Section 6.3. Get Information About a Network Connection


6.3. Get Information About a Network Connection

Some applications need to adjust how they work based on whether a network connection is present. For example, imagine a sales reporting tool that runs on the laptop of a traveling sales manager. When the laptop is plugged into the network, the application needs to run in a connected mode in order to retrieve the information it needs, such as a list of products, directly from a database or web service. When the laptop is disconnected from the network, the application needs to gracefully degrade to a disconnected mode that disables certain features or falls back on slightly older data that's stored in a local file. To make the decision about which mode to use, an application needs a quick way to determine the network status of the current computer. Thanks to the new My.Computer.Network object, this task is easy.


Note: Need to find out if your computer's currently online? With the My class, this test is just a simple property away.

6.3.1. How do I do that?

The My.Computer.Network object provides a single IsAvailable property that allows you to determine if the current computer has a network connection. The IsAvailable property returns TRue as long as at least one of the configured network interfaces is connected, and it serves as a quick-and-dirty test to see if the computer is online. To try it out, enter the following code in a console application:

If My.Computer.Network.IsAvailable Then     Console.WriteLine("You have a network interface.") End If

If you want more information, you need to turn to the System.Net and System.Net.NetworkInformation namespaces, which provide much more fine-grained detail. For example, to retrieve and display the IP address for the current computer, you can use the System.Net.Dns class by entering this code:

' Retrieve the computer name. Dim HostName As String = System.Net.Dns.GetHostName( ) Console.WriteLine("Host name: " & HostName)      ' Get the IP address for this computer. ' Note that this code actually retrieves the first ' IP address in the list, because it assumes the ' computer only has one assigned IP address ' (which is the norm). Console.WriteLine("IP: " & _   System.Net.Dns.GetHostByName(HostName).AddressList(0).ToString( ))

Here's the output you might see:

Host name: FARIAMAT IP: 192.168.0.197

In addition, you can now retrieve even more detailed information about your network connection that wasn't available in previous versions of .NET. To do so, you need to use the new System.Net.NetworkInformation.IPGlobalProperties class, which represents network activity on a standard IP network.

The IPGlobalProperties class provides several methods that allow you to retrieve different objects, each of which provides statistics for a specific type of network activity. For example, if you're interested in all the traffic that flows over your network connection using TCP, you can call IPGlobalProperties.GetTcpIPv4Statistics(). For most people, this is the most useful measurement of the network. On the other hand, if you're using a next-generation IPv6 network, you need to use IPGlobalProperties.GetTcpIPv6Statistics(). Other methods exist for monitoring traffic that uses the UPD or ICMP protocols. Obviously, you'll need to know a little bit about networking to get the best out of these methods.


Tip: IP (Internet Protocol) is the core building block of most networks and the Internet. It uniquely identifies computers with a four-part IP address, and allows you to send a basic packet from one machine to another (without any frills like error correction, flow control, or connection management). Many other networking protocols, such as TCP (Transmission Connection Protocol) are built on top of the IP infrastructure, and still other protocols are built on top of TCP (e.g., HTTP, the language of the Web). For more information about networking, refer to a solid introduction such as Internet Core Protocols (O'Reilly).

The following code retrieves detailed statistics about the network traffic. It assumes that you've imported the System.Net.NetworkInformation namespace:

Dim Properties As IPGlobalProperties = IPGlobalProperties.GetIPGlobalProperties( ) Dim TcpStat As TcpStatistics TcpStat = Properties.GetTcpIPv4Statistics( )      Console.WriteLine("TCP/IPv4 Statistics:") Console.WriteLine("Minimum Transmission Timeout... : " & _   TcpStat.MinimumTransmissionTimeOut) Console.WriteLine("Maximum Transmission Timeout... : " & _   TcpStat.MaximumTransmissionTimeOut)      Console.WriteLine("Connection Data:") Console.WriteLine("  Current  .................... : " & _   TcpStat.CurrentConnections) Console.WriteLine("  Cumulative .................. : " & _   TcpStat.CumulativeConnections) Console.WriteLine("  Initiated ................... : " & _   TcpStat.ConnectionsInitiated) Console.WriteLine("  Accepted .................... : " & _   TcpStat.ConnectionsAccepted) Console.WriteLine("  Failed Attempts ............. : " & _   TcpStat.FailedConnectionAttempts) Console.WriteLine("  Reset ....................... : " & _   TcpStat.ResetConnections)      Console.WriteLine( ) Console.WriteLine("Segment Data:") Console.WriteLine("  Received  ................... : " & _   TcpStat.SegmentsReceived) Console.WriteLine("  Sent ........................ : " & _   TcpStat.SegmentsSent) Console.WriteLine("  Retransmitted ............... : " & _   TcpStat.SegmentsResent)

Here's the output you might see:

TCP/IPv4 Statistics: Minimum Transmission Timeout... : 300 Maximum Transmission Timeout... : 120000 Connection Data:   Current  .................... : 6   Cumulative .................. : 29   Initiated ................... : 10822


Note: Statistics are kept from the time the connection is established. That means every time you disconnect or reboot your computer, you reset the networking statistics.
  Accepted .................... : 41   Failed Attempts ............. : 187   Reset ....................... : 2271      Segment Data:   Received  ................... : 334791   Sent ........................ : 263171   Retransmitted ............... : 617

6.3.2. What about...

...other connection problems, like a disconnected router, erratic network, or a firewall that's blocking access to the location you need? The network connection statistics won't give you any information about the rest of the network (although you can try to ping a machine elsewhere on the network, as described in the previous lab, "Ping Another Computer"). In other words, even when a network connection is available there's no way to make sure it's working. For that reason, whenever you need to access a resource over the networkwhether it's a web service, database, or application running on another computeryou need to wrap your call in proper exception-handling code.

6.3.3. Where can I learn more?

For more information on advanced network statistics, look up the "IPGlobalProperties" index entry in the MSDN help, or look for the "network information sample" for a more sophisticated Windows Forms application that monitors network activity.



Visual Basic 2005(c) A Developer's Notebook
Visual Basic 2005: A Developers Notebook
ISBN: 0596007264
EAN: 2147483647
Year: 2006
Pages: 123

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