为什么 Ping 超时无法正常工作？
Why Ping timeout is not working correctly?
我有 5 台电脑，我想 ping 这台电脑是否可用。所以我正在使用 c# Ping class。有两台电脑可用，但当我对它们执行 ping 命令时，其他 3 台电脑已关闭我的程序等待 7 秒以内响应。
我只想检查 1000 毫秒和 returns OK 或 ERROR...
如何控制 ping 超时？
这是我的代码
foreach (var item in listofpc)
{
Stopwatch timer = Stopwatch.StartNew();
try
{
Ping myPing = new Ping();
PingReply reply = myPing.Send(ServerName, 500);
if (reply != null)
{
timer.Stop();
TimeSpan timeTaken = timer.Elapsed;
Log.append("PING OK TimeTaken="+ timeTaken.ToString() + " Miliseconds", 50);
}
}
catch (Exception ex)
{
timer.Stop();
TimeSpan timeTaken = timer.Elapsed;
Log.append("PING ERROR TimeTaken=" +
timeTaken.ToString() + " Miliseconds \n" + ex.ToString(), 50);
}
}
但是当我查看我的日志时，我看到响应时间是 2 秒。为什么 ping 超时值不起作用？
有什么想法吗？
更新：原因：正如其他人所说，Ping 超时不起作用的最可能原因是 DNS 解析。对 getaddrinfo 的系统调用（Dns.GetHostAddresses 和 Ping - https://docs.microsoft.com/en-us/windows/win32/api/ws2tcpip/nf-ws2tcpip-getaddrinfo, https://docs.microsoft.com/en-us/dotnet/api/system.net.dns.gethostaddresses?view=netcore-3.1 使用的系统调用 - 类似于 Full Framework）不接受超时。因此，对下面代码的进一步改进是将 dns 查找与 ping 分开。首先使用类似于下面代码的超时方法进行查找，并且仅 ping IP 而不是主机名，并指定超时。
我过去 运行 遇到过类似的问题，我有一些代码可能有助于解决这个问题。我在这里编辑它，所以它可能不是 100% 正确，并且比您的需要复杂一点。你能试试这样的吗？
锤子：（下面还包含带有测试结果的完整代码）
private static PingReply ForcePingTimeoutWithThreads(string hostname, int timeout)
{
PingReply reply = null;
var a = new Thread(() => reply = normalPing(hostname, timeout));
a.Start();
a.Join(timeout); //or a.Abort() after a timeout, but you have to take care of a ThreadAbortException in that case... brrr I like to think that the ping might go on and be successful in life with .Join :)
return reply;
}
private static PingReply normalPing(string hostname, int timeout)
{
try
{
return new Ping().Send(hostname, timeout);
}
catch //never do this kids, this is just a demo of a concept! Always log exceptions!
{
return null; //or this, in such a low level method 99 cases out of 100, just let the exception bubble up
}
}
这是一个完整的工作示例（Tasks.WhenAny 测试并在版本 4.5.2 中工作）。我还了解到，Tasks 的优雅带来了比我记忆中更显着的性能损失，但是 Thread.Join/Abort 对于大多数生产环境来说太残酷了。
using System;
using System.Diagnostics;
using System.Net.NetworkInformation;
using System.Threading;
using System.Threading.Tasks;
namespace ConsoleApp1
{
class Program
{
//this can easily be async Task<PingReply> or even made generic (original version was), but I wanted to be able to test all versions with the same code
private static PingReply PingOrTimeout(string hostname, int timeOut)
{
PingReply result = null;
var cancellationTokenSource = new CancellationTokenSource();
var timeoutTask = Task.Delay(timeOut, cancellationTokenSource.Token);
var actionTask = Task.Factory.StartNew(() =>
{
result = normalPing(hostname, timeOut);
}, cancellationTokenSource.Token);
Task.WhenAny(actionTask, timeoutTask).ContinueWith(t =>
{
cancellationTokenSource.Cancel();
}).Wait(); //if async, remove the .Wait() and await instead!
return result;
}
private static PingReply normalPing(string hostname, int timeout)
{
try
{
return new Ping().Send(hostname, timeout);
}
catch //never do this kids, this is just a demo of a concept! Always log exceptions!
