How do I check for a network connection

Question

What is the best way to determine if there is a network connection available

User · Accepted Answer

You can check for a network connection in .NET 2.0 using GetIsNetworkAvailable():

System.Net.NetworkInformation.NetworkInterface.GetIsNetworkAvailable()

To monitor changes in IP address or changes in network availability use the events from the NetworkChange class:

System.Net.NetworkInformation.NetworkChange.NetworkAvailabilityChanged
System.Net.NetworkInformation.NetworkChange.NetworkAddressChanged

User · Answer

Call this method to check the network Connection   public static bool IsConnectedToInternet                         bool returnValue   false              try                                int Desc                  returnValue   Utility InternetGetConnectedState out Desc  0                             catch                               returnValue   false                            return returnValue              Put this below line of code    DllImport  wininet dll            public extern static bool InternetGetConnectedState out int Description  int ReservedValue

User · Answer

The marked answer is 100  fine  however  there are certain cases when the standard method is fooled by virtual cards  virtual box        It s also often desirable to discard some network interfaces based on their speed  serial ports  modems         Here is a piece of code that checks for these cases            lt summary gt          Indicates whether any network connection is available         Filter connections below a specified speed  as well as virtual network cards           lt  summary gt           lt returns gt               lt c gt true lt  c gt  if a network connection is available  otherwise   lt c gt false lt  c gt            lt  returns gt      public static bool IsNetworkAvailable                 return IsNetworkAvailable 0                   lt summary gt          Indicates whether any network connection is available          Filter connections below a specified speed  as well as virtual network cards           lt  summary gt           lt param name  minimumSpeed  gt The minimum speed required  Passing 0 will not filter connection using speed  lt  param gt           lt returns gt               lt c gt true lt  c gt  if a network connection is available  otherwise   lt c gt false lt  c gt            lt  returns gt      public static bool IsNetworkAvailable long minimumSpeed                if   NetworkInterface GetIsNetworkAvailable                return false           foreach  NetworkInterface ni in NetworkInterface GetAllNetworkInterfaces                             discard because of standard reasons             if   ni OperationalStatus    OperationalStatus Up                      ni NetworkInterfaceType    NetworkInterfaceType Loopback                      ni NetworkInterfaceType    NetworkInterfaceType Tunnel                   continue                  this allow to filter modems  serial  etc                 I use 10000000 as a minimum speed for most cases             if  ni Speed  lt  minimumSpeed                  continue                  discard virtual cards  virtual box  virtual pc  etc               if   ni Description IndexOf  virtual   StringComparison OrdinalIgnoreCase   gt   0                      ni Name IndexOf  virtual   StringComparison OrdinalIgnoreCase   gt   0                   continue                  discard  Microsoft Loopback Adapter   it will not show as NetworkInterfaceType Loopback but as Ethernet Card              if  ni Description Equals  Microsoft Loopback Adapter   StringComparison OrdinalIgnoreCase                   continue               return true                    return false

User · Answer

Microsoft windows vista and 7 use NCSI  Network Connectivity Status Indicator  technic    NCSI performs a DNS lookup on www msftncsi com  then requests http   www msftncsi com ncsi txt  This file is a plain-text file and contains only the text  Microsoft NCSI   NCSI sends a DNS lookup request for dns msftncsi com  This DNS address should resolve to 131 107 255 255  If the address does not match  then it is assumed that the internet connection is not functioning correctly

[c#] How do I check for a network connection?

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