BASIC TROUBLESHOOTING FOR TCP/IP N/W CONNECTION:

This article provides basic information about how to diagnose and test Transmission Control Protocol/Internet Protocol (TCP/IP) or NetBIOS network configurations. This article also describes the use of the most common diagnostic tools along with basic network analysis techniques.

If a computer is unable to connect to a network it may be necessary to troubleshoot the network.

Many times the network problems may be acuter TCP/IP settings. Following is the basic checklist to identify and troubleshoot the basic networking errors.

REASONS:

• ·        Network card not connected properly.
• ·        Bad network card drivers or software settings.
• ·        Firewall preventing computers from seeing each other.
• ·        Connection related issues.
• ·        Bad network hardware.

SOLUTION:

• ·        Make sure you have the same IP scheme (e.g. 192.168.0.x).

• Make sure you have the same Subnet Mask, Gateway, and DNS IP addresses

• Make sure you can ping the other computers by IP ADDRESS

• Make sure you can ping the other computers by NAME

• Make sure you have the same workgroup name (watch for trailing spaces)

• For troubleshooting purposes, uninstall any 3rd party firewall software and  turn off XP's built in one. You can always add more complexity after you get it working.

• With Windows2000, XP and Vista, make sure you have the same username and password as the person logging onto the other computers. The default setting for all but the Home Versions is to require a password for network access.

• Basically keep things simple. Remove any unnecessary firewalls, protocols or other configurations the complicate the troubleshooting process. You can add them back in later after you get things working.

STEPS AS FLLOWED:

1. First of all you should learn what stopped working server or client computer also see if the outage affecting the other computers or only one.

2. If you server stopped working you should inform the users of the server and you should start working on fixing the error.

3. If a single client computer stopped working or disconnected from the network, ask the user of that computer that what recent changes cause the server to stop working such as newly installed software or games, service packs, internet software, new hardware or any other thing.

4. Check the physical network connectivity. The most network problems arise due to the physical layers failure.

5. Check all the network cable connections. You can start at the NIC and check if the green light is blinking then check the hub and see if the computer is getting the link across the cable.

6. Get a cable tester to check the connectivity of the cables.

7. Finally start pinging the network both Windows and Linux have the PING command. You can use ping command in this way start > Run > cmd > type "ping" then IP address of the other computer.

HOW TO TROUBLESHOOT CONNECTIVITY PROBLEMS:

1. Use the ping command to test the basic connectivity. By using the ping command you can isolate network hardware problems and incompatible configurations. By using the path ping you can detect packet loss.

2. If you want to see the Ping's statistics then you ping -t command and press enter to continue and if you want to stop then press CTRL+BREAKTo watch Ping statistics, use the ping -t command. To see statistics and continue, press CTRL+BREAK. To stop, press CTRL+C.

3. If you remote system is across the delay link, such as satellite link responses may take longer.

4. Check the event logs for network card and other hardware and software configurations and connectivity related entries.

5. Check whether the NIC card is on the Microsoft Hardware Compatibility List (HCL).

6. Check other computers that use the same gateway and are plugged into the same hub or switch and if these computers do not show any network connectivity problem then the problem is on the only one computer.

7. Contact the vendor of each NIC and motherboard and update the BIOS.

8. Replace the network adapter of the system with the good configured system and see if the same Error arise again.

ISSUES IN NETWORK CONNECTIVITY:

IF A COMPUTER IS UNABLE TO CONNECT TO A NETWORK OR SEE OTHER COMPUTERS IN A NETWORK IT MAY BE NECESSARY TO TROUBLESHOOT THE NETWORK. DUE TO THE FOLLOWING REASONS YOUR NETWORK MAY NOT WORK.

•  ·        Network card not connected properly
• ·        Bad NIC card drive's settings
• ·        Firewall preventing computers from seeing each other.
• ·        Connection related issues.
• ·        Bad network hardware.

SOLUTION:

Because of the large variety of the network configurations, setup, software, hardware operating systems etc not all the information may apply to your network or operating system. First of all verify that the network cable of each computer is properly connected, one end to the NIC card, which is plugged into the computer and one end to the Hub or switch. Ensure that the green light is blinking on the NIC, this shows that the NIC is either receiving or sending the data. On the other hand if the card does not have any lights or has orange or red lights, then is possible that either the NIC adapter is bad or not connected properly.

Make sure that the cables are properly connected to the hub or swtich. Make sure that the newly installed NIC adapter is not conflicting with the other NIC cards on the network and a unique IP address is assigned to each NIC card. If there is some conflict then the device manager may identify the conflicting card. Furthermore, make sure that the NIC is capable of pinging or seeing itself by the ping command. If you are on the TCP/IP network, make sure that the correct protocols are installed. If you are using a firewall, ensure all the ports required are open. While troubleshooting you can close the firewall program so that they there should not occur any conflict.

TCP/IP CONFIGURAITONS CHECKING:

The first step in the troubleshooting process is to check the TCP/IP settings. You can check it by using the IPCONFIG/All command on the command prompt. You will see the configuration results. If you see a blank configuration for a card this means then the card is not assigned any IP address. You can assign the IP address manually or via DHCP server. If you are using the DHCP server for assigning the IP addresses then you can use the following commands to get and release the IP address.

C:\> IPCONFIG/RELEASE

C:\> IPCONFIG/RENEW

C:\> IPCONFIG/ALL

If the computer is still unalbe to obtain an IP address, then there are several things that can causing this problem such as bad network cable or NIC card, DHCP server might have assigned all the IP addresses from its pool, misconfigured TCP/IP settings, incorrect user name and password. You can try to add a new well configured machine to the replace the malfunctioning machine to see if the new machine is working with its settings. Also see if the driver of the NIC is properly installed or not. In case of driver's problem go to the vendor's website and install a new exact driver for the NIC.

When you want to troubleshoot a TCP/IP networking problem, first check the TCP/IP configuration of the computer that is experiencing the problem.

TO VIEW THE TCP/IP CONFIGURATION BY USING THE IPCONFIG.EXE

• ·      Click Start, click Run, type cmd, and then press ENTER.
• ·      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.
• ·      If you need more information and want to display a detailed configuration report, type ipconfig /all at the command prompt, and then press ENTER.
• ·      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.

TO DISPLAY CONNECTION INFORMATION BY USING THE NBTSTAT.EXE TOOL

NetBIOS over TCP/IP (NetBT) resolves NetBIOS names to IP addresses. TCP/IP provides many options for NetBIOS name resolution, including local cache lookup, WINS server query, broadcast, DNS server query, and LMHOSTS and HOSTS lookup.

Nbtstat.exe is a useful tool for troubleshooting NetBIOS name resolution problems. You can use the nbtstat.exe command to remove or correct preloaded entries. To use the nbtstat.exe command:

• To list the NetBIOS table of the local computer, type nbtstat -n at the command prompt, and then press ENTER. This command displays the names that were registered locally on the computer by programs such as the server and redirector.
• To list the contents of the NetBIOS name cache, type nbtstat -c at the command prompt, and then press ENTER. This command shows the NetBIOS name cache, which contains name-to-address mappings for other computers.
• To purge the name cache and reload it from the LMHOSTS file, type nbtstat -R at the command prompt, and then press ENTER.
• To perform a NetBIOS adapter status command against the computer that you specify by name, type nbtstat -a NetBIOS computer name at the command prompt, and then press ENTER. The adapter status command returns the local NetBIOS name table for that computer and the MAC address of the network adapter.

TO DISPLAY A LIST OF CLIENT AND SERVER CONNECTIONS, TYPE NBTSTAT -S AT

THE COMMAND PROMPT, AND THEN PRESS ENTER.

TESTING CONNECTIONS TO REMOTE SERVERS:

If you are unable to contact to a remote server, there are two common tools that you can use. Use the ping command to verify that a host computer can connect to the TCP/IP network and network resources. Use the tracert command to examine the route taken to a destination.

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 192.168.1.104) or ping host name (for example, ping www.microsoft.com), and then press ENTER.

3.     Check for a reply that may look like this:

Reply from 192.168.1.104: bytes=32 time=40ms TTL=61

If this message displays, the server is available on the network. 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.

TO TEST CONNECTIONS BY USING TRACERT.EXE

Tracert.exe is a route-tracing utility that you can use to determine the network path to a destination. To determine the path that a packet takes on the network and where that path may be ending:

• ·      Click Start, click Run, type cmd, and then press ENTER.
• ·      At the command prompt, type tracert IP address of the remote network host, and then press ENTER.
• ·      Examine the results to determine the length of time that the packet took to reach each network segment and the point at which the connection may stop working.

TO TEST CONNECTIONS BY USING THE NET VIEW COMMAND:

1.     Click Start, click Run, type cmd, and then press ENTER.

2.     At the command prompt, type net view \\computer name, and then press ENTER. A list of the file and print shares of a computer that is running Windows 2000 is generated by establishing a temporary NetBIOS connection. If there are no file or print shares available on the specified computer, you receive a "There are no entries in the list." message. If the command does not work, type net view \\IP address of the remote computer, and then press ENTER. If the command works, but a net view attempt to the computer name does not work, the computer name may be resolving to the wrong address. If the command does not work and generates a "System error has occurred" error message, verify that you typed the correct name of the remote computer, that the computer is operational (and is running the File and Printer Sharing for Microsoft Networks service), and that all of the gateways (routers) between the local computer and the remote host are operational by using the ping command.

