Setting up 5Gb on a 10Gb LAN is possible with proper configuration.
Setting up 5Gb on a 10Gb LAN is possible with proper configuration.
ATT has been deploying 2.5 and 5gb internet recently, and since I reside in Dallas, I’m able to access their 5Gb service. They supplied a BGW320-500 modem with a fiber connection and four RJ45 ports—three at 1Gb and one at 5Gb. Linking the 5Gb port directly to my motherboards’ 2.5Gb port lets me achieve full 2.5Gb upload and download. Rather than installing a subpar 5Gb card, I decided to upgrade my local network to 10Gb. I purchased several items: two SFP+ cables from "10Gtek", two Mellanox ConnectX-3 units (from eBay), one Ipolex RJ45 transceiver for the 5Gb link, and a CRS305-1G-4S+IN Mikrotik switch. After assembling everything, I performed a speed test. I can retrieve the full 5Gb download rate, though the upload remains very slow—under 1Gb. I questioned whether the switch or hardware was faulty, so I ran iperf between my NAS and desktop, which showed much higher performance. Connecting to host 192.168.1.79 on port 5201 (and other ports) demonstrated solid throughput across various intervals. The interface on the ATT modem shows a 5Gb connection, but the switch software indicates 10Gb. This suggests it isn’t properly negotiating the speed. It seems the transceiver might be the issue. I’ve ordered a MikroTik S+RJ10 to test further. This configuration could become more popular as users seek better 5Gb capabilities. Are there other factors affecting performance I should consider?
I experienced the same challenge with a 10G port and a mgig transceiver limiting my uploads. My configuration now routes the device through a switch supporting 1/2.5/5/10Gbps on select ports, then directs it to a separate VLAN for firewall access. The current path is: BGW320 5Gbps → Switch port (5Gbps) → Switch port (10Gbps) → Firewall. It would be wise to upgrade to a switch with 5Gbps capability or better and use it directly.
These RJ45 SFP+ devices function as a compact two-port switch since the SFP+ standard doesn’t actually support speeds between 1Gb and 10Gb. They connect to their host at 10Gb and to an external port via the RJ45 interface. The standard doesn’t provide any guidance for sharing this speed info or enabling RJ45 modules. When reviewing the module type listed by the device, it often appears as a DAC or fiber module. Mikrotik’s S+RJ10 model uses one unused pin pair to add metadata for the RJ45 link speed—a feature exclusive to Mikrotik. This approach may not be cost-effective now, but it could have been worth considering earlier. No other vendor has implemented this before. Their documentation notes “link speed reporting is fixed,” though in reality it wasn’t feasible within SFP+ constraints. They found a workaround that allows compatibility with other manufacturers’ gear. If you’re using a router, what device are you connecting to? You might try inserting the RJ45 module into one of your Connect X-3 cards and linking it to the modem or router for extra bandwidth.
It seems we're revisiting a previous discussion, though no new answer was given. To fix the upload speed problem, you should enable flow control on the switch.