Client machines are failing in getting configuration or sending basic inventory.

The agent logs shows messages like these:

Policy request failed, COM error: An existing connection was forcibly closed by the remote host (0x80072746)

-OR-

Error type: Network error
Error code: An existing connection was forcibly closed by the remote host (10054)

While trying to reach the actual SMP server, we were able to ping but if we tried opening the Console, we got "page can't be displayed". If we used the actual IP Address it worked. We added the IP and name references into the Host file but it didn't help.
We noticed some type of delay when we were trying to reach the get configuration or post pages.
As well if we tried to reach the NSCAP or any other share on the SMP, we either saw a long delay to reach the destination or we had to use the IP address to reach out.

Message 1:

Policy request failed, COM error: An existing connection was forcibly closed by the remote host (0x80072746)
-----------------------------------------------------------------------------------------------------
Date: 11/9/2017 2:33:53 PM, Tick Count: 574619433 (6.15:36:59.4330000), Size: 341 B
Process: AeXNSAgent.exe (1052), Thread ID: 2988, Module: AeXNSAgent.exe
Priority: 1, Source: ConfigServer
 

Message 2:

Operation 'Direct: Post' failed.
Protocol: HTTPS
Host: mySMP.example.com:443
Path: /altiris/NS/Agent/GetClientPolicies.aspx
Id: 1818.1052
Error type: Network error
Error code: An existing connection was forcibly closed by the remote host (10054)
Error note: SocketIOStrategySyncSelect::Send error
Server HTTPS connection info:
Server certificate:
Serial number: 24 83 2c d9 99 e7 c3 b8 4a 85 ce e3 df 55 ea 58
Thumbprint: eb 5f 9e 7d dc 3f 71 08 8f f0 20 a5 fd e7 c6 13 28 4f 72 a3
Cryptographic protocol: TLS 1.0
Cipher suite: TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA_P256
Cipher algorithm: AES
Cipher key length: 256
Hash algorithm: SHA1
Hash length: 160
Key exchange algorithm: ECDH_P256
Key length: 256
-----------------------------------------------------------------------------------------------------
Date: 11/9/2017 2:33:53 PM, Tick Count: 574619433 (6.15:36:59.4330000), Size: 1022 B
Process: AeXNSAgent.exe (1052), Thread ID: 2988, Module: AeXNetComms.dll
Priority: 1, Source: NetworkOperation

Usual message from a Site Server:

Operation 'Direct: Head' failed. 
Protocol: HTTPS 
Host: mySMP.example.com:443
Path: /Altiris/TaskManagement/ClientTask/ExecTSMethod.aspx 
Connection Id: 220.8004 
Communication profile Id: {78AEE57F-7B55-4AEE-89A7-F619DFE99CEB} 
Throttling: 0 0 0 
Error type: Network error 
Error code: An existing connection was forcibly closed by the remote host (10054) 
Error note: SocketIOStrategySyncSelect::Send error
-----------------------------------------------------------------------------------------------------
Date: 10/11/2021 8:19:08 AM, Tick Count: 134945125 (1.13:29:05.1250000), Size: 661 B
Process: AtrsHost.exe (8004), Thread ID: 3112, Module: AeXNetComms.dll
Priority: 1, Source: NetworkOperation 

Web request 'POST' failed: https://mySMP.example.com:443/Altiris/TaskManagement/ClientTask/ExecTSMethod.aspx?clientTaskServerGuid=e60b4be4-bf54-43eb-be17-a94cc70c7a89.
   [Altiris.DotNetLib.Interop.AeXNetComms.Web.Exceptions.AeXWebRequestException @ Altiris.DotNetLib]
   at Altiris.DotNetLib.Interop.AeXNetComms.Web.AeXWebRequest.Execute(String requestUriString, Guid cnnProfileId, TimeSpan timeout, Boolean isPost, String data)
   at Altiris.DotNetLib.Helpers.AtrsHttpOps.Execute(String url, Guid cnnProfileId, TimeSpan timeout, Boolean isPost, String data)
   at Altiris.ClientTask.Server.Communication.NotificationServerWebConnection.PostToNotificationServerWithRetry(String url, Guid cnnProfileId, String data, Int32 nMaxAttempts, TimeSpan timeout)

One or more errors occurred.
   [System.AggregateException @ mscorlib]
   at System.Threading.Tasks.Task`1.GetResultCore(Boolean waitCompletionNotification)
   at Altiris.DotNetLib.Interop.AeXNetComms.AeXAsyncRequest.Execute()
   at Altiris.DotNetLib.Interop.AeXNetComms.Web.AeXWebRequest.Execute(String requestUriString, Guid cnnProfileId, TimeSpan timeout, Boolean isPost, String data)

