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# Record and replay on servers with SNI enabled

Server Name Indication (SNI) is an extension of the TLS protocol, in which a client indicates which hostname it is attempting to connect to at the start of the handshaking process. This allows multiple certificates to be sent from a single server. It is often used on cloud servers, such as AmazonCloud.

You can control whether VuGen sends an SNI extension to SSL handshakes using:

`web_set_sockets_option(“TLS_SNI”, <value>);`

Where:

Value | Description
--- | ---
"1" | Default. Enable extension and send the server name value derived from the URL (host name)
"0" | Disable extension. Do not send an SNI extension with SSL handshakes.
"<server name>" | Manually specify the SNI extension value for the next handshake only.

## Additional SNI guidelines

VuGen uses the following guidelines for SSL handshakes:

During recording:

- If SNI support is detected, no special step is added.
- If SNI is not detected, a
  `web_set_sockets_option(“TLS_SNI”, “0”);`
  statement is added to the beginning of the script.

During replay:

- When the `<server_name>` option is used, the specified server name is used for the next handshake only.
  Subsequent handshakes revert to the standard enabled (1) or disabled (0) behavior.

- If no `web_set_sockets_option(“TLS_SNI”, <value>);` statement exists, or if a `web_set_sockets_option(“TLS_SNI”, "1");` exists, the default SNI extension is sent with each SSL handshake.

  Therefore, scripts created prior to support of this option will run with SNI enabled.

  To prevent this behavior, add `web_set_sockets_option(“TLS_SNI”, “0”);` to your script.

https://admhelp.microfocus.com VuGen,Professional Performance Engineering,Performance Engineering for Developers 8942
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