It's not a modem, it's direct ethernet connection into the provider's hardware, located outside of the appartment. And it's only 100Mbps. I would prefer the router to not even try 1Gbps for external link.Code:Link UP at 100 mbps full duplex
The vast majority of modern modems have a 1 Gbps interface. If it only rises at 100 Mbps then it usually indicate a faulty cable, causing the connection to fallback to 100 Mbps.