{
return null; //or this, in such a low level method 99 cases out of 100, just let the exception bubble up
}
}
private static PingReply ForcePingTimeoutWithThreads(string hostname, int timeout)
{
PingReply reply = null;
var a = new Thread(() => reply = normalPing(hostname, timeout));
a.Start();
a.Join(timeout); //or a.Abort() after a timeout... brrr I like to think that the ping might go on and be successful in life with .Join :)
return reply;
}
static byte[] b = new byte[32];
static PingOptions po = new PingOptions(64, true);
static PingReply JimiPing(string hostname, int timeout)
{
try
{
return new Ping().Send(hostname, timeout, b, po);
}
catch //never do this kids, this is just a demo of a concept! Always log exceptions!
{
return null; //or this, in such a low level method 99 cases out of 100, just let the exception bubble up
}
}
static void RunTests(Func<string, int, PingReply> timeOutPinger)
{
var stopWatch = Stopwatch.StartNew();
var expectedFail = timeOutPinger("bogusdjfkhkjh", 200);
Console.WriteLine($"{stopWatch.Elapsed.TotalMilliseconds} false={expectedFail != null}");
stopWatch = Stopwatch.StartNew();
var expectedSuccess = timeOutPinger("127.0.0.1", 200);
Console.WriteLine($"{stopWatch.Elapsed.TotalMilliseconds} true={expectedSuccess != null && expectedSuccess.Status == IPStatus.Success}");
}
static void Main(string[] args)
{
RunTests(normalPing);
RunTests(PingOrTimeout);
RunTests(ForcePingTimeoutWithThreads);
RunTests(JimiPing);
Console.ReadKey(false);
}
}
}
我的一些测试结果：
>Running ping timeout tests timeout = 200. method=normal
>
> - host: bogusdjfkhkjh elapsed: 2366,9714 expected: false=False
> - host: 127.0.0.1 elapsed: 4,7249 expected: true=True
>
>Running ping timeout tests timeout = 200. method:ttl+donotfragment (Jimi)
>
> - host: bogusdjfkhkjh elapsed: 2310,836 expected: false actual: False
> - host: 127.0.0.1 elapsed: 0,7838 expected: true actual: True
>
>Running ping timeout tests timeout = 200. method:tasks
>
> - host: bogusdjfkhkjh elapsed: 234,1491 expected: false actual: False
> - host: 127.0.0.1 elapsed: 3,2829 expected: true=True
>
>Running ping timeout tests timeout = 200. method:threads
>
> - host: bogusdjfkhkjh elapsed: 200,5357 expected: false actual:False
> - host: 127.0.0.1 elapsed: 5,5956 expected: true actual: True
警告 对于任务版本，即使调用线程“未阻塞”，操作本身（在本例中为 ping）也可能会持续到实际超时为止。这就是为什么我建议也为 ping 命令本身设置超时。
更新 也在研究原因，但认为解决方法暂时可以帮助您。
新发现：
此 System.Net.NetworkInformation.Ping 的实施已通过
测试
框架 4.0/4.5.1/4.7.1，控制台和 Winforms 版本。
结果始终相同（如下所述）。
这是 IcmpSendEcho2 和 Icmp6SendEcho2
的 .NET Framework Ping() 实现
同步版本（输出类型为Console，但不相关）：
(The original version of this method does not return IPStatus. It
returns a Class Object with full exception information. The Host Name
or address is verified/translated with the DNS resolver:
IPAddress _HostIPAddress = Dns.GetHostAddresses(HostAddress).First(); which throws a SocketException if the Host is not found and a No such host is known notification.
