% | 12 --- 100/ 100 =100% 100/ 100 =100% 10.46.36.210
0/ 100 = 0% | 13 123ms 0/ 100 = 0% 0/ 100 = 0% 10.46.155.17
0/ 100 = 0% | 14 127ms 0/ 100 = 0% 0/ 100 = 0% 10.46.129.51
1/ 100 = 1% | 15 125ms 1/ 100 = 1% 0/ 100 = 0% 10.46.196.103 Trace
complete.
NOTE NETWORK LINGO
The term hop is another name for a router or gateway. Node or link are other names for
a computer or router. RTT stands for “Round Trip Time,” which is the time it takes a packet
to get from the client to the destination, plus the time for the response to be returned to
the client.
If the statistics show a single router with an extremely high latency, that node might be
causing network problems. Typically, a router with high latency increases the latency for every
router listed afterward. However, only the first router is experiencing the problem. If one
router has high latency but the routers listed afterward have low latency, the latency probably
isn’t a sign of a problem. Routers handle ICMP requests at a lower priority than other traffic,
so PathPing showing high latency isn’t always indicative of overall latency.
You can often determine from the name of the router whether it is on your internal
network, the network of your Internet service provider (ISP), or elsewhere on the Internet. If
it is on your internal network or your ISP’s network, contact your network administrator for
troubleshooting assistance. If it is somewhere else on the network, there is probably nothing
you can do but wait for the administrators of the router to solve the problem. However, if you
contact your ISP, they might be able to contact the remote ISP to ensure that they are aware
of the problem and to receive an estimate for when the problem will be solved.
To speed up the display of PathPing, use the –d command option to keep PathPing from
attempting to resolve the name of each intermediate router address.
PortQry
Ping uses ICMP packets to test whether a remote computer is connected to the network.
However, even if a computer responds to ICMP packets, it doesn’t tell you whether the
computer is running the network service that you need. For example, if you’re having
a problem downloading your e-mail, you need to test whether the mail service itself is
responding, not whether the mail server is responding to ICMP requests.
PortQry tests whether a specific network service is running on a server. To use PortQry,
open a command prompt and run the following command:
portqry –n destination –e portnumber
For example, the Hypertext Transfer Protocol (HTTP) uses TCP port 80. To test HTTP
connectivity to www.microsoft.com, type the following command at the command line:
portqry -n www.microsoft.com –e 80
This command produces output that is similar to the following example:
Querying target system called:
www.microsoft.com
Attempting to resolve name to IP address...
Name resolved to 10.209.68.190
TCP port 80 (http service): LISTENING
For a list of common port numbers, refer to the section entitled “How to Troubleshoot
Application Connectivity Problems,” later in this lesson.
Unfortunately, PortQry is not included with any version of Microsoft Windows, including
Windows 7. Instead, you must download it from Microsoft.com at http://www.microsoft.com/
downloads/details.aspx?FamilyID=89811747-C74B-4638-A2D5-AC828BDC6983. When deploying
Windows 7, consider adding PortQry to the %Windir%\System32\ folder so that it is readily
available for troubleshooting.
If you are using a computer that does not have PortQry installed, you can use the Telnet
client to test a remote service. For more information, read the section entitled “How to
Troubleshoot Application Connectivity Problems,” later in this lesson.
Nslookup
Use Nslookup to test whether your DNS server can properly resolve a host name to an IP
address. For example:
C:\>nslookup contoso.com
Server: dns.fabrikam.com
Address: 192.168.1.1:53
Non-authoritative answer:
Name: contoso.com
Addresses: 207.46.232.182, 207.46.197.32
In the previous example, the client contacted the default DNS server (192.168.1.1)
and successfully received a response indicating that contoso.com has two IP addresses:
207.46.232.182 and 207.46.197.32. This indicates that the DNS server is working correctly.
NOTE ROUND-ROBIN DNS ADDRESSING
Some host names, including contoso.com and microsoft.com, resolve to multiple IP addresses.
