What is the best way to check for Internet connectivity using NET

Question

What is the fastest and most efficient way to check for Internet connectivity in  NET

User · Answer

You can use NetworkInterface GetIsNetworkAvailable method which indicates whether any network connection is available  Try this  bool connection   NetworkInterface GetIsNetworkAvailable    if  connection    true          MessageBox Show  quot The system is online quot        else        MessageBox Show  quot The system is offline quot

User · Answer

I have seen all the options listed above and the only viable option to check wither the internet is available or not is the  Ping  option  Importing      DllImport  Wininet dll    and  System Net NetworkInformation NetworkInterface GetAllNetworkInterfaces         Or  any other variation of the   NetworkInterface   class does not work well in detecting the availability of the network These Methods only check if the network cable is plugged in or not   The    Ping option   if Connection is available  returns   true  if Connection is not available and the network cable is plugged in  returns          false  if Network cable is not plugged in  Throws an exception  The   NetworkInterface  if Internet Is available Returns True  if Internet is not Available and Network Cable is Plugged in   Returns True  if Network Cable is Not Plugged in  returns false  The     DllImport  Wininet dll     if Internet Is available Returns True  if Internet is not Available and Network Cable is Plugged in   Returns True  if Network Cable is Not Plugged in  returns false  So in case of  DllImport  Wininet dll       and    NetworkInterface     There is no way of knowing if internet connection is available

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I have three tests for an Internet connection    Reference System Net and System Net Sockets Add the following test functions    Test 1  public bool IsOnlineTest1         try               IPHostEntry dummy   Dns GetHostEntry  https   www google com            return true            catch  SocketException ex                return false            Test 2  public bool IsOnlineTest2         try               IPHostEntry dummy   Dns GetHostEntry  https   www google com            return true            catch  SocketException ex                return false            Test 3  public bool IsOnlineTest3         System Net WebRequest req   System Net WebRequest Create  https   www google com        System Net WebResponse resp   default System Net WebResponse       try               resp   req GetResponse            resp Close            req   null          return true            catch  Exception ex                req   null          return false            Performing the tests  If you make a Dictionary of String and Boolean called CheckList  you can add the results of each test to CheckList   Now  recurse through each KeyValuePair using a for   each loop   If CheckList contains a Value of true  then you know there is an Internet connection

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Does not solve the problem of network going down between checking and running your code         but is fairly reliable  public static bool IsAvailableNetworkActive            only recognizes changes related to Internet adapters     if  System Net NetworkInformation NetworkInterface GetIsNetworkAvailable                     however  this will include all adapters -- filter by opstatus and activity         NetworkInterface   interfaces   System Net NetworkInformation NetworkInterface GetAllNetworkInterfaces            return  from face in interfaces                 where face OperationalStatus    OperationalStatus Up                 where  face NetworkInterfaceType    NetworkInterfaceType Tunnel   amp  amp   face NetworkInterfaceType    NetworkInterfaceType Loopback                  select face GetIPv4Statistics    Any statistics   gt   statistics BytesReceived  gt  0   amp  amp   statistics BytesSent  gt  0               return false

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There is absolutely no way you can reliably check if there is an internet connection or not  I assume you mean access to the internet    You can  however  request resources that are virtually never offline  like pinging google com or something similar  I think this would be efficient   try        Ping myPing   new Ping        String host    google com       byte   buffer   new byte 32       int timeout   1000      PingOptions pingOptions   new PingOptions        PingReply reply   myPing Send host  timeout  buffer  pingOptions       return  reply Status    IPStatus Success     catch  Exception        return false

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public static bool HasConnection         try               System Net IPHostEntry i   System Net Dns GetHostEntry  www google com            return true            catch               return false            That works