The Result: BadDestination for an unknown host is set here just for this test).
static void Main(string[] args)
{
List<string> HostAdrr = new List<string>() { "192.168.2.1", "192.168.2.201",
"192.168.1.99", "200.1.1.1",
"www.microsoft.com", "www.hfkhkhfhkf.com" };
IPStatus _result;;
foreach (string _Host in HostAdrr)
{
Stopwatch timer = Stopwatch.StartNew();
_result = PingHostAddress(_Host, 1000);
timer.Stop();
Console.WriteLine("Host: {0} Elapsed time: {1}ms Result: {2}", _Host, timer.ElapsedMilliseconds, _result);
Console.WriteLine();
}
Console.ReadLine();
}
public static IPStatus PingHostAddress(string HostAddress, int timeout)
{
if (string.IsNullOrEmpty(HostAddress.Trim()))
return IPStatus.BadDestination;
byte[] buffer = new byte[32];
PingReply iReplay = null;
using (Ping iPing = new Ping())
{
try
{
//IPAddress _HostIPAddress = Dns.GetHostAddresses(HostAddress).First();
iReplay = iPing.Send(HostAddress,
timeout,
buffer,
new PingOptions(64, true));
}
catch (FormatException)
{
return IPStatus.BadDestination;
}
catch (NotSupportedException nsex)
{
throw nsex;
}
catch (PingException pex)
{
//Log/Manage pex
}
//catch (SocketException soex)
//{
//
//}
catch (Exception ex)
{
//Log/Manage ex
}
return (iReplay != null) ? iReplay.Status : IPStatus.BadDestination;
}
}
异步版本使用.SendPingAsync()方法并具有通常的异步签名。
public async Task<IPStatus> PingHostAddressAsync(string HostAddress, int timeout)
{
//(...)
iReplay = await iPing.SendPingAsync(HostAddress,
timeout,
buffer,
new PingOptions(64, false));
//(...)
}
使用异步版本时结果不会改变。使用 Winforms 测试。不管有多少人想弄乱 UI.
如何解读结果：
参数：
- 由 Ping.Send() 方法解析的主机名。 （预先解析主机名不会改变结果）
- 超时： 1000 毫秒（还测试了 500 毫秒和 2000 毫秒）
- 缓冲区： 标准 32 字节
- TTL: 64
- 不要分段： 正确
Host: 192.168.2.1 => Reachable Host in the same network.
Host: 192.168.2.201 => Unreachable (off) Host in a reachable
different subnet.
Host: 192.168.1.99 => Non existent Host in a reachable different network (hardware routed)
Host: 200.1.1.1 => Non existent Internet Address
Host: www.microsoft.com => Reachable existing resolved Internet Host Name
Host: www.hfkhkhfhkf.com => Non existent unresolvable Internet Host Name
Host: 192.168.2.1 Elapsed time: 4 Result: Success
Host: 192.168.2.201 Elapsed time: 991 Result: TimedOut
Host: 192.168.1.99 Elapsed time: 993 Result: TimedOut
Host: 200.1.1.1 Elapsed time: 997 Result: TimedOut
Host: www.microsoft.com Elapsed time: 57 Result: Success
Host: www.hfkhkhfhkf.com Elapsed time: 72 Result: BadDestination
As also noted by @PaulF in the comments, the only (persistent) anomaly
is the first response if the Host is unreachable: it's always a bit
shorter than the imposed timeout. But the Timeout is always respected (the Ping method always returns within the set time interval).
Ping 到 8.8.8.8 这样的 IP 地址绝对没问题，但是当 ping 到像 www.google.com 这样的 dns 地址时，随机超时。
我认为这些随机超时与 dns 解析有关，与 ping 超时无关
private static bool DoPing()
{
try
{
using (System.Net.NetworkInformation.Ping ping = new Ping())
{
PingReply result = ping.Send("8.8.8.8", 500, new byte[32], new PingOptions { DontFragment = true, Ttl = 32 });
if (result.Status == IPStatus.Success)
return true;
return false;
}
}
catch
{
return false;
}
}
我有 5 台电脑，我想 ping 这台电脑是否可用。所以我正在使用 c# Ping class。有两台电脑可用，但当我对它们执行 ping 命令时，其他 3 台电脑已关闭我的程序等待 7 秒以内响应。
我只想检查 1000 毫秒和 returns OK 或 ERROR...
