Troubleshooting Connections Using Ping and PathPing
Ping is a tool that
helps to verify IP-level connectivity; PathPing is a tool that detects
packet loss over multiple-hop trips. When troubleshooting, the Ping
command is used to send an Internet Control Message Protocol (ICMP) echo
request to a target host name or IP address. Use Ping whenever you want
to verify that a host computer can send IP packets to a destination
host. You can also use the Ping tool to locate remote hardware problems
and incompatible configurations.
When troubleshooting network connectivity, use the Ping command to perform the following sequence of tasks.
Note The
first two steps of the following sequence are already performed by the
Ipconfig /all command and Netdiag. (Network Diagnostics automatically
performs only the second step. If Network Diagnostics reports that this
self-ping test has failed, you can perform the first step manually.) |
1. | Ping
the loopback address to verify that TCP/IP is installed and configured
correctly on the local computer. To perform this step, enter ping 127.0.0.1 at a command prompt.
If the loopback step fails, the IP stack is not responding. This
problem might be occurring because the TCP drivers are corrupted, the
network adapter might not be working, or another service might be
interfering with IP.
| 2. | Ping the IP address of the local computer to verify that an address has been added correctly. To perform this step, enter ping <IP address of local host> at a command prompt.
| 3. | Ping
the IP address of the default gateway. This step verifies that the
default gateway is reachable and that the local host can communicate
with another host on the network. To perform this step, enter ping <IP address of default gateway> at a command prompt.
| 4. | Ping
the IP address of a remote host located beyond the default gateway.
This step verifies that you can communicate with hosts outside your
local network segment. To perform this step, enter ping <IP address of remote host> at a command prompt.
| 5. | Ping
the host name of a remote host to verify that you can resolve remote
host names. To perform this step, enter ping <host name of remote
host> at a command prompt.
| 6. | Run
a PathPing analysis to a remote host to determine which (if any)
routers on the way to the destination are malfunctioning. To perform
this step, enter pathping <IP address of remote host> at a command
prompt.
|
Note To
perform this last step more quickly, you can substitute the Tracert
utility for the PathPing utility. Tracert reveals breaks in connectivity
but does not provide statistics about router performance. Tracert is
described in more detail in the following section. |
Ping uses host name
resolution to resolve a computer name to an IP address, so if pinging
succeeds by address, but fails by name, the problem lies in host name
resolution, not network connectivity.
If you cannot ping successfully at any point, check to make sure the following are true:
The local computer’s IP address and subnet mask are correctly configured. A
default gateway is configured and the link between the host and the
default gateway is operational. For troubleshooting purposes, make sure
only one default gateway is configured.
Note If
the remote system being pinged is across a high-delay link such as a
satellite link, responses might take longer to be returned. You can use
the –w switch to specify a longer time-out. For example, the command ping -w 2000 172.16.48.10 waits 2 seconds before timing out. (The default setting is 1 second, expressed as 1000 milliseconds.) |
Troubleshooting with Tracert
Tracert is a
route-tracing utility that allows you to track the path of a forwarded
packet from router to router for up to 30 hops. Tracert works by sending
ICMP echo requests to an IP address, while incrementing the Time to
Live (TTL) field in the IP header, starting at 1, and analyzing the ICMP
errors that are returned. Tracert prints out an ordered list of the
routers in the path that returned these error messages. In the following
example, Tracert is used to trace the path from the local computer to a
remote computer named www.contoso.com:
C:\>tracert WWW.contoso.com
Tracing route to WWW.contoso.com [10.102.252.1]
over a maximum of 30 hops:
1 300 ms 281 ms 280 ms roto.contoso.com [10.181.164.100]
2 300 ms 301 ms 310 ms sl-stk-1-S12-T1.contoso.com [10.228.192.65]
3 300 ms 311 ms 320 ms sl-stk-5-F0/0.contoso.com [10.228.40.5]
4 380 ms 311 ms 340 ms icm-fix-w-H2/0-T3.contoso.com [10.228.10.22]
5 310 ms 301 ms 320 ms arc-nas-gw.arc.contoso.com [10.203.230.3]
6 300 ms 321 ms 320 ms n254-ed-cisco7010.contoso.com [10.102.64.254]
7 360 ms 361 ms 371 ms WWW.contoso.com [10.102.252.1]
Tip You
need to know the difference between Tracert and PathPing on the exam.
Use Tracert to quickly determine where a break occurs in the path of
connectivity to a remote location. PathPing is more useful when you have
connectivity to a site but are experiencing erratic packet loss or high
delay. In these cases, PathPing tells you exactly where packet loss is
occurring. |
Troubleshooting Using the ARP Tool
Network traffic
sometimes fails because a router’s proxy ARP request returns the wrong
address. If you can ping both the loopback address and your own IP
address, but you cannot ping a computer on the local subnet, the next
step is to check the ARP cache for errors.
The ARP command is
useful for viewing the ARP cache. If two hosts on the same subnet cannot
ping each other successfully, try running the ARP command with the –a
switch on each computer to see whether the computers have the correct
MAC addresses listed for each other. To determine a host’s MAC address,
you can use the Ipconfig /all command or the Getmac command. Then use
the ARP command with the -d switch to delete any entry that might be
incorrect. Add entries by using ARP with the –s switch.
If you cannot ping a computer
on a local subnet by IP address, and the ARP –a command reveals no
errors in hardware address mappings, you should investigate for errors
in the physical media, such as LAN cards, hubs, and cables.
Practice: Running Network Diagnostics and Netdiag
In this practice, you run both Network Diagnostics and the Netdiag utility. You then save the output of these tests to files.
