I've been using FreeTDS with 8.0 protocol for some time to connect to a MSSQL Database, and things have worked great. But, recently, things started to not work so great. I'll spare the details.
So we decided we needed to know a bit more, and I am a bit confused by the following:
Does FreeTDS support Microsoft servers?
Yes. Microsoft servers don't usually accept TDS 5.0 connections. Use one of versions 4.2, 7.0 or 8.0 of the protocol. See the User Guide for details.
[No mention of 8.0 anywhere on the page.]
So, what is TDS Protocol Version 8.0 and why should I use it?
FreeTDS "version 8" is actually version 7.1. Unfortunately, you have to look at the "history of TDS versions" page to figure that out, but here's the explanation from there:
Earlier FreeTDS documentation referred to versions 7, 8 and 9. Microsoft subsequently published a protocol specification document denoting 7.1 and 7.2, and one finds scattered references using that scheme elsewhere, too. For that reason, FreeTDS switched to Microsoft's nomenclature.
来源：https://stackoverflow.com/questions/10889294/what-is-tds-protocol-version-8-0-and-why-should-i-use-it