Many organizations block the return of ICMP (ping) packets as a security measure. Because of this, if you are trying to contact a resource across the Internet, or critical internal systems, it may not be possible to obtain a response to a "ping" or "TRACERT" message.

I Can Ping a Resource by Its IP Address, but I Can Not "Ping" It by Name

If it is possible to contact a resource by using its IP address but a ping message to its host name does not work, the problem is likely caused by a name resolution failure, rather than network connectivity. Check to make sure that the computer is configured with the proper DNS or WINS entries, and that the DNS or WINS servers are available.

TROUBLESHOOTING FOR USB:

A.      If you install ActiveSync 3.6 on a new PC, you may not be able to sync and the system will ask you for USB drivers for your Pocket PC.  I suggest installing ActiveSync 3.5 first and then installing ActiveSync 3.6 to resolve this issue.

B.      If you are having problems with USB connections get the driver from the OEM if it is available.  Dell and Toshiba have a special USB driver that needs to be installed on the PC. The USB driver is included on the OEM cdrom provided or from their websites.

C.      If you are unable to connect with USB, try looking in the Device Manager for an unknown device.  If there is one when the Pocket PC is plugged in, then delete the device. Then reboot and try to connect again. An unknown device will be installed if you plugged your Pocket PC in before installing ActiveSync.

D.      If you are unable to connect with USB, try plugging the Pocket PC into any other USB ports. Some PCs now have both USB 1.1 and 2.0 ports.  Generally the Pocket PC works better with USB 1.1 ports.

E.       If you are unable to connect with USB, make sure that you have the latest rom bios installed on your PC. An example of this issue with recent bios include the Dell Dimension 8200 with bios version A07 dated 7-19-02 which would not work until it was upgrade to version A09.

F.       If you are having problems with USB connections, consider upgrading the Pocket PC's rom if it is available. I recommend only attempting the rom upgrade on a PC where the USB sync is stable for at least 15 minutes so you will need to find another PC to sync with.

G.      If you are having problems with staying connected via USB, make sure you install the latest BIOS updates for your motherboard.  Also, install the latest updates for USB for your motherboard.  See USB Man for updates. I also suggest plugging the Pocket PC directly into your PC instead of using a USB hub.  Some users have reported that they can synchronize if they unplug all other USB devices.

H.      Some users have reported that the use of an externally powered USB hub has allowed them to synchronize. (This has been reported to work for the Dell Axim).  Other users have reported some problems with using a USB hub.  I suggest trying to connect both ways.

I.        Other users have reported that their synchronization problems with the Toshiba Pocket PCs are diminished after they installed a newer USB 2.0 card from Belkin with 4 USB ports.

J.        If you are using the Dell Advanced Port Replicator (APR), plug the Pocket PC's USB cable directly to the Dell laptop instead.  You may see like "WCESMgr.exe - Application Error The instruction at 0x77235468 referenced memory at 0x00003000. The memory could not be read." if you attempt to sync using the APR.

K.      Apparently some USB 1.1 devices have too much jitter in their signals.  By using a USB 2.0 hub, the signal is retimed.

L.       If you have a Logitech Cordless TrackMan wheel model # T-RA18 plugged into your PC via USB you may find that the track ball freezes while you are synchronizing the Pocket PC.  At this time there is no work around or fix.

M.     Does your PC hang when you sync?  Do you have a USB Logitech Cordless Mouseman Wheel part # M-RL53 plugged in (drivers mw976enu and mw975wnu)?  If so you have a hardware conflict with the mouse and the Pocket PC.  I suggest considering another mouse instead.

N.      If your PC has USB 2.0 ports and is running Windows 2000 or Windows XP, and you turn on or off your Pocket PC or reboot your PC without disconnecting the Pocket PC it may not be detected.  You must install updated USB drivers.

O.      Some users have reported that they have been successful in synchronizing if they press the soft reset button while the cable is plugged into the Pocket PC and the PC.

TROUBLESHOOTING FOR WI-FI:

802.11 Ad-Hoc is the newer implementation and requires cards to be set both to the same channel and have the same ESSID in order to communicate.

Ad-Hoc is an older implementation and requires only that cards be set to the same channel and ignores the ESSID setting.

We recommend that you use the "802.11 Ad-Hoc" setting if your cards provide it, since it's slightly more secure.

If you are trying to set up a network of all wireless devices and do not have an "Access Point" to connect the wireless network into an Ethernet network, you will need to set your cards to operate in "AdHoc" mode.

WIRELESS LAN CARD SETTINGS FOR ACCESS POINT COMMUNICATION WHEN WE INSTALL OUR CLIENT CARDS, SET THE WIRELESS PROPERTIES AS FOLLOWS:

• ·        "AD HOC"- For direct card-to-card communication.
• ·        "INFRASTRUCTURE" - For communication through an Access Point.

