@ZHUO CHEN

Just an update for you...I did finally track down and fix my issues which were the same as yours. As suspected, there were several non-MoCA splