To enable auto speed duplex/negotiation both sides of the link have to have it enabled. If one end is configured for auto/auto and the other is not then the standard says the auto/auto end has to assume it is half duplex. So it is very common for a provider to configure a link 100/full - and if you leave your end auto/auto will will fall back to 100/half. So make sure you configure your end 100 full to [almost certainly] match what your provider has configured. Also note that SFPs don't usually support speed negotiation. However I am not sure in the case of this specific SFP - but I would not have high hopes. It is pretty rare to get routers with actual 100Mb/s ports these days. You could ask your provider if the port is Gigabit capable, and if so, could they change it to auto/auto. This would make your life much easier.
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