if i understand correctly you want to test the link as per the delivery of MPLS
in industry test, we do iperf testing between site to site. - https://iperf.fr/iperf-doc.php
is this what you looking ?
You are right, my ISP send me a report with the bandwidth provided, but in many opportunities we have noticed that they have reduced the bandwidth that we have by contract, so I need a way to verify that offently. Is there any way?
the suggestion to use iperf is a good one.
However, to test bandwidth you should use UDP streams, because TCP throughput is influenced by the bandwidth delay product. If the two sites are geographically far TCP results will be lower then UDP ones even if the service provider is doing its best and it is conforming to contracted SLAs.
To be noted in some cases you can send multiple TCP sessions concurrently over the path and the aggregate throughput will be more close to single UDP session test results.
Hope to help
you need to install the iperf SW on two different PCs one located in site1 and one located in site2.
This is the way to use a tool like iperf.
One PC will act as client and the other will act as server and you can perform different tests based on TCP or UDP.
You can make multiple tests and you can exchange roles over time. To see also if there is any change in performance when changing the server role position.
This kind of tests are invasive and will have impact on normal user traffic so tests should be performed when users are not in office.
Hope to help
This what i have suggested on other post (use iperf), and suggest to do this test due to impact and clear outcome, suggest to do it in off peak business hours, so you have base line zero business traffic to test different methods.