Your Web browser is smart enough to connect to a different address if the first address isn’t
working properly, allowing multiple Web servers with different IP addresses to respond to
requests for the same host name. This provides both scalability (the ability to handle more
simultaneous requests) and redundancy (the ability for a website to stay online if one server fails).
The following response to the same query would indicate that the DNS server could not
find an IP address for the contoso.com host name:
*** dns.fabrikam.com can’t find contoso.com: Non-existent domain
The following response indicates that no DNS server is responding:
Server: dns.fabrikam.com
Address: 192.168.1.1:53
DNS request timed out.
timeout was 2 seconds.
If the network adapter still has an APIPA address after running these commands and you
are connected to the network, the DHCP server is either offline or has determined that your
computer is not authorized to connect to the network. Bring a DHCP server online and then
restart the computer. If the network does not use a DHCP server, configure a static or alternate
IPv4 address provided by your network administrator.
Quick Check
■ How can you recognize an APIPA address?
Quick Check Answer
■ It begins with 169.254.
REAL WORLD
Tony Northrup
If you can’t get an address from the DHCP server but you do seem to be connected
to the network, try manually Configuring an IP address on the computer. First,
log on to a computer that is working properly on the network and make note
of its IP address, subnet mask, default gateway, and DNS server addresses.
Then, disconnect the computer from the network or shut it down completely.
Now, configure the computer that can’t connect to the network using the
working computer’s IP configuration. If everything works properly with the new
configuration, you know the problem is just the DHCP server and not the network
infrastructure.
After using this technique to determine whether the DHCP server is the cause of
the problem, you should immediately reconfigure the computer to act as a DHCP
client. Two computers on the same network cannot simultaneously have the same
IP address.
How to Troubleshoot Connectivity Problems
Network connectivity problems prevent any application from accessing a network resource,
whereas application connectivity problems prevent only specific applications from accessing
resources. Most network connectivity problems result from one of the following issues
(starting with the most likely):
■ Misconfigured network adapter
■ Misconfigured network hardware
■ Failed network connection
■ Faulty network cables
■ Failed network adapter
■ Failed network hardware
Application connectivity problems, however, tend to result from one of the following
issues (starting with the most likely):
■ The remote service is not running. For example, if you’re trying to control a computer
remotely, Remote Desktop might not be enabled on the remote computer.
■ The remote server has a firewall configured that is blocking that application’s
communications from the client computer.
■ A firewall between the client and server computer is blocking that application’s
communications.
■ Windows Firewall on the local computer might be configured to block the application’s
traffic.
■ The remote service has been configured to use a no default port number.
For example, Web servers typically use TCP port 80, but some administrators might
configure TCP port 81 or a different port.
The sections that follow describe how to troubleshoot network and application
connectivity problems.
How to Troubleshoot Network Connectivity Problems Manually
To identify the source of a connectivity problem without using Windows Network Diagnostics,
follow these steps and answer the questions until you are directed to a different section:
1. Click the networking notification icon in the system tray, and then click Open Network
And Sharing Center.
■ If a red X is displayed over a network link, click the link to start Windows Network
Diagnostics and follow the prompts that appear. If the red X is between the network
and the Internet, the problem is with the Internet connection and not the local
computer. Contact the network administrator for assistance.
■ If no network adapters appear, either a network adapter isn’t present, network
adapters are disabled, the hardware has failed, or the driver is not functioning.
Re-enable any disabled network adapters. If the problem persists, restart the
computer. If the network adapter is still not available, use Device Manager
(Devmgmt.msc) to diagnose the problem. If possible, update the driver by using
Microsoft Update or by checking the network adapter vendor’s Web site.
2. Can other computers connect to the same network? If not, the problem is with
the network and not the computer you’re troubleshooting. Contact the network
administrator for assistance.
3. Can you connect to other network resources? For example, if you can browse the Web
but you can’t connect to a shared folder, you are probably experiencing an application
connectivity problem. For more information, read the section entitled “How to
Troubleshoot Application Connectivity Problems,” later in this lesson.
