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Troubleshooting Your LAN

Troubleshooting the LAN is part of the job of a technical support provider/network administrator. In your role as a troubleshooter, you should: Encourage the users on your network to come to you when they experience network difficulties. Learn simple troubleshooting techniques to try before you call the NOC. Learn how to gather information that will be helpful and useful to the NOC when you do need to submit a Problem Report. The rest of this page discusses some common problems and solutions to them. You should run through these solutions before calling the NOC for help. If you don't have any success fixing your network problem, you will need to submit a Problem Report to the Network Operations Center.

Some common problems are listed below, click on the problem to view possible solutions:

• Troubleshooting Guide for Macintosh Computers on Ethernet Networks
• Devices are displayed in the Chooser, but you have no IP access.
• No devices are displayed in the Chooser and there is no IP access.
• No devices are displayed in the Chooser and you have IP access.
• Single user has devices but cannot connect to any IP services (CornellC, POPMail, CUinfo,
  etc.).
• Single user has no devices and no IP connectivity.
• Multiple users have devices but no connectivity to a specific IP service (e.g. COLTS).
• Multiple users have no devices and no IP connectivity, but local resources such as printers and file servers are available.
• Multiple users have no devices and no IP connectivity, and local resources such as printers and file servers are not available.
• Printer or file server not accessible.

• Troubleshooting Guide for PCs on Ethernet Networks
  • Cannot find Novell server.
  • Cannot connect to host or no ARP response from router.
  • Error message when connecting to TCP/IP application.
  • Error connecting to a host computer.
  • Printer or file server not accessible.

• Other Problems

 

Troubleshooting Guide for Macintosh Computers on Ethernet Networks

Problem	Likely Cause
Devices are displayed in the Chooser, but you have no IP access. You may see an error message, such as "Can't connect to host."	Incorrect network settings or bad cable.

Solutions:

1. The workstation's MacTCP or Open Transport software may not be configured correctly. Check the MacTCP or TCP/IP configuration file to be sure a unique IP address has been assigned to the workstation.

2. Check if the problem is with one user or everyone on the network. If the problem exists only with one user, it's likely that the IP address of that workstation is incorrect. If the entire network can't get to a particular service, it is likely that the service is down.

3. If the above steps do not solve the problem, try the following:

   • Select the Network icon on the Control Panel and look at the selected icons. If LocalTalk/Built-in is selected, select EtherTalk instead.

   • If the problem persists after checking the network settings, do a quick test to see if the cable is at fault. Borrow a cable that you know is good from another node. Plug it in and see if the node works. If it does, you now know you need to permanently replace the cable.

 

Problem	Likely Cause
No devices are displayed in the Chooser and there is no IP access.	Incorrect network settings or bad cable.

Solutions:

1. Do a quick test to see if the cable is at fault. Borrow a cable that you know is good from another node. Plug it in and see if the node works. If it does, you now know you need to permanently replace the cable.
   
2. Select the Network icon on the Control Panel and look at the selected icons. If LocalTalk/Built-In is selected, select EtherTalk instead.
   
3. Go to the Control Panel and select the MacTCP or TCP/IP icon. Check the displayed settings. Ethernet, not EtherTalk, must be selected. Change the setting if necessary.
   
4. Go to the Chooser and check the displayed settings. AppleTalk must be turned on in the Chooser.

 

Problem	Likely Cause
No devices displayed in the Chooser, but you have IP access (i.e. Bear Access clients).	Incorrect network settings or bad cable.

Solutions:

1. Select the Network icon on the Control Panel and look at the selected icons. If LocalTalk/Built-in is selected, select EtherTalk instead.
   
2. If the problem persists after checking the network settings, do a quick test to see if the cable is at fault. Borrow a cable that you know is good from another node. Plug it in and see if the node works. If it doesn't, you know you need to permanently replace the cable.

 

Problem	Likely Cause(s)
Single user has devices but cannot connect to any IP services (CornellC, POPMail, CUinfo, etc.).	MacTCP or Open Transport configured incorrectly (Remember: each node/IP number must by unique).
	Communications software (Bear Access or MacTCP and Comet) are corrupt or version is incorrect.

Solutions:

• Check MacTCP or TCP/IP settings and correct.
• Reinstall the latest version of the software.