If you are trying to set up a network that consists of mixed Ethernet and wireless clients, you'll need to use an Access Point (which bridges the two types of networks) and set your wireless card(s)' properties to match those of the Access Point.

Install your Access Point first and write down the values of the Properties below so that you have them when you set up your wireless clients. Then install your client card and set its wireless Properties as follows:

1) Channel
Set your card to the same channel as the Access Point.

You may be able to skip this step.  When set to Infrastructure mode, many wireless client card drivers automatically scan all channels until they find an Access Point with a matching ESSID.

2) Mode (or Network Type)
Set to Infrastructure.

3) SSID (or ESSID [Extended Service Set Identifier])
Set to the same as the alpha-numeric code as on the Access Point.

This is not the same as the BSSID (Basic Service Set Identifier), which is usually based on the MAC address of the card.

Set the ESSID to ANY to connect to any in-range Access Points.

4) Encryption (or WEP)
Set to disable. You can set this up after you get your connection working.  See this page for help.

If you've set all the above wireless Properties correctly and can't get a connection, check your TCP/IP properties.  If there is a DHCP server on your LAN (usually in your router), then set the wireless card's TCP/IP properties to obtain IP info from a DHCP server (or obtain info automatically).  Be sure that there is no gateway info entered and that DNS is disabled.  Sometimes doing a MANUAL RELEASE ALL / RENEW using either WINIPCFG OR IPCONFIG will get things working, even after a reboot.

If you're setting your IP info manually, you'll need to make sure you have your IP address set to a unique number in the same subnet as your Access Point.

Example: If your Access Point's IP address is 192.168.1.22, make sure your client card is set to a different number in the 192.168.X.X subnet.

OPEN YOUR WEB BROWSER

Some people assume all you have to do to check e-mail at a free Wi-Fi hotspot is turn on your computer, make sure the notebook has connected to the wireless network,

GET THE LATEST PASSWORD:

Many free Wi-Fi hotspot providers require you to enter a password to use the network. But for security reasons, a password that worked on Tuesday may have been changed by Sunday. To make sure you're up-to-date, ask someone in charge for the latest password. If you're at a hotel with free Wi-Fi, for instance, ask the front-desk clerk.

RESTART THE CONNECTION:

Sometimes, the software and hardware for a notebook's Wi-Fi adapter don't always get along with Windows XP. The result: Wi-Fi connections suddenly drop, without apparent reason.

One workaround is to stop and restart the wireless network service using the Microsoft Management Console in Windows. Begin by going to Start, Control Panel, "Performance, and Maintenance"; if you're in Category View, select Administrative Tools. Select Services. On the right side of the two-pane dialog box, scroll down to Wireless Zero Configurations and click to select it. Click "Stop the service" and, after that's accomplished, click "Start the service."

RESTART YOUR NOTEBOOK:

When I'm having difficulty making a wireless connection, restarting my notebook sometimes solves the problem. Why? It's a bit mysterious, but in general, some utilities and applications may conflict with one another or hog system resources. Restarting can flush out whatever ails your Wi-Fi connection, giving you a fresh start.

GET CLOSER:

If you're having problems making or keeping connections at a particular hotspot, your notebook could be too far from the wireless network access point. For instance, some hotel guests have reported that, even though they stayed in a hotel with in-room Wi-Fi, the wireless signal was too weak in their room to connect. If this happens to you, ask the front-desk clerk to move you to another room. Or if you're in a coffee shop or other public setting, ask someone in charge where the wireless signal is strongest.

EXTEND YOUR RANGE:

The antenna for built-in notebook Wi-Fi adapters is usually--no surprise here--built into the notebook, too. If you frequently have difficulty getting a strong signal, you might have better luck using a Wi-Fi adapter with a movable, external antenna. In some cases, an external antenna may be able to pick up weaker signals from nearby access points.

I've had good results with the Linksys WUSB12. The compact USB adapter for 802.11b networks features a small, folding antenna. The adapter can be connected directly to your notebook's USB port or, via a USB cable, positioned farther away so you can get a stronger signal.

For more tips on extending your Wi-Fi range, read the networking section in "Secret Tweaks."

ALSO UPGRADE TO WIN XP SP2:

For easier wireless network connectivity, diagnostics, and repair, consider installing the recent upgrade to the Windows XP operating system. Windows XP SP2 includes several wireless network enhancements, including a new Wireless Network Setup Wizard for easier setup and an enhanced Repair Wireless Network Connection tool. I've found that the latter can help make a wireless connection work when other efforts have failed.

To access the tool, right-click the Wireless Connection icon in the system tray on the bottom or right end of the Windows taskbar. From the context menu, select Repair to launch the tool.