4. Open a command prompt and run ipconfig /all. Examine the output:
■ If the computer has an IP address in the range 169.254.0.0 through 169.254.255.255,
the computer is configured to use DHCP addressing but a DHCP server was not
available. Follow the instructions in the section entitled “How to Troubleshoot an
APIPA Address,” earlier in this chapter.
■ If you have a valid IP address but do not have a default gateway or a DNS
server, the problem is caused by an invalid IP configuration. If the computer has
a DHCP-assigned IP address, run ipconfig /release and ipconfig /renew from
an administrative command prompt. If the computer has a manually configured
IP address, obtain the correct configuration from a network administrator.
■ If no network adapters are listed, the computer either lacks a network adapter or
(more likely) it does not have a valid driver installed. Use Device Manager to identify
the network adapter and then install an updated driver. If the hardware has failed,
replace the network adapter (or add a new network adapter if the network adapter
is built in).
■ If all network adapters show a Media State of Media Disconnected, the computer is
not physically connected to a network. Connect the computer to a wired or wireless
network. If you are connected to a wired network and you still see this error,
disconnect and reconnect both ends of the network cable. If the problem continues,
replace the network cable. Attempt to connect a different computer to the same
network cable; if the new computer can connect successfully, the original computer
has a failed network adapter. If neither computer can connect successfully, the
problem is with the network wiring, the network switch, or the network hub.
Replace the network hardware as necessary.
■ If all network adapters show DHCP Enabled: No in the display of the Ipconfig /all
command, the network adapter might be misconfigured. If DHCP is disabled, the
computer has a static IPv4 address, which is an unusual configuration for client
computers. Update the network adapter IPv4 configuration to Obtain An IP Address
Automatically and Obtain DNS Server Address Automatically. Then, configure the
Alternate Configuration tab of the IP Properties dialog box with the current static
IP configuration.
5. If you have a valid IP address and you can ping your default gateway, open a command
prompt and run the command “Nslookup <servername>.” If Nslookup cannot resolve
a valid name and does not display an answer similar to the following, you have a name
resolution problem. See the section entitled “How to Troubleshoot Name Resolution
Problems,” in Lesson 2.
C:\>nslookup contoso.com
Non-authoritative answer:
Name: contoso.com
Addresses: 10.46.232.182, 10.46.130.117
Those troubleshooting steps should allow you to identify the cause of most network
problems.
Quick Check
■ Which two commands would you run to get a new IP address from the DHCP
server?
Quick Check Answer
■ Ipconfig /release and Ipconfig /renew.
How to Troubleshoot Application Connectivity Problems
If one application (or network protocol) works correctly but others don’t, you are experiencing
an application connectivity issue. To troubleshoot this type of problem, follow these steps:
1. Make sure that you do not have a name resolution problem by using Nslookup to
query the server name you are trying to contact. If Nslookup cannot resolve the name,
refer to Lesson 2.
2. Often, a firewall might block your application’s communications. Before you can test
whether this is the case, you must identify the network protocol and port number used
by the application. Table 2-1 lists port numbers for common applications. If you are
not sure which port numbers your application uses, consult the application’s manual
or contact the technical support team. Often, searching the Internet for the phrase
“<application_name> port number” identifies the required port numbers. Sometimes,
administrators change port numbers to nonstandard values. If that is the case, you will
need to ask the administrator for the new port number.
