Bell

Hi, with a 10 gig sfp in my switch connected with a cat8 cable to the 10 gig port on the modem did the trick. I don't have speed problem at all now.

Thank you will try that, and will let you know the results 

i already have a cat8 network cable, what i need is to buy a 10g copper gbic and try if it is better.

the speed is "ok" when using 1g port on the modem, but the deal is to be able to take advantage of my 1.5 g internet acces and not only 1g out of 1.5. i buy my 2.5g network sw for that purpose

Actually it is a 2.5 gig switch. When using the 2.5/5/10gig port on the modem directly connect to the switch, i see that the negociated speed  ont the switch is 2.5.g. There is nos error on the interfaces. I event try to manually set the speed on bot...