Be aware, however, that many PC users continue to shy away from Windows XP SP2. The operating system upgrade includes enhanced networking and security features but can cause some applications installed on your PC to not work properly. (Windows XP SP2 came preinstalled on my current notebook, so I've not experienced any problems.) Read "Businesses Still Wary of XP SP2" for more about the ongoing problems.

USEFUL DOS NETWORKING COMMAND REFERENCE:

Some course material on the Teaching Network may still use the command line operating system called DOS (Disk Operating System). This requires the user to type specific commands at a prompt.

You may also need to use this system, for example, when changing your password, and you can enter DOS by choosing 'MS-DOS Prompt' from the Public menu on the taskbar.

Commands can be typed in response to the network DOS.

ipconfig – Windows IP Configuration
 

This has to the DOS command I use most today. ipconfig will tell you the IP settings for the current computer such as what your current IP is and what subnet/gateway you are on. It is great for troubleshooting. Here are the two most useful commands for ipconfig and usage:
 

ipconfig /release – This will release any IP information that the computer was given and make your IP address 0.0.0.0
 

ipconfig /renew – This will ask any DHCP servers (usually your modem/router) for a new IP address.

ping – Check a connection or computer
Ping is used to check the health of a connection. The ping command will tell you whether a network device is responding and how fast it is running. The ping tool can also be used to convert a web address into an IP (eg. www.google.com = 74.125.19.99). Usage:
ping www.google.com – Pings a webserver to see if it can be reached or is responding. I personally use this to see if the computer I am on can reach the internet.
ping 192.168.0.1 – Pings a local address, often a modem, router or another computer.

netstat – Displays current TCP/IP connections
netstat – Will display what connections are currently active on the system. Useful for spotting programs calling back to base such as spyware.

FILE MANAGEMENT:

type – Open texts files
Similar to Unix’s cat command, this command will display the contents of a text file in DOS as read-only. Usage:
type c:\sometextfile.txt

attrib – Make hidden files visible
Attrib can change the attributes of a file, such as whether its a system file or its hidden. This is especially useful to technicians because critical files such as the boot.ini is a hidden system file:
attrib -H c:\boot.ini – To unhide the boot.ini
attrib -S c:\boot.ini – To make remove its system file attribute

For more options with this command, type attrib /?

find – Advanced file search
The find command is a very powerful one with many options such as the ability to search for something, but exclude certain files. The following command will find all files with .pdf in their name on C:\
dir c:\ /s /b | find ".pdf"
For more information in this command and its usage, type find /?

move – Move files
Normal usage of the move command would be:
move file.txt c:\TextFiles\
However, you can also use it to move only certain files. For example, if I wanted to get all the PDF’s out of a folder and move them to another location, but leave all other file types alone, I would do:
move *.pdf c:\WorkPDFs\

tree – View the tree structure
Type tree to see the folder and file structure of the folder you are currently in. You can also use this command to make prints of the directory structure by sending the information to a text file with the following command tree > textfile.txt

System

systeminfo – Displays information about the system
systeinfo – Will display information about the system such as the name, version, uptime, specifications and patches installed.

tasklist / taskkill – Shows what programs are running on the computer and can kill them
tasklist – Will display all the processes running and their memory usage.
taskkill – Will kill a process. Usage would be: taskkill firefox.exe

sfc – Launches Windows’ system file checker utility
sfc /scannow – This command will start scanning your computer for any damaged or missing windows system files. Useful to run after a virus, adware or spyware attack has damaged core files. Have an XP CD handy for this one.

chkdsk – Can check a disk and attempt to recover data in bad sectors.
chkdsk /f /r – This will check a disk for errors and try and fixes information from bad sectors
chkdsk /x – Forces the volume to dismount first.

For further information/usage on any of these commands, you can bring up the help for each one of them by typing:
command /?

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 List of DOS commands = > http://en.wikipedia.org/wiki/List_of_DOS_commands

LAB EXAMPLE: TROUBLESHOOT TCP/IP CONNECTION WITH WIN XP:

STEPS AS FOLLOW -

• Network Diagnostics in Help and Support

Contains detailed information about the network configuration and the results of automated tests.

• Network Connections folder

Contains information and configuration for all network connections on the computer. To locate the Network Connections folder, click Start,

click Control Panel, and then click Network and Internet Connections.

• IPConfig command

Displays current TCP/IP network configuration values, updates, or releases, Dynamic Host Configuration Protocol (DHCP) allocated leases,

and display, register, or flush Domain Name System (DNS) names.

• Ping command

Sends ICMP Echo Request messages to verify that TCP/IP is configured correctly and that a TCP/IP host is available.

Advanced tools

• Hostname command

Displays the name of the host computer.

• Nbtstat command

Displays the status of current NetBIOS over TCP/IP connections, updates the NetBIOS name cache, and displays the registered names and

scope ID.