 

Problem	Likely Cause(s)
Single user has no devices and no IP connectivity.	Bad Ethernet card.
	Cable not connected properly.
	Cable is bad.

Solutions:

• Swap out Ethernet card for one you know is working (keep a spare on hand).
• Make sure one end of cable is firmly plugged into Ethernet card and the other end is firmly connected to the receptacle of phone jack.
• Swap out cable for one you know is working (keep spares on hand).

 

Problem	Likely Cause(s)
Multiple users have devices, but no connectivity to specific IP service (e.g. COLTS).	The server or host machine for that service is down.

Solutions:
Check the Network Status page, the net-announce-1 discussion list, or AUDIX to see if the NOC is aware of the problem and has posted it. If not, call the NOC at 5-9900 to report the problem. Tell your users to work on something else in the meantime.

 

Problem	Likely Cause(s)
Multiple users have no devices, no IP connectivity, but local resources such as printers and file servers are available.	Your router is down.

Solution:
Call the NOC at 5-9900 with the IP address of your router.

 

Problem	Likely Cause(s)
Multiple users have no devices, no IP connectivity, and local resources such as printers and file servers are not available.	The network switch or concentrator has failed.

Solution:
Call the NOC at 5-9900.

 

Problem	Likely Cause(s)
Printer or file server not accessible.	Host IP address might be incorrect.
	Host computer might be down.

Solution:

1. Restart the printer or file server.
2. Check to see if the printer or file server is plugged into the right port on the jack (often side 2).
3. Check to see if the network cable is connected to the printer or file server.

 

Troubleshooting Guide for PCs on Ethernet Networks

Problem	Likely Cause(s)
Cannot find Novell file server.	Incorrect network settings or problem with file server.

Solution:

Windows 98/Me/NT 4

Check the Network Neighborhood to see if the server shows up there.

1. If it does not, check in Entire Network to see if any servers appear.
   
2. If other servers appear and yours does not, then there is a problem with the server not just for one computer but for everyone accessing this server.
   
3. If no other servers appear, then you may have a configuration problem in Windows 98/Me/NT 4 or a communication problem with the network.
   
   • Launch Bear Access to verify that the network card is working.
     
   • If it is working, go into the control panel and double-click the Network icon. In NT 4, click on the Services or Protocols tab to see the Client for Netware Networks.
     
   • Double-click the Client for Netware Networks.
     
   • Look at the settings to see if they are correct.
     
   • Close the client and open IPX/SPX.
     
   • Look in bindings to see if it is bound to the Client for Netware Networks.

 

Problem	Likely Cause(s)
Cannot connect to host or no ARP response from router.	Cable is bad.

Solution:
Do a quick test to see if the cable is at fault. Borrow a cable that you know is good from another node. Plug it in and see if the node works. If it does, you know you need to permanently replace the cable.

 

Problem	Likely Cause(s)
Error message when connecting to a TCP/IP application.	Cable is bad.

Solution:
Each application should have the IP address you assigned to the workstation stored in a configuration file. Find the configuration file for that application and make sure the IP address is correct. Also check the router address, which is the same as the IP address except for the last number.

Example: IP address: 128.253.208.23; possible gateway addresses:

128.253.208.1.
128.253.208.65
128.253.208.129
128.253.208.193


For more about router addresses see Overview of IP addresses, subnetting and sub-subnetting. If the configuration file defines a network mask, this number may be 255.255.255.0 or 255.255.255.128 or 255.255.255.192.

 



Problem	Likely Cause(s)
Error connecting to a host computer.	Host IP address might be incorrect.
	Host computer might be down.

Solution:
If unable to connect to more than one host, check the local workstation IP and router addresses.

 



Problem	Likely Cause(s)
Printer or file server not accessible.	Host IP address might be incorrect.
	Host computer might be down.

Solution:

1. Restart the printer or file server.
2. Check to see if the printer or file server is plugged into the right port on the jack (often side 2).
3. Check to see if the network cable is connected to the printer or file server.

 

Other Problems

Conflicts between networking software, memory management software, Ethernet card setups, etc. can occur. This is site-specific information that might affect network performance. Network problems occurring after changes in workstation configurations are likely to be caused by those changes, especially if network services were available and working correctly before the workstation configuration change.

 

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Last updated: February 11, 2002
Reformatted: June 04, 2007