Exercise 1: Running Network Diagnostics
In this exercise, you save the output from the Network Diagnostics tool to an HTML file.
1. | Log on to Computer1 as Administrator.
| 2. | Click Start, and then click Help And Support.
The Help And Support Center window opens.
| 3. | Under the Support Tasks list on the right side of the Help And Support Center window, click Tools.
| 4. | In
the Tools list on the left side of the Help And Support Center window,
expand Help And Support Center Tools, and then click Network
Diagnostics.
The Network Diagnostics tool appears on the right side of the Help And Support Center window.
| 5. | Click the Scan Your System button.
Information loads for a few seconds, and then three headings of
status information are displayed: Internet Service, Computer
Information, and Modems And Network Adapters.
| 6. | Expand all of the categories by clicking the plus symbols under them.
All of the information trees under each heading expand, revealing the full results of the tests just run.
| 7. | Take a few moments to browse the information available in the expanded trees.
| 8. | In the Network Diagnostics window, click the Set Scanning Options button.
Below the Options heading, the Actions area and the Categories area are shown.
| 9. | Under the Actions area, select the Verbose check box.
| 10. | In
the Categories area, clear the following check boxes: Mail Service,
News Service, Internet Proxy Server, Computer Information, Operating
System, and Windows Version.
Only Modems, Network Clients, and Adapters should now be selected.
| 11. | In the Network Diagnostics window, click the Scan Your System button to begin gathering information.
When the tests have completed, the Network Diagnostics window
reveals three sets of information under a single heading: Modems And
Network Adapters.
| 12. | In the Network Diagnostics window, click the Save To File button to save to a file the results of the test just run.
A message indicates that the file just created has been saved to the desktop and to another specified location.
| 13. | Click OK to close the message.
| 14. | Next to the Save To File button in the Network Diagnostics window, click Show Saved Files.
A folder opens revealing one location of the new file.
| 15. | On the Windows Quick Launch toolbar, click Show Desktop.
Another copy of the Hypertext Markup Language (HTML) file created by Network Diagnostics is visible on the desktop.
| 16. | Cut and paste this document to the My Documents folder.
| 17. | Close any remaining open windows.
|
Exercise 2: Installing Windows Support Tools
Before beginning this exercise, insert the Windows Server 2003 installation CD-ROM into the CD-ROM drive on Computer1.
1. | While you are logged on to Computer1 as Administrator, browse the Windows Server 2003 CD to the \Support\Tools folder.
| 2. | In the Tools folder, double-click Suptools.msi.
The Windows Support Tools Setup Wizard opens.
| 3. | Click Next.
The End User License Agreement page appears.
| 4. | Click the I Agree option, and then click Next.
The User Information page appears.
| 5. | In the Name text box and the Organization text box, enter your name and organization, and click Next.
The Destination Directory page appears.
| 6. | Leave the default install path, and click Install Now.
After installation is complete, the Completing The Windows Support Tools Setup Wizard page appears.
| 7. | Click Finish to exit the wizard.
|
Exercise 3: Running Netdiag from Across the Network
In this exercise, you use the Telnet utility to connect to Computer1. You then run the Netdiag utility from the Telnet prompt.
1. | While
you are logged on to Computer1 as Administrator, open the Services
console by clicking the Start button, selecting Administrative Tools,
and then clicking Services.
The Services console opens.
| 2. | In the right pane of the Services console, select Telnet from the list of services.
Note that the Status field is blank for Telnet service.
| 3. | Start
the Telnet service. One way to accomplish this task is to double-click
the Telnet icon, select Manual from the Startup Type drop-down list box,
click Apply, click Start, and then click OK.
The Service Control status box appears while the Telnet service
is starting. It disappears when the service has started successfully. In
the Services console, the Status field for the Telnet service now
contains the word Started.
| 4. | Close the Services console.
| 5. | Log on to Computer2 as Administrator.
| 6. | On Computer2, open a command prompt and enter telnet computer1.
You will be warned about sending your password to a remote computer.
| 7. | Press y, and then press Enter.
If you have assigned the Administrator account the same password
on Computer2 as on Computer1, you will receive a Welcome message and a
command prompt from Telnet Server. If you have assigned the two
Administrator accounts separate passwords, you must enter the
Administrator credentials for Computer1 before you receive this message
and command prompt.
| 8. | After you have received the Welcome message, type netdiag at the Telnet command prompt, and then press Enter.
Information gathers for a few moments, and then the output of
the Netdiag utility appears at the command prompt. This utility has been
run on Computer1.
| 9. | Briefly review the Netdiag output.
| 10. | At the Telnet command prompt, type cd my documents, and then press Enter.
The directory on Computer1 from which you are executing commands changes.
| 11. | At the Telnet prompt, type netdiag>NetdiagOutput.txt, and then press Enter.
A copy of the Netdiag output is saved to the My Documents folder on Computer1.
| 12. | At the Telnet prompt, type netdiag /v >VerboseNetdiagOutput.txt, and then press Enter.
A copy of the verbose Netdiag output is saved to the My Documents folder on Computer1.
| 13. | Switch back to Computer1 and open the My Documents folder.
| 14. | Open NetdiagOutput.txt, and then open VerboseNetdiagOutput.txt.
| 15. | Take a minute to compare the output from these two modes of the Netdiag utility.
| 16. | In
the My Documents folder, use the shortcut to the NetDiag folder to open
the HTML file that you created and saved through Network Diagnostics.
| 17. | Take a minute to compare the information in this file with the information in the two files generated from the Netdiag utility.
| 18. | Close all open windows on Computer1 and Computer2.
| 19. | Log off Computer1 and Computer2. |
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