tcp window and SMB v3 multi session

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Hello Codec

Windows usually starts the 3-way handshake by offering a scale factor of 8. So you have to multiply the windows advertised by the client by 2^8 (in other words: multiply by 256).

A useful command could be netsh int tcp show global You could replace showwith set to change the various options. By default Windows is using a reasonably tuned network stack. Certain situations, like a connection with very high bandwidth and very long RTT, might require some fine tuning.

Windows supports a feature called "TCP offloading" which is sometimes called the "TCP chimney". With offloading enabled the network interface will do some work like calculating IP and TCP checksums. Another noteworthy feature to fine tune network performance is found within the hardware properties of your network card. Go to the properties of the network card. But instead of changing an IP address click the button "Configure...". In the new window locate the Advanced tab.

Especially on the server side you will benefit from a fine tuning of receive and transmit buffers provided by the NIC. You might want to try changing the maximum number of RSS queues.

One way to check the overall situation (preferably on the server) is the command netstat -es. You want to keep the number of discards, errors, retransmissions etc. as low as possible.

Please remember that Wireshark offers a great feature with the server response time statistics. Use the menu Statistics --> Service Response Time --> SMB2. In most cases the values for "Notify" will not deliver insight into the server performance, while all the others are great indicators.

Good luck!

Eddi