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I disagree with people who are stating   What s the point in checking for connectivity before performing a task  as immediately after the check the connection may be lost   Surely there is a degree of uncertainty in many programming tasks we as developers undertake  but reducing the uncertainty to a level of acceptance is part of the challenge   I recently ran into this problem making an application which including a mapping feature which linked to an on-line tile server  This functionality was to be disabled where a lack of internet connectivity was noted   Some of the responses on this page were very good  but did however cause a lot of performance issues such as hanging  mainly in the case of the absence of connectivity   Here is the solution that I ended up using  with the help of some of these answers and my colleagues               Insert this where check is required  in my case program start          ThreadPool QueueUserWorkItem CheckInternetConnectivity              void CheckInternetConnectivity object state                if  System Net NetworkInformation NetworkInterface GetIsNetworkAvailable                          using  WebClient webClient   new WebClient                                  webClient CachePolicy   new System Net Cache RequestCachePolicy System Net Cache RequestCacheLevel BypassCache                   webClient Proxy   null                  webClient OpenReadCompleted    webClient OpenReadCompleted                  webClient OpenReadAsync new Uri   lt url of choice here gt                                         volatile bool internetAvailable   false     boolean used elsewhere in code      void webClient OpenReadCompleted object sender  OpenReadCompletedEventArgs e                if  e Error    null                        internetAvailable   true              Dispatcher Invoke DispatcherPriority Normal  new Action      gt                                   UI changes made here

User · Answer

private bool ping         System Net NetworkInformation Ping pingSender   new System Net NetworkInformation Ping        System Net NetworkInformation PingReply reply   pingSender Send address       if  reply Status    System Net NetworkInformation IPStatus Success                                return true            else                               return false

User · Answer

public static bool Isconnected   false   public static bool CheckForInternetConnection         try               Ping myPing   new Ping            String host    google com           byte   buffer   new byte 32           int timeout   1000          PingOptions pingOptions   new PingOptions            PingReply reply   myPing Send host  timeout  buffer  pingOptions           if  reply Status    IPStatus Success                        return true                    else if  reply Status    IPStatus TimedOut                        return Isconnected                    else                       return false                      catch  Exception                return false           public static void CheckConnection         if  CheckForInternetConnection                  Isconnected   true            else               Isconnected   false

User · Answer

Instead of checking  just perform the action  web request  mail  ftp  etc   and be prepared for the request to fail  which you have to do anyway  even if your check was successful   Consider the following   1 - check  and it is OK 2 - start to perform action  3 - network goes down 4 - action fails 5 - lot of good your check did   If the network is down your action will fail just as rapidly as a ping  etc     1 - start to perform action 2 - if the net is down or goes down  the action will fail

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Here s how it is implemented in Android   As a proof of concept  I translated this code to C    var request    HttpWebRequest WebRequest Create  http   g cn generate 204    request UserAgent    Android   request KeepAlive   false  request Timeout   1500   using  var response    HttpWebResponse request GetResponse          if  response ContentLength    0  amp  amp  response StatusCode    HttpStatusCode NoContent                  Connection to internet available           else                 Connection to internet not available

User · Answer

Something like this should work   System Net WebClient  public static bool CheckForInternetConnection         try               using  var client   new WebClient                using  client OpenRead  http   google com generate 204                     return true             catch               return false