• PathPing command

Displays a path of a TCP/IP host and packet losses at each router along the way.

• Route command

Displays the IP routing table and adds or deletes IP routes.

• Tracert command

Displays the path of a TCP/IP host.

To view the correct command syntax to use with each of these tools, type -? at a command prompt after the name of the tool.

Windows XP Professional tools

Windows XP Professional contains the following additional tools:

• Event viewer

Records system errors and events.

• Computer Management

Changes network interface drivers and other components.

Troubleshooting

The procedure that you use to troubleshoot TCP/IP issues depends on the type of network connection that you are using and the connectivity

problem that you are experiencing.

Automated troubleshooting

For most issues that involve Internet connectivity, start by using the Network Diagnostics tool to identify the source of the issue. To use Network

DIAGNOSTICS, FOLLOW THESE STEPS:

1. Click Start, and then click Help and Support.

2. Click the link to Use Tools to view your computer information and diagnose problems, and then click Network Diagnostics in the

list on the left.

3. When you click Scan your system, Network Diagnostics gathers configuration information and performs automated troubleshooting of the

network connection.

4. When the process is completed, look for any items that are marked "FAILED" in red, expand those categories, and then view the additional

details about what the testing showed.

You can either use that information to resolve the issue or you can provide the information to a network support professional for help. If you

compare the tests that failed with the documentation in the Manual Troubleshooting section later in this article, you may be able to determine the

source of the issue. To interpret the results for TCP/IP, expand the Network Adapters section of the results, and then expand the network adapter

that failed the testing.

You can also start the Network Diagnostics interface directly by using the following command:

netsh diag gui

Manual troubleshooting

To manually troubleshoot your TCP/IP connectivity, use the following methods in the order that they appear:

Method 1: Use the IPConfig tool to verify the configuration

To use the IPConfig tool to verify the TCP/IP configuration on the computer that is experiencing the problem, click Start, click Run, and then type

cmd. You can now use the ipconfig command to determine the host computer configuration information, including the IP address, the subnet

mask, and the default gateway.

The /all parameter for IPConfig generates a detailed configuration report for all interfaces, including any remote access adapters. You can redirect

IPConfig output to a file to paste the output into other documents. To do this, type:

ipconfig > \folder_name\file_name

The output receives the specified file name and is stored in the specified folder.

You can review the IPConfig output to identify issues that exist in the computer network configuration. For example, if a computer is manually

configured with an IP address that duplicates an existing IP address that is already detected, the subnet mask appears as 0.0.0.0.

If your local IP address is returned as 169.254.y.z with a subnet mask of 255.255.0.0, the IP address was assigned by the Automatic Private IP

Addressing (APIPA) feature of Windows XP Professional. This assignment means that TCP/IP is configured for automatic configuration, that no DHCP

server was found, and that no alternative configuration is specified. This configuration has no default gateway for the interface.

If your local IP address is returned as 0.0.0.0, the DHCP Media Sensing feature override turned on because the network adapter detected its lack of

connection to a network, or TCP/IP detected an IP address that duplicates a manually configured IP address.

If you do not identify any issues in the TCP/IP configuration, go to Method 2.

Method 2: Use the Ping tool to test your connectivity

If you do not identify any issues in the TCP/IP configuration, determine whether the computer can connect to other host computers on the TCP/IP

network. To do this, use the Ping tool.

The Ping tool helps you verify IP-level connectivity. The ping command sends an ICMP Echo Request message to a destination host. Use Ping

whenever you want to verify that a host computer can send IP packets to a destination host. You can also use Ping to isolate network hardware

problems and incompatible configurations.

Note If you ran the ipconfig /all command, and the IP configuration appeared, you do not have to ping the loopback address and your own IP

address. IPConfig has already performed these tasks to display the configuration. When you troubleshoot, verify that a route exists between the

local computer and a network host. To do this, use the following command:

ping IP address

NoteIP address is the IP address of the network host that you want to connect to.

To use the ping command, follow these steps:

1. Ping the loopback address to verify that TCP/IP is installed and correctly configured on the local computer. To do this, type the following

command:

ping 127.0.0.1

If the loopback test fails, the IP stack is not responding. This problem may occur if any one or more of the following conditions is true:

• The TCP drivers are corrupted.

• The network adapter is not working.

• Another service is interfering with IP.

2. Ping the IP address of the local computer to verify that the computer was correctly added to the network. If the routing table is correct, this

procedure just forwards the packet to the loopback address of 127.0.0.1. To do this, type the following command:

ping IP address of local host

If the loopback test succeeds but you cannot ping the local IP address, there may be an issue with the routing table or with the network

adapter driver.