TABLE 2-1 Default Port Assignments for Common Services and Tasks
| SERVICE NAME OR TASK | USER DATAGRAM PROTOCOL (UDP) | TRANSMISSION CONTROL PROTOCOL (TCP) |
| Web servers, HTTP, and Internet Information Services (IIS) | — | 80 |
| Web servers that use Hypertext Transfer Protocol Secure (HTTPS) | — | 443 |
| File Transfer Protocol (FTP) servers | | 20, 21 |
| DNS queries | 53 | 53 |
| DHCP client | | 67 |
| File and printer sharing | 137 | 139, 445 |
| Internet Relay Chat (IRC) | | 6667 |
| Incoming e-mail: Internet Mail Access Protocol (IMAP) | | 143 |
| Incoming e-mail: IMAP (Secure Sockets Layer [SSL]) | | 993 |
| Incoming e-mail: Post Office Protocol 3 (POP3) | | 110 |
| Incoming e-mail: POP3 (SSL) | | 995 |
| Outgoing e-mail: Simple Mail Transfer Protocol (SMTP) | | 25 |
| Connecting to an Active Directory Domain Services (AD DS) domain controller | 389, 53, 88 | 135, 389, 636, 3268, 3269, 53, 88, 445 |
| Network Management: Simple Network Management Protocol (SNMP) | 161, 162 | |
| SQL Server | | 1433 |
| Telnet | | 23 |
| Terminal Server, Remote Desktop, and Remote Assistance | | 3389 |
| Virtual Machine Remote Control (VMRC) client for Microsoft Virtual Server 2005 R2 | | 5900 |
3. After you identify the port numbers required by your application, test whether you
can connect manually to that port on the server. If it is a TCP port, you can use either
PortQry or Telnet. To test a TCP port with Telnet (which is available if you turn on the
Telnet Client feature by using the Turn Windows Features On Or Off tool in Control
Panel), run the following command:
Telnet <hostname_or_address> <TCP_port>
For example, to determine whether you can connect to the Web server at
www.microsoft.com (which uses port 80), you would run the following command:
Telnet www.microsoft.com 80
If the command prompt clears or if you receive text from the remote service, you
successfully established a connection, which means you do not have an application
connectivity problem. Instead, you might have an authentication problem or there might be
a problem with the client or server software.
If Telnet displays “Could not open connection to the host,” this verifies that you do indeed
have an application connectivity issue. Either the server is offline or a misconfigured firewall is
blocking the application’s network traffic. Follow these steps to continue troubleshooting the
problem:
1. Verify that the server is online by connecting to a different service running on the
same server. For example, if you are attempting to connect to a Web server and you
know that the server has File Sharing enabled, attempt to connect to a shared folder.
If you can connect to a different service, the problem is almost certainly a firewall
configuration problem on the server. If you don’t know that another service is running
on the server, contact the server administrator to verify that it’s running.
2. Attempt to connect from different computers on the same and different subnets.
If you can connect from a computer on the same subnet, the problem is caused by
a firewall or application configuration problem on your computer. Verify that a firewall
exception is created either for your application or for the port numbers it uses.
(For more information, see Chapter 5, “Protecting Client Systems.”) If you can connect
from a client computer on a different subnet but not from the same subnet, a firewall
on the network or on the server is probably filtering traffic from your client network.
Contact a network administrator for assistance.
PRACTICE Troubleshoot a Connectivity Problem
In this practice, you troubleshoot two common network problems.
EXERCISE 1 Solve a Network Problem Automatically
In this exercise, you run a batch fi le to generate a networking problem, and then you
troubleshoot it using Windows Network Diagnostics. This practice simulates a network
problem on your computer. Before you run it, verify that you are connected to the network
and can access network resources and be prepared to be disconnected from the network.
Do not perform this exercise on a server or other computer that would affect users if it went
offline.
1. After installing the practice fi les from the companion CD, browse to the installation
folder on your computer. Then, right-click that fi le on your desktop and click Run As
Administrator.
2. You can ignore the command window that appears; the batch fi le just simulates
a networking failure. Now, you will troubleshoot the problem.
3. Open Internet Explorer and attempt to view a Web site. Notice that the Internet is not
available.
4. Right-click the networking icon in the system tray (which should now have a red X over
it) and then click Open Network And Sharing Center.
5. Network And Sharing Center appears and displays the Network Map.
6. Click the red X on the network map, which indicates that you are not connected to
the LAN.
7. Follow the troubleshooting instructions that appear and try the repairs as an
administrator when prompted. When Windows Network Diagnostics identifies the
problem, click the solution that is presented to solve it.
