All ports should be usable. Ports 1 and 2 are WAN/Internet-facing RJ45 copper ports. Ports 3-10 are LAN-facing copper ports and Ports 11/12 are LAN-facing SFP ports. Ports 9/11 and 10/12 should not be "combo" ports, so using port 10 doesn't lock out port 12 or vice-versa. So you basically have all 10 LAN interfaces to use, the last 2 happen to be SFP instead of RJ45. I just did a quick lab test on an MX84 to prove it to myself, running 2 different VLANs/subnets on ports 9 and 11 at the same time, no issues. Hope that helps!