Windows 7 / Networking

How to Troubleshoot Application Connectivity Problems

Sometimes, you might be able to access the network with some applications but not others. For example, you might be able to download your e-mail but not access Web servers. Or, you might be able to view pages on a remote Web server but not connect to the computer with Remote Desktop.

Several issues might cause these symptoms (in rough order of likelihood):

  • The remote service is not running. For example, 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 your 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 non-default port number. For example, Web servers typically use TCP port 80, but some administrators might configure TCP port 81 or a different port.

To troubleshoot an application connectivity problem, follow these steps:

  1. Before you begin troubleshooting application connectivity, first verify that you do not have a name resolution problem. To do this, open a command prompt and run the command Nslookup servername. If Nslookup does not display an answer similar to the following example, you have a name resolution problem. See the section titled "How to Troubleshoot Name Resolution Problems" later in this tutorial.
    Non-authoritative answer:
  2. Identify the port number used by the application.

Table next section lists port numbers for common applications.

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In this tutorial:

  1. Troubleshooting Network Issues
  2. Tools for Troubleshooting
  3. Table-1 Network Troubleshooting Tools
  4. Arp
  5. How to Identify a Problem with the ARP Cacher
  6. How to Clear the ARP Cache
  7. Event Viewer
  8. IPConfig
  9. Nblookup
  10. Nbtstat
  11. Net
  12. How to View Shared Folders on the Local Computer
  13. How to View Shared Folders on Another Computer
  14. Netstat
  15. Network Monitor
  16. Nslookup
  17. Verifying that the Default DNS Server Resolves Correctly
  18. Verifying that a Specific DNS Server Resolves Correctly
  19. Verifying Specific Types of Addresses
  20. Using TCP for DNS Lookups
  21. PathPing
  22. PathPing Output
  23. Routing Loops
  24. Performance Problems
  25. Possible Connectivity Issues
  26. No Connectivity Issues
  27. Performance Monitor
  28. Data Collector Sets
  29. Windows Resource Monitor
  30. Ping
  31. PortQry
  32. Identifying the TCP Port for a Service
  33. Windows 7 Testing Service Connectivity
  34. Determining Available Remote Management Protocols
  35. Why PortQry Is Great
  36. Route
  37. Task Manager
  38. TCPView
  39. Telnet Client
  40. Testing Service Connectivity
  41. Test TCP
  42. Windows Network Diagnostics
  43. The Process of Troubleshooting Network Problems
  44. How to Troubleshoot Network Connectivity Problems
  45. How to Troubleshoot Application Connectivity Problems
  46. Default Port Assignments for Common Services and Tasks
  47. How to Troubleshoot Name Resolution Problems
  48. How to Verify Connectivity to a DNS Server
  49. How to Use the Hosts File
  50. How to Troubleshoot Performance Problems and Intermittent Connectivity Issues
  51. How to Troubleshoot Joining or Logging on to a Domain
  52. How to Verify Requirements for Joining a Domain
  53. How to Troubleshoot Network Discovery
  54. How to Troubleshoot File and Printer Sharing
  55. How to Troubleshoot File and Printer Sharing from the Client
  56. How to Troubleshoot File and Printer Sharing from the Server
  57. How to Troubleshoot Wireless Networks
  58. Network Diagnostics
  59. How to Troubleshoot Firewall Problems