如何控制 ping 超时？
这是我的代码
foreach (var item in listofpc)
{
Stopwatch timer = Stopwatch.StartNew();
try
{
Ping myPing = new Ping();
PingReply reply = myPing.Send(ServerName, 500);
if (reply != null)
{
timer.Stop();
TimeSpan timeTaken = timer.Elapsed;
Log.append("PING OK TimeTaken="+ timeTaken.ToString() + " Miliseconds", 50);
}
}
catch (Exception ex)
{
timer.Stop();
TimeSpan timeTaken = timer.Elapsed;
Log.append("PING ERROR TimeTaken=" +
timeTaken.ToString() + " Miliseconds \n" + ex.ToString(), 50);
}
}
但是当我查看我的日志时，我看到响应时间是 2 秒。为什么 ping 超时值不起作用？
有什么想法吗？
更新：原因：正如其他人所说，Ping 超时不起作用的最可能原因是 DNS 解析。对 getaddrinfo 的系统调用（Dns.GetHostAddresses 和 Ping - https://docs.microsoft.com/en-us/windows/win32/api/ws2tcpip/nf-ws2tcpip-getaddrinfo, https://docs.microsoft.com/en-us/dotnet/api/system.net.dns.gethostaddresses?view=netcore-3.1 使用的系统调用 - 类似于 Full Framework）不接受超时。因此，对下面代码的进一步改进是将 dns 查找与 ping 分开。首先使用类似于下面代码的超时方法进行查找，并且仅 ping IP 而不是主机名，并指定超时。
我过去 运行 遇到过类似的问题，我有一些代码可能有助于解决这个问题。我在这里编辑它，所以它可能不是 100% 正确，并且比您的需要复杂一点。你能试试这样的吗？
锤子：（下面还包含带有测试结果的完整代码）
private static PingReply ForcePingTimeoutWithThreads(string hostname, int timeout)
{
PingReply reply = null;
var a = new Thread(() => reply = normalPing(hostname, timeout));
a.Start();
a.Join(timeout); //or a.Abort() after a timeout, but you have to take care of a ThreadAbortException in that case... brrr I like to think that the ping might go on and be successful in life with .Join :)
return reply;
}
private static PingReply normalPing(string hostname, int timeout)
{
try
{
return new Ping().Send(hostname, timeout);
}
catch //never do this kids, this is just a demo of a concept! Always log exceptions!
{
return null; //or this, in such a low level method 99 cases out of 100, just let the exception bubble up
}
}
这是一个完整的工作示例（Tasks.WhenAny 测试并在版本 4.5.2 中工作）。我还了解到，Tasks 的优雅带来了比我记忆中更显着的性能损失，但是 Thread.Join/Abort 对于大多数生产环境来说太残酷了。
using System;
using System.Diagnostics;
using System.Net.NetworkInformation;
using System.Threading;
using System.Threading.Tasks;
namespace ConsoleApp1
{
class Program
{
//this can easily be async Task<PingReply> or even made generic (original version was), but I wanted to be able to test all versions with the same code
private static PingReply PingOrTimeout(string hostname, int timeOut)
{
PingReply result = null;
var cancellationTokenSource = new CancellationTokenSource();
var timeoutTask = Task.Delay(timeOut, cancellationTokenSource.Token);
var actionTask = Task.Factory.StartNew(() =>
{
result = normalPing(hostname, timeOut);
}, cancellationTokenSource.Token);
Task.WhenAny(actionTask, timeoutTask).ContinueWith(t =>
{
cancellationTokenSource.Cancel();
}).Wait(); //if async, remove the .Wait() and await instead!
return result;
}
private static PingReply normalPing(string hostname, int timeout)
{
try
{
return new Ping().Send(hostname, timeout);
}
catch //never do this kids, this is just a demo of a concept! Always log exceptions!