3. Ping the IP address of the default gateway to verify that the default gateway is working and that you can communicate with a local host on

the local network. To do this, type the following command:

ping IP address of default gateway

If the ping fails, you may have an issue with the network adapter, the router or gateway device, the cabling, or other connectivity hardware.

4. Ping the IP address of a remote host to verify that you can communicate through a router. To do this, type the following command:

ping IP address of remote host

If the ping fails, the remote host may not be responding, or there may be a problem with the network hardware between computers. To rule

out an unresponsive remote host, use Ping again to a different remote host.

5. Ping the host name of a remote host to verify that you can resolve a remote host name. To do this, type the following command:

ping Host name of remote host

Ping uses name resolution to resolve a computer name into an IP address. Therefore, if you successfully ping an IP address but you cannot

ping a computer name, there is a problem with host name resolution, not with network connectivity. Verify that DNS server addresses are

configured for the computer, either manually in the properties of TCP/IP, or by automatic assignment. If DNS server addresses are listed

when you type the ipconfig /all command, try to ping the server addresses to make sure that they are accessible.

IF YOU CANNOT USE PING SUCCESSFULLY AT ANY POINT, VERIFY THE FOLLOWING CONFIGURATIONS:

• Make sure that the local computer's IP address is valid and that it is correct on the General tab of the Internet Protocol (TCP/IP)

Properties dialog box or when it is used with the Ipconfig tool.

• Make sure that a default gateway is configured and that the link between the host and the default gateway is working. For troubleshooting

purposes, make sure that only one default gateway is configured. Although you can configure more than one default gateway, gateways after

the first gateway are used only if the IP stack determines that the original gateway is not working. The purpose of troubleshooting is to

determine the status of the first configured gateway. Therefore, you can delete all the other gateways to simplify your task.

• Make sure that Internet Protocol security (IPSec) is not turned on. Depending on the IPSec policy, Ping packets may be blocked or may

require security. For more information about IPSec, go to Method 7: Verify Internet Protocol security (IPSec).

Important If the remote computer that you are pinging is across a high-delay link such as a satellite link, response may take longer. You can use

the -w (wait) parameter to specify a longer timeout period than the default timeout of four seconds.

Method 3: Use the PathPing tool to verify a route

The PathPing tool detects packet loss over multiple-hop paths. Run a PathPing analysis to a remote host to verify that the routers on the way to the

destination are operating correctly. To do this, type the following command:

pathping IP address of remote host

Method 4: Use the Arp tool to clear the ARP cache

If you can ping both the loopback address (127.0.0.1) and your IP address but you cannot ping any other IP addresses, use the Arp tool to clear

out the Address Resolution Protocol (ARP) cache. To view the cache entries, type any one of the following commands:

arp -a

arp -g

To delete the entries, type the following command:

arp -d IP address

To flush the ARP cache, type the following command:

netsh interface ip delete arpcache

Method 5: Verify the default gateway

The gateway address must be on the same network as the local host. Otherwise, messages from the host computer cannot be forwarded outside

the local network. If the gateway address is on the same network as the local host, make sure that the default gateway address is correct. Make

sure that the default gateway is a router, not just a host. And make sure that the router is enabled to forward IP datagrams.

Method 6: Use the Tracert tool or the Route tool to verify communications

If the default gateway responds correctly, ping a remote host to make sure that network-to-network communications are working correctly. If

communications are not working correctly, use the Tracert tool to trace the path of the destination. For IP routers that are Microsoft Windows

2000-based or Microsoft Windows NT 4.0-based computers, use the Route tool or the Routing and Remote Access snap-in to view the IP routing

table. For other IP routers, use the vendor-designated appropriate tool or facility to examine the IP routing table.

Most frequently, you receive the following four error messages when you use Ping during troubleshooting:

TTL EXPIRED IN TRANSIT:

This error message means that the number of required hops exceeds the Time to Live (TTL). To increase TTL, by use the ping -i command. A

routing loop may exist. Use the Tracert command to determine whether misconfigured routers have caused a routing loop.

DESTINATION HOST UNREACHABLE:

This error message means that no local or remote route exists for a destination host at the sending host or at a router. Troubleshoot the local host

or the router's routing table.

REQUEST TIMED OUT:

This error message means that the Echo Reply messages were not received in the designated timeout period. By default, the designated timeout

period is four seconds. Use the ping -w command to increase the timeout.

PING REQUEST COULD NOT FIND HOST:

This error message means that the destination host name cannot be resolved. Verify the name and the availability of DNS or WINS servers.

Method 7: Verify Internet Protocol security (Ipsec)

IPSec can improve security on a network, but changing network configurations or troubleshooting problems more difficult. Sometimes, IPSec

policies require secured communication on a Windows XP Professional-based computer. These requirements can make it difficult to connect to a

remote host. If IPSec is implemented locally, you can turn off the IPSEC Services service in the Services snap-in.