Web request 'POST' failed: https://mySMP.example.com:443/Altiris/TaskManagement/ClientTask/ExecTSMethod.aspx?clientTaskServerGuid=e60b4be4-bf54-43eb-be17-a94cc70c7a89.
   [Altiris.DotNetLib.Interop.AeXNetComms.Web.Exceptions.AeXWebRequestException @ Altiris.DotNetLib]
   at Altiris.DotNetLib.Interop.AeXNetComms.Web.AeXWebRequest.OperationCallback(IAeXNetworkTransport5 transport)
   at Altiris.DotNetLib.Interop.AeXNetComms.AeXRequest.ExecuteRequestSyncCallbackImpl(IAeXNetworkTransport5 transport)
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at Altiris.DotNetLib.Interop.AeXNetComms.AeXAsyncRequest.<ExecuteCallback>d__56.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at Altiris.DotNetLib.Interop.AeXNetComms.AeXTransportInstance.<ExecuteRequestCallback>d__13.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at Altiris.DotNetLib.Interop.AeXNetComms.AeXPooledTransportInstance.<ExecuteRequestCallback>d__8.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at Altiris.DotNetLib.Interop.AeXNetComms.AeXTransportManager.<ExecuteRequest>d__44.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at Altiris.DotNetLib.Interop.AeXNetComms.AeXAsyncRequest.<ExecuteAsync>d__55.MoveNext()

An existing connection was forcibly closed by the remote host
   [System.Runtime.InteropServices.COMException @ Altiris.AeXNetwork.Transport.1]
   at Interop.AeXNetComms.AeXNetworkTransportClass.IAeXNetworkTransport5_Post(String url, String data, Int32 decompress)
   at Altiris.DotNetLib.Interop.AeXNetComms.Web.AeXWebRequest.OperationCallback(IAeXNetworkTransport5 transport)

COM Exception errcode: 0x80072746

Exception logged from: 
   at Altiris.DotNetLib.Logging.AtrsLog.ExceptionMessage(String message, Exception exception)
   at Altiris.ClientTask.Server.Logging.NSAgentLog.ReportMessage(Severity severity, String moduleName, String source, Exception exception, String message, Object[] arguments)
   at Altiris.ClientTask.Server.Communication.NotificationServerWebConnection.PostToNotificationServerWithRetry(String url, Guid cnnProfileId, String data, Int32 nMaxAttempts, TimeSpan timeout)
   at Altiris.ClientTask.Server.Communication.NotificationServerWebConnection.PostToNotificationServer(String url, Guid cnnProfileId, String postData, String& respData, Boolean& dataEncryped, Int32 nMaxAttempts, TimeSpan timeout)
   at Altiris.ClientTask.Server.Communication.NotificationServerWebConnection.ExecuteMethodOnNs(String methodName, String xmlParameters)
   at Altiris.ClientTask.Server.ClientTaskServer.RegisterClient(AltirisResourceGuid resourceGuid, IPAddress ipAddress, Boolean bLastResort, Boolean bBeingActive, String configurationXml, String crc, Hashtable& output, IAuthAgentConnection wsConnection, Version version, Nullable`1 resTypeGuid, String systemType)
   at Altiris.ClientTask.Server.ClientTaskServer.ProcessRemoteRegisterClient(Hashtable input, Hashtable& output)
   at Altiris.ClientTask.Server.HttpHandlers.WebClientApiManager.ExecuteService(String serviceName, Hashtable input, IAuthAgentConnection wsConnection)
   at Altiris.ClientTask.Server.HttpHandlers.WebClientApiManager.ProcessRegister(XmlTextWriter wr, NameValueCollection queryValues, Stream requestStream, Int32 contentLength, String address, IAuthAgentConnection wsConnection)
   at Altiris.ClientTask.Server.AgentActionHandlers.Register.HandleImpl(IAuthAgentConnection wsConnection, IAgentAction`1 action, XmlTextWriter wr, ResponseState state)
   at Altiris.TaskManagement.Common.ClientTask.AgentActionHandlers.TSAgentActionHandler`1.GetHandlerResponse(IAuthAgentConnection connection, IAgentAction`1 action, ResponseState state)
   at Altiris.TaskManagement.Common.ClientTask.AgentActionHandlers.TSAgentActionHandler`1.Handle(IAuthAgentConnection connection, IAgentAction`1 action)
   at Symantec.AgentActions.Handlers.AgentActionHandler`2.<Handle>d__5.MoveNext()
   at System.Runtime.CompilerServices.AsyncTaskMethodBuilder.Start[TStateMachine](TStateMachine& stateMachine)
   at Symantec.AgentActions.Handlers.AgentActionHandler`2.Handle(IAgentConnection connection, IAgentAction action)
   at Symantec.AgentActions.Connections.AgentConnection.HandleAction(IAgentAction action)
   at System.Threading.Tasks.Task`1.InnerInvoke()
   at System.Threading.Tasks.Task.Execute()
   at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
   at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
   at System.Threading.Tasks.Task.ExecuteWithThreadLocal(Task& currentTaskSlot)
   at System.Threading.Tasks.Task.ExecuteEntry(Boolean bPreventDoubleExecution)
   at System.Threading.ThreadPoolWorkQueue.Dispatch()

-----------------------------------------------------------------------------------------------------
Date: 10/11/2021 8:19:08 AM, Tick Count: 134945109 (1.13:29:05.1090000), Size: 7.12 KB
Process: AtrsHost.exe (8004), Thread ID: 8292, Module: AtrsHost.exe
Priority: 1, Source: NotificationServerWebConnection

ITMS 8.1 and later

There was a network configuration issue. Apparently, SMB traffic was not being passed properly.  Their MTU size was modified from its default value of 1500. They increased it to 9000 and it caused the issue. We changed back from 9000 to 1500 on the servers at that site.