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iisnetwork-programmingtcpwindows-server-2016

TCP/IP connection time high when clients connect for the first time or reconnect after 3 minutes

I have a .NET MVC web application running on Windows Server 2016, IIS.

When I connect to the application it take over 20 seconds to establish the TCP/IP connection. All subsequent requests are fast. If I wait for about 3 minutes and try again, the problem reappears, same if I try to connect using a new anonymous window, or a different browser. If I connect to the application locally using a browser on the server it works fine. Based on Windows logs, the application pool isn't getting recycled. I tried turning off Windows Firewall temporarily with no luck.

Any idea what I should try?

Fiddler Statistics tab:

Request Count:   1
Bytes Sent:      227        (headers:227; body:0)
Bytes Received:  107        (headers:107; body:0)

ACTUAL PERFORMANCE
--------------
ClientConnected:    11:27:15.867
ClientBeginRequest: 11:27:15.868
GotRequestHeaders:  11:27:15.868
ClientDoneRequest:  11:27:15.868
Determine Gateway:  0ms
DNS Lookup:         0ms
TCP/IP Connect: 21013ms
HTTPS Handshake:    36ms
ServerConnected:    11:27:36.883
FiddlerBeginRequest:    11:27:36.883
ServerGotRequest:   11:27:36.883
ServerBeginResponse:    00:00:00.000
GotResponseHeaders: 00:00:00.000
ServerDoneResponse: 00:00:00.000
ClientBeginResponse:    11:27:36.883
ClientDoneResponse: 11:27:36.883

    Overall Elapsed:    0:00:21.014

Chrome devtools timing

Chrome devtools timing

Solution

  • Solved with some external help.

    This had nothing to do with the server, or the app. The issue was a duplicate DNS A record pointing to a server that is no longer operational.

    The client tried to connect there, timed out after 20 seconds and then retried with the second correct record. Then I assume the connection was kept open for a few minutes as long as there was activity so the subsequent pages loaded fine.