If the difficulties end when you stop the IPSec services, IPSec policies are either blocking the traffic or requiring security for the traffic. Ask the

security administrator to modify the IPSec policy.

Method 8: Verify packet filtering

Because of mistakes in packet filtering, address resolution or connectivity may not work. To determine whether packet filtering is the source of a

NETWORK PROBLEM, TURN OFF TCP/IP PACKET FILTERING. TO DO THIS, FOLLOW THESE STEPS:

1. Click Start, click Control Panel, click Network and Internet Connections, and then click Network Connections.

2. Right-click the local area connection that you want to modify, and then click Properties.

3. On the General tab, in the This connection uses the following items list, click Internet Protocol (TCP/IP), and then click

Properties.

4. Click Advanced, and then click the Options tab.

5. In the Optional Settings dialog box, click TCP/IP Filtering, and then click the Properties tab.

6. Click to clear the Enable TCP/IP Filtering (All adapters) check box, and then click OK.

To ping an address, use its DNS name, its NetBIOS computer name, or its IP address. If the ping succeeds, the packet filtering options may be misconfigured or too restrictive. For example, the filtering can allow the computer to act as a Web server, but, to do this, the filtering may turn off

tools such as remote administration. To restore a wider range of permissible filtering options, change the permitted values for the TCP port, the UDP

port, and the IP protocol.

Method 9: Verify the connection to a specific server

To determine the cause of connectivity problems when you are trying to connect to a specific server through NetBIOS-based connections, use the

nbtstat -n command on the server to determine what name the server registered on the network.

The nbtstat -n output command lists several names that the computer has registered. The list will include a name that looks similar to the

computer's name that is configured on the Computer Name tab under System in Control Panel. If not, try one of the other unique names that the

nbtstat command displays.

The Nbtstat tool can also display the cached entries for remote computers from #PRE entries in the Lmhosts file or from recently resolved names. If

the name that the remote computers are using for the server is the same, and the other computers are on a remote subnet, make sure that the

other computers have the computer's name-to-address mapping in their Lmhosts files or WINS servers.

Method 10: Verify remote connections

To determine why a TCP/IP connection to a remote computer stops responding, use the netstat -a command to show the status of all activity for

TCP and UDP ports on the local computer.

Typically, a good TCP connection shows 0 bytes in the Sent and Received queues. If data is blocked in either queue or the state of the queues is

irregular, the connection may be faulty. If data is not blocked, and the state of the queues is typical, you may be experiencing network or program

delay.

Method 11: Use the Route tool to examine the routing table

For two hosts to exchange IP datagrams, both hosts must have a route to each other, or they must use default gateways that have a route. To view

the routing table on a Windows XP-based host, type the following command:

route print

Method 12: Use the Tracert tool to examine paths

Tracert sends ICMP Echo Request messages that have incrementally higher values in the IP header TTL field to determine the path from one host to

another through a network. Then Tracert analyzes the ICMP messages that are returned. With Tracert, you can track the path from router to router

for up to 30 hops. If a router has failed, or the packet is routed into a loop, Tracert reveals the problem. After you locate the problem router, you

can contact the router administrator if the router is offsite, or you can restore the router to fully functional status if the router is under your control.

Method 13: Troubleshoot gateways

If you receive the following error message during configuration, determine whether the default gateway is located on the same logical network as

the computer's network adapter:

Your default gateway does not belong to one of the configured interfaces

Compare the network ID part of the default gateway IP address with the network IDs of the computer's network adapters. Specifically, verify that

the bitwise logical AND of the IP address and the subnet mask equals the bitwise logical AND of the default gateway and the subnet mask.

For example, a computer that has a single network adapter that is configured with an IP address of 172.16.27.139 and a subnet mask of

255.255.0.0 must use a default gateway of the form 172.16.y.z. The network ID for this IP interface is 172.16.0.0.

ADDITIONAL RESOURCES

The following resources contain additional information about how to troubleshoot Microsoft TCP/IP:

See the "Configuring TCP/IP" topic in the documentation for the Microsoft Windows XP Professional Resource Kit.

See "Introduction to TCP/IP" in the TCP/IP Core Networking Guide of the Microsoft Windows 2000 Server Resource Kit for general information about

the TCP/IP protocol suite.

See "Unicast Routing Overview" in the Internetworking Guide of the Microsoft Windows 2000 Server Resource Kit for more information about

routing principles.

See "TCP/IP Troubleshooting" in the TCP/IP Core Networking Guide of the Microsoft Windows 2000 Server Resource Kit for more information about

IP packet filtering.

This Article Written Author By: Premakumar Thevathasan. CCNA, CCNP, CCIP, MCSA, MCSE, MCSA - MSG, CIW Security Analyst, CompTIA Certified A+.