{
return null; //or this, in such a low level method 99 cases out of 100, just let the exception bubble up
}
}
private static PingReply ForcePingTimeoutWithThreads(string hostname, int timeout)
{
PingReply reply = null;
var a = new Thread(() => reply = normalPing(hostname, timeout));
a.Start();
a.Join(timeout); //or a.Abort() after a timeout... brrr I like to think that the ping might go on and be successful in life with .Join :)
return reply;
}
static byte[] b = new byte[32];
static PingOptions po = new PingOptions(64, true);
static PingReply JimiPing(string hostname, int timeout)
{
try
{
return new Ping().Send(hostname, timeout, b, po);
}
catch //never do this kids, this is just a demo of a concept! Always log exceptions!
{
return null; //or this, in such a low level method 99 cases out of 100, just let the exception bubble up
}
}
static void RunTests(Func<string, int, PingReply> timeOutPinger)
{
var stopWatch = Stopwatch.StartNew();
var expectedFail = timeOutPinger("bogusdjfkhkjh", 200);
Console.WriteLine($"{stopWatch.Elapsed.TotalMilliseconds} false={expectedFail != null}");
stopWatch = Stopwatch.StartNew();
var expectedSuccess = timeOutPinger("127.0.0.1", 200);
Console.WriteLine($"{stopWatch.Elapsed.TotalMilliseconds} true={expectedSuccess != null && expectedSuccess.Status == IPStatus.Success}");
}
static void Main(string[] args)
{
RunTests(normalPing);
RunTests(PingOrTimeout);
RunTests(ForcePingTimeoutWithThreads);
RunTests(JimiPing);
Console.ReadKey(false);
}
}
}
我的一些测试结果：
>Running ping timeout tests timeout = 200. method=normal
>
> - host: bogusdjfkhkjh elapsed: 2366,9714 expected: false=False
> - host: 127.0.0.1 elapsed: 4,7249 expected: true=True
>
>Running ping timeout tests timeout = 200. method:ttl+donotfragment (Jimi)
>
> - host: bogusdjfkhkjh elapsed: 2310,836 expected: false actual: False
> - host: 127.0.0.1 elapsed: 0,7838 expected: true actual: True
>
>Running ping timeout tests timeout = 200. method:tasks
>
> - host: bogusdjfkhkjh elapsed: 234,1491 expected: false actual: False
> - host: 127.0.0.1 elapsed: 3,2829 expected: true=True
>
>Running ping timeout tests timeout = 200. method:threads
>
> - host: bogusdjfkhkjh elapsed: 200,5357 expected: false actual:False
> - host: 127.0.0.1 elapsed: 5,5956 expected: true actual: True
警告 对于任务版本，即使调用线程“未阻塞”，操作本身（在本例中为 ping）也可能会持续到实际超时为止。这就是为什么我建议也为 ping 命令本身设置超时。
更新 也在研究原因，但认为解决方法暂时可以帮助您。
新发现：
此 System.Net.NetworkInformation.Ping 的实施已通过
测试
框架 4.0/4.5.1/4.7.1，控制台和 Winforms 版本。
结果始终相同（如下所述）。
这是 IcmpSendEcho2 和 Icmp6SendEcho2
Ping() 实现
同步版本（输出类型为Console，但不相关）：
(The original version of this method does not return
IPStatus. It returns a Class Object with full exception information. The Host Name or address is verified/translated with the DNS resolver:
IPAddress _HostIPAddress = Dns.GetHostAddresses(HostAddress).First();which throws aSocketExceptionif the Host is not found and a No such host is known notification.