Windows Network Diagnostics fixes the network problem. Notice that the steps
were simple enough that a user could have followed them. Although this exercise
demonstrated the use of Network And Sharing Center to start Windows Network
Diagnostics, you also could have clicked Diagnose Connection Problems from Internet
Explorer or right-clicked the networking icon and then clicked Troubleshoot Problems.
EXERCISE 2 Solve a Network Problem Manually
In this exercise, you run a batch fi le to generate a networking problem, and then you
troubleshoot it using manual network troubleshooting tools. This practice simulates
a network problem on your computer. Before you run it, verify that you are connected to the
network and can access network resources and be prepared to be disconnected from the
network. Do not perform this exercise on a server or other computer that would affect users
if it went offline.
1. On the companion CD, browse to the folder for this chapter. Copy the Chapter2-
Lesson1-Exercise2.bat fi le to your desktop. Right-click that fi le on your desktop and
click Run As Administrator.
You can ignore the command window that appears; the batch fi le just simulates
a networking failure. Now, you troubleshoot the problem.
2. Open a command prompt and run the command ipconfig /all.
3. Examine the output.
Notice that no network adapters appear. To investigate the problem further, you
should view the network adapter configuration.
4. Click the networking notification icon in the system tray (which should now have a red
X over it), and then click Open Network And Sharing Center.
5. In the left pane, click Change Adapter Settings.
6. Notice that the network adapters are disabled. To re-enable each network adapter,
right-click it, and then click Enable.
Wait a few moments for the network adapter to retrieve a new IP address. Then, verify
that you can connect to the network.
Lesson Summary
■ Windows Network Diagnostics can identify many common network problems
automatically. Windows Network Diagnostics can be started from many places, and it
often prompts the user to run it when a network problem is detected.
■ Use Ping to test connectivity to a remote host. PathPing functions similarly but also
lists the routers between you and the remote host. Use PortQry or Telnet to determine
whether a remote server is listening for connections on a specific port. Use Nslookup
to troubleshoot DNS name resolution problems.
■ You can troubleshoot problems connecting to shared folders from either the client
or the server. Most often the problem is related to insufficient privileges. However,
the server might be offline, Windows Firewall might be blocking the connection, or
a network firewall might be filtering the network traffic.
■ APIPA addresses are in the range 169.254.0.0 through 169.254.255.255. If a computer
is assigned one of these addresses, it means that the computer is configured to receive
a DHCP address but a DHCP server was not available. You can resolve this problem by
verifying that a DHCP server is online and then refreshing the DHCP configuration by
running ipconfig /release and then ipconfig /renew.
■ Connectivity problems can be caused by either the network or the application.
Network connectivity problems prevent any traffic from being sent. Application
connectivity problems block just the application’s specific traffic. Typically, application
connectivity problems occur because a Windows Firewall exception was not created
on the server or a network firewall is blocking the application’s communications.
Lesson Review
You can use the following questions to test your knowledge of the information in Lesson 1,
“Troubleshooting Network Connectivity.” The questions are also available on the companion
CD if you prefer to review them in electronic form.
NOTE ANSWERS
Answers to these questions and explanations of why each answer choice is correct or incorrect
are located in the “Answers” section at the end of the book.
1. Microsoft Office Outlook gives you an error message when you attempt to download
your mail. You verify that you can connect to other computers on the network. Which
tools could you use to determine whether the mail server is responding to incoming
e-mail requests? (Choose all that apply.)
A. Ping
B. Telnet
C. PortQry
D. PathPing
2. Which of the following IP addresses would indicate that a client computer could not
retrieve an IP address from a DHCP server and did not have an alternate configuration?
A. 10.24.68.20
B. 127.0.0.1
C. 192.168.22.93
D. 169.254.43.98
3. You are unable to connect to a server on the Internet. However, you can still reach
servers on the intranet. You need to determine whether your local router has failed, if
your ISP is experiencing problems, or if the problem is with a different ISP. Which tools
should you use to troubleshoot the problem most efficiently? (Choose all that apply.)
A. Nslookup
No hay comentarios:
Publicar un comentario