Logo
programming4us
programming4us
programming4us
programming4us
Home
programming4us
XP
programming4us
Windows Vista
programming4us
Windows 7
programming4us
Windows Azure
programming4us
Windows Server
programming4us
Windows Phone
 
programming4us
Windows 7

The Process of Troubleshooting Network Problems (part 2) - How to Troubleshoot Application Connectivity Problems

- Free product key for windows 10
- Free Product Key for Microsoft office 365
- Malwarebytes Premium 3.7.1 Serial Keys (LifeTime) 2019
11/4/2012 6:16:32 PM

2. 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. 

    C:\>nslookup contoso.com
    
    
     Non-authoritative answer:
     Name:    contoso.com
     Addresses:  10.46.232.182, 10.46.130.117

  2. Identify the port number used by the application. Table 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. Alternatively, you can use a protocol analyzer, such as Network Monitor, to examine network traffic to determine the port numbers used.

Table 1. Default Port Assignments for Common Services and Tasks
SERVICE NAME OR TASKUDPTCP
Web servers, HTTP, and Internet Information Services (IIS) 80
HTTP- Secure Sockets Layer (SSL) 443
DNS client-to-server lookup (varies)5353
DHCP client 67
File and printer sharing137139, 445
FTP-control 21
FTP-data 20
Internet Relay Chat (IRC) 6667
Microsoft Office Outlook (see POP3, IMAP, and SMTP for ports)  
Internet Mail Access Protocol (IMAP) 143
IMAP (SSL) 993
LDAP 389
LDAP (SSL) 636
Message Transfer Agent (MTA) – X.400 over TCP/IP 102
POP3 110
POP3 (SSL) 995
RPC endpoint mapper 135
SMTP 25
Network News Transfer Protocol (NNTP) 119
NNTP (SSL) 563
POP3 110
POP3 (SSL) 995
SNMP161 
SNMP Trap162 
SQL Server 1433
Telnet 23
Terminal Server and Remote Desktop 3389
Point-to-Point Tunneling Protocol (PPTP)  1723
Joining an AD DS domain   

After identifying the port number, the first step in troubleshooting the application connectivity problem is to determine whether communications are successful using that port. If it is a TCP port, you can use PortQry, Test TCP, or Telnet. Of those three tools, Telnet is the least flexible, but it is the only tool included with Windows (but note that it is not installed by default). 

To test a TCP port with Telnet, 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 have successfully established a connection. Close the command prompt to cancel Telnet. This indicates that you can connect to the server; therefore, the server application is listening for incoming connections and no firewall is blocking your traffic. Instead of troubleshooting the problem as a connectivity issue, you should consider application-level issues, including:

  • Authentication issues View the server's Security Event Log or the application's log to determine whether it is rejecting your client connections because of invalid credentials.

  • Failed service Restart the server. Test whether other client computers can connect to the server.

  • Invalid client software Verify that the client software running on your computer is the correct version and is configured properly.

If Telnet displays "Could not open connection to the host," this indicates an application connectivity issue, such as a misconfigured firewall. Follow these steps to continue troubleshooting the problem:

  1. If possible, verify that the server is online. If the server is online, attempt to connect 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.

  2. Attempt to connect from different client computers on the same and different subnets. If you can connect from a client computer on the same subnet, you might have an application configuration problem on the client computer. 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 might be filtering traffic from your client network.

  3. If possible, connect a client computer to the same subnet as the server. If you can connect from the same subnet but not from different subnets, a router-based firewall is blocking traffic. If you cannot connect from the same subnet, the server has a firewall that is blocking traffic. Alternatively, the server application might not be running or might be configured to use a different port.

  4. Log on to the server and use Telnet to attempt to connect to the server application port. If you can connect to the server from the server but not from other computers, the server definitely has firewall software configured. Add an exception for the application to the firewall software. If you cannot connect to the server application from the server, the application is not listening for connections or is configured to listen for incoming connections on a different port. Refer to the application documentation for information on how to start and configure the application. If the server is running Windows, you can use Netstat to identify on which ports the server is listening for incoming connections.

Other -----------------
- Microsoft Excel 2010 : Analyzing Data by Using Descriptive Statistics
- Microsoft Excel 2010 : Finding Optimal Solutions by Using Solver
- Microsoft Excel 2010 : Varying Your Data to Get a Desired Result by Using Goal Seek
- Microsoft Word 2010 : Working with Outlines - Working with Master Documents
- Microsoft Word 2010 : Working with Outlines - Creating a Standard Outline
- Using Microsoft OneNote 2010 with Other Programs : OneNote Integration with Internet Explorer
- Using Microsoft OneNote 2010 with Other Programs : A Quick Note About Interface Differences, OneNote Integration with Windows
- Conquering Malicious Software : Conquering Spyware with Windows Defender
- Parental Controls and Family Safety : Using Parental Controls from Windows Live
- Parental Controls and Family Safety : Using the Built-In Parental Controls
 
 
Top 10
- Microsoft Visio 2013 : Adding Structure to Your Diagrams - Finding containers and lists in Visio (part 2) - Wireframes,Legends
- Microsoft Visio 2013 : Adding Structure to Your Diagrams - Finding containers and lists in Visio (part 1) - Swimlanes
- Microsoft Visio 2013 : Adding Structure to Your Diagrams - Formatting and sizing lists
- Microsoft Visio 2013 : Adding Structure to Your Diagrams - Adding shapes to lists
- Microsoft Visio 2013 : Adding Structure to Your Diagrams - Sizing containers
- Microsoft Access 2010 : Control Properties and Why to Use Them (part 3) - The Other Properties of a Control
- Microsoft Access 2010 : Control Properties and Why to Use Them (part 2) - The Data Properties of a Control
- Microsoft Access 2010 : Control Properties and Why to Use Them (part 1) - The Format Properties of a Control
- Microsoft Access 2010 : Form Properties and Why Should You Use Them - Working with the Properties Window
- Microsoft Visio 2013 : Using the Organization Chart Wizard with new data
 
programming4us
Windows Vista
programming4us
Windows 7
programming4us
Windows Azure
programming4us
Windows Server