The Result: BadDestination for an unknown host is set here just for this test).
static void Main(string[] args)
{
List<string> HostAdrr = new List<string>() { "192.168.2.1", "192.168.2.201",
"192.168.1.99", "200.1.1.1",
"www.microsoft.com", "www.hfkhkhfhkf.com" };
IPStatus _result;;
foreach (string _Host in HostAdrr)
{
Stopwatch timer = Stopwatch.StartNew();
_result = PingHostAddress(_Host, 1000);
timer.Stop();
Console.WriteLine("Host: {0} Elapsed time: {1}ms Result: {2}", _Host, timer.ElapsedMilliseconds, _result);
Console.WriteLine();
}
Console.ReadLine();
}
public static IPStatus PingHostAddress(string HostAddress, int timeout)
{
if (string.IsNullOrEmpty(HostAddress.Trim()))
return IPStatus.BadDestination;
byte[] buffer = new byte[32];
PingReply iReplay = null;
using (Ping iPing = new Ping())
{
try
{
//IPAddress _HostIPAddress = Dns.GetHostAddresses(HostAddress).First();
iReplay = iPing.Send(HostAddress,
timeout,
buffer,
new PingOptions(64, true));
}
catch (FormatException)
{
return IPStatus.BadDestination;
}
catch (NotSupportedException nsex)
{
throw nsex;
}
catch (PingException pex)
{
//Log/Manage pex
}
//catch (SocketException soex)
//{
//
//}
catch (Exception ex)
{
//Log/Manage ex
}
return (iReplay != null) ? iReplay.Status : IPStatus.BadDestination;
}
}
异步版本使用.SendPingAsync()方法并具有通常的异步签名。
public async Task<IPStatus> PingHostAddressAsync(string HostAddress, int timeout)
{
//(...)
iReplay = await iPing.SendPingAsync(HostAddress,
timeout,
buffer,
new PingOptions(64, false));
//(...)
}
使用异步版本时结果不会改变。使用 Winforms 测试。不管有多少人想弄乱 UI.
如何解读结果：
参数：
- 由 Ping.Send() 方法解析的主机名。 （预先解析主机名不会改变结果）
- 超时： 1000 毫秒（还测试了 500 毫秒和 2000 毫秒）
- 缓冲区： 标准 32 字节
- TTL: 64
- 不要分段： 正确
Host: 192.168.2.1 => Reachable Host in the same network.
Host: 192.168.2.201 => Unreachable (off) Host in a reachable different subnet.
Host: 192.168.1.99 => Non existent Host in a reachable different network (hardware routed)
Host: 200.1.1.1 => Non existent Internet Address
Host: www.microsoft.com => Reachable existing resolved Internet Host Name
Host: www.hfkhkhfhkf.com => Non existent unresolvable Internet Host Name
Host: 192.168.2.1 Elapsed time: 4 Result: Success
Host: 192.168.2.201 Elapsed time: 991 Result: TimedOut
Host: 192.168.1.99 Elapsed time: 993 Result: TimedOut
Host: 200.1.1.1 Elapsed time: 997 Result: TimedOut
Host: www.microsoft.com Elapsed time: 57 Result: Success
Host: www.hfkhkhfhkf.com Elapsed time: 72 Result: BadDestination
As also noted by @PaulF in the comments, the only (persistent) anomaly is the first response if the Host is unreachable: it's always a bit shorter than the imposed timeout. But the Timeout is always respected (the Ping method always returns within the set time interval).
Ping 到 8.8.8.8 这样的 IP 地址绝对没问题，但是当 ping 到像 www.google.com 这样的 dns 地址时，随机超时。
我认为这些随机超时与 dns 解析有关，与 ping 超时无关
private static bool DoPing()
{
try
{
using (System.Net.NetworkInformation.Ping ping = new Ping())
{
PingReply result = ping.Send("8.8.8.8", 500, new byte[32], new PingOptions { DontFragment = true, Ttl = 32 });
if (result.Status == IPStatus.Success)
return true;
return false;
}
}
catch
{
return false;
}
}