User · Answer

Introduction  In some scenarios you need to check whether internet is available or not using C  code in windows applications  May be to download or upload a file using internet in windows forms or to get some data from database which is at remote location  in these situations internet check is compulsory   There are some ways to check internet availability using C  from code behind  All such ways are explained here including their limitations    InternetGetConnectedState wininet    The  wininet  API can be used to check the local system has active internet connection or not  The namespace used for this is  System Runtime InteropServices  and import the dll  wininet dll  using DllImport  After this create a boolean variable with extern static with a function name InternetGetConnectedState with two parameters description and reservedValue as shown in example   Note  The extern modifier is used to declare a method that is implemented externally  A common use of the extern modifier is with the DllImport attribute when you are using Interop services to call into unmanaged code  In this case  the method must also be declared as static      Next create a method with name  IsInternetAvailable  as boolean  The   above function will be used in this method which returns internet   status of local system    DllImport  wininet dll    private extern static bool InternetGetConnectedState out int description  int reservedValue   public static bool IsInternetAvailable         try               int description          return InternetGetConnectedState out description  0             catch  Exception ex                return false             GetIsNetworkAvailable   The following example uses the GetIsNetworkAvailable method to determine if a network connection is available   if  System Net NetworkInformation NetworkInterface GetIsNetworkAvailable          System Windows MessageBox Show  This computer is connected to the internet      else       System Windows MessageBox Show  This computer is not connected to the internet        Remarks  As per MSDN   A network connection is considered to be available if any network interface is marked  up  and is not a loopback or tunnel interface   There are many cases in which a device or computer is not connected to a useful network but is still considered available and GetIsNetworkAvailable will return true  For example  if the device running the application is connected to a wireless network that requires a proxy  but the proxy is not set  GetIsNetworkAvailable will return true  Another example of when GetIsNetworkAvailable will return true is if the application is running on a computer that is connected to a hub or router where the hub or router has lost the upstream connection    Ping a hostname on the network   Ping and PingReply classes allows an application to determine whether a remote computer is accessible over the network by getting reply from the host  These classes are available in System Net NetworkInformation namespace  The following example shows how to ping a host   protected bool CheckConnectivity string ipAddress        bool connectionExists   false      try               System Net NetworkInformation Ping pingSender   new System Net NetworkInformation Ping            System Net NetworkInformation PingOptions options   new System Net NetworkInformation PingOptions            options DontFragment   true          if   string IsNullOrEmpty ipAddress                         System Net NetworkInformation PingReply reply   pingSender Send ipAddress               connectionExists   reply Status     System Net NetworkInformation IPStatus Success   true   false                      catch  PingException ex                Logger LogException ex Message  ex             return connectionExists      Remarks  As per MSDN   Applications use the Ping class to detect whether a remote computer is reachable  Network topology can determine whether Ping can successfully contact a remote host  The presence and configuration of proxies  network address translation  NAT  equipment  or firewalls can prevent Ping from succeeding  A successful Ping indicates only that the remote host can be reached on the network  the presence of higher level services  such as a Web server  on the remote host is not guaranteed   Comments Suggestions are invited  Happy coding

User · Answer

For my application we also test by download tiny file   string remoteUri    https   www microsoft com favicon ico   WebClient myWebClient   new WebClient     try       byte   myDataBuffer   myWebClient DownloadData  remoteUri       if myDataBuffer length  gt  0     Or add more validate  eg  checksum               return true          catch       return false      Also  Some ISP may use middle server to cache file  Add random unused parameter eg  https   www microsoft com favicon ico req random number Can prevent caching

User · Answer

I personally find the answer of Anton and moffeltje best  but I added a check to exclude virtual networks set up by VMWare and others   public static bool IsAvailableNetworkActive            only recognizes changes related to Internet adapters     if   System Net NetworkInformation NetworkInterface GetIsNetworkAvailable    return false          however  this will include all adapters -- filter by opstatus and activity     NetworkInterface   interfaces   System Net NetworkInformation NetworkInterface GetAllNetworkInterfaces        return  from face in interfaces             where face OperationalStatus    OperationalStatus Up             where  face NetworkInterfaceType    NetworkInterfaceType Tunnel   amp  amp   face NetworkInterfaceType    NetworkInterfaceType Loopback              where    face Name ToLower   Contains  virtual      face Description ToLower   Contains  virtual                 select face GetIPv4Statistics    Any statistics   gt   statistics BytesReceived  gt  0   amp  amp   statistics BytesSent  gt  0

User · Answer

Pinging google com introduces a DNS resolution dependency  Pinging 8 8 8 8 is fine but Google is several hops away from me  All I need to do is to ping the nearest thing to me that is on the internet    I can use Ping s TTL feature to ping hop  1  then hop  2  etc  until I get a reply from something that is on a routable address  if that node is on a routable address then it is on the internet   For most of us  hop  1 will be our local gateway router  and hop  2 will be the first point on the other side of our fibre connection or whatever     This code works for me  and responds quicker than some of the other suggestions in this thread because it is pinging whatever is nearest to me on the internet   using System Net  using System Net Sockets  using System Net NetworkInformation  using System Diagnostics   internal static bool ConnectedToInternet         const int maxHops   30      const string someFarAwayIpAddress    8 8 8 8           Keep pinging further along the line from here to google         until we find a response that is from a routable address     for  int ttl   1  ttl  lt   maxHops  ttl                  Ping pinger   new Ping            PingOptions options   new PingOptions ttl  true           byte   buffer   new byte 32           PingReply reply   null          try                       reply   pinger Send someFarAwayIpAddress  10000  buffer  options                     catch  System Net NetworkInformation PingException pingex                        Debug Print  Ping exception  probably due to no network connection or recent change in network conditions   hence not connected to internet  Message      pingex Message               return false                     System Diagnostics Debug Print  Hop      ttl ToString       is      reply Address    null    null    reply Address ToString             reply Status ToString              if  reply Status    IPStatus TtlExpired  amp  amp  reply Status    IPStatus Success                        Debug Print  Hop      ttl ToString       is     reply Status ToString        hence we are not connected                 return false                     if  IsRoutableAddress reply Address                         System Diagnostics Debug Print  That s routable so you must be connected to the internet                 return true                       return false     private static bool IsRoutableAddress IPAddress addr        if  addr    null                return false            else if  addr AddressFamily    AddressFamily InterNetworkV6                return  addr IsIPv6LinkLocal  amp  amp   addr IsIPv6SiteLocal            else    IPv4               byte   bytes   addr GetAddressBytes            if  bytes 0     10                 Class A network             return false                    else if  bytes 0     172  amp  amp  bytes 1   gt   16  amp  amp  bytes 1   lt   31                 Class B network             return false                    else if  bytes 0     192  amp  amp  bytes 1     168                 Class C network             return false                    else                None of the above  so must be routable             return true

User · Answer

Try to avoid testing connections by catching the exception  because we really Expect that sometimes we may lose network connection    if  NetworkInterface GetIsNetworkAvailable    amp  amp       new Ping   Send new IPAddress new byte     8  8  8  8    2000  Status    IPStatus Success     is online  else    is offline

User · Answer

I am having issue on those method on my 3g Router modem  because if internet is disconnected the router redirects the page to its response page  so you still get a steam and your code think there is internet  Apples  or others  have a hot-spot-dedection page which always returns a certain response  The following sample returns  Success  response  So you will be exactly sure you could connect the internet and get real response    public static bool CheckForInternetConnection         try                      using  var webClient   new WebClient            using  var stream   webClient OpenRead  http   captive apple com hotspot-detect html                          if  stream    null                                  return true                  stream ReadTimeout   1000                  using  var reader   new StreamReader stream  Encoding UTF8  false                                         string line                      while   line   reader ReadLine       null                                                if  line      lt HTML gt  lt HEAD gt  lt TITLE gt Success lt  TITLE gt  lt  HEAD gt  lt BODY gt Success lt  BODY gt  lt  HTML gt                                                          return true                                                    Console WriteLine line                                                                      return false                      catch                  return false

User · Answer

The accepted answer succeeds quickly but is very slow to fail when there is no connection  So I wanted to build a robust connection check that would fail faster  Pinging was said to not be supported in all environments  so I started with the accepted answer and added a WebClient from here with a custom timeout  You can pick any timeout  but 3 seconds worked for me while connected via wifi  I tried adding a fast iteration  1 second   then a slow iteration  3 seconds  if the first one fails  But that made no sense since both iterations would always fail  when not connected  or always succeed  when connected   I m connecting to AWS since I want to upload a file when the connection test passes  public static class AwsHelpers       public static bool GetCanConnectToAws                 try                       using  var client   new WebClientWithShortTimeout                using  client OpenRead  quot https   aws amazon com quot                    return true                    catch                       return false                     public class WebClientWithShortTimeout  WebClient       protected override WebRequest GetWebRequest Uri uri                var webRequest   base GetWebRequest uri           webRequest Timeout   5000          return webRequest

User · Answer

I wouldn t think it s impossible  just not straightforward   I ve built something like this  and yes it s not perfect  but the first step is essential  to check if there s any network connectivity  The Windows Api doesn t do a great job  so why not do a better job   bool NetworkIsAvailable         var all   System Net NetworkInformation NetworkInterface GetAllNetworkInterfaces        foreach  var item in all                if  item NetworkInterfaceType    NetworkInterfaceType Loopback              continue          if  item Name ToLower   Contains  virtual      item Description ToLower   Contains  virtual                continue    Exclude virtual networks set up by VMWare and others         if  item OperationalStatus    OperationalStatus Up                        return true                       return false      It s pretty simple  but it really helps improve the quality of the check  especially when you want to check various proxy configurations    So    Check whether there s network connectivity  make this really good  maybe even have logs sent back to developers when there are false positives to improve the NetworkIsAvailable function  HTTP Ping  Cycle through Proxy configurations with HTTP Pings on each

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Multi threaded version of ping     using System    using System Collections Generic    using System Diagnostics    using System Net NetworkInformation    using System Threading      namespace OnlineCheck           class Program                    static bool isOnline   false             static void Main string   args                            List lt string gt  ipList   new List lt string gt                       1 1 1 1      Bad ip                    2 2 2 2                      4 2 2 2                      8 8 8 8                      9 9 9 9                      208 67 222 222                      139 130 4 5                                      int timeOut   1000   5     Seconds                 List lt Thread gt  threadList   new List lt Thread gt                    foreach  string ip in ipList                                     Thread threadTest   new Thread      gt  IsOnline ip                      threadList Add threadTest                     threadTest Start                                   Stopwatch stopwatch   Stopwatch StartNew                   while   isOnline  amp  amp  stopwatch ElapsedMilliseconds  lt   timeOut                                     Thread Sleep 10      Cooldown the CPU                                foreach  Thread thread in threadList                                     thread Abort       We love threads  don t we                                  Console WriteLine  Am I online      isOnline ToYesNo                   Console ReadKey                           static bool Ping string host  int timeout   3000  int buffer   32                            bool result   false                 try                                   Ping ping   new Ping                                      byte   byteBuffer   new byte buffer                                     PingOptions options   new PingOptions                      PingReply reply   ping Send host  timeout  byteBuffer  options                     result    reply Status    IPStatus Success                                 catch  Exception ex                                                  return result                         static void IsOnline string host                            isOnline    Ping host     isOnline                             public static class BooleanExtensions                   public static string ToYesNo this bool value                            return value    Yes     No

User · Answer

NetworkInterface GetIsNetworkAvailable is very unreliable  Just have some VMware or other LAN connection and it will return wrong result  Also about Dns GetHostEntry method I were just concerned about whether test URL might be blocked in the environment where my application going to deploy   So another way I found out is using InternetGetConnectedState method  My code is    System Runtime InteropServices DllImport  wininet dll    private extern static bool InternetGetConnectedState out int Description  int ReservedValue    public static bool CheckNet          int desc       return InternetGetConnectedState out desc  0

User · Answer

If you want to notify the user take action whenever a network connection change occur  Use NLM API    https   msdn microsoft com en-us library ee264321 aspx http   www codeproject com Articles 34650 How-to-use-the-Windows-NLM-API-to-get-notified-of

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A test for internet connection by pinging Google   new Ping   Send  www google com mx   Status    IPStatus Success

User · Answer

Another option is the Network List Manager API which is available for Vista and Windows 7  MSDN article here  In the article is a link to download code samples which allow you to do this   AppNetworkListUser nlmUser   new AppNetworkListUser    Console WriteLine  Is the machine connected to internet      nlmUser NLM IsConnectedToInternet ToString       Be sure to add a reference to Network List 1 0 Type Library from the COM tab    which will show up as NETWORKLIST

User · Answer

bool bb   System Net NetworkInformation NetworkInterface GetIsNetworkAvailable     if  bb    true      MessageBox Show  Internet connections are available    else     MessageBox Show  Internet connections are not available

User · Answer

Use NetworkMonitor to monitoring network state and internet connection   Sample   namespace AmRoNetworkMonitor Demo       using System       internal class Program               private static void Main                         NetworkMonitor StateChanged    NetworkMonitor StateChanged              NetworkMonitor StartMonitor                 Console WriteLine  Press any key to stop monitoring                 Console ReadKey                NetworkMonitor StopMonitor                 Console WriteLine  Press any key to close program                 Console ReadKey                       private static void NetworkMonitor StateChanged object sender  StateChangeEventArgs e                        Console WriteLine e IsAvailable    Is Available     Is Not Available

[c#] What is the best way to check for Internet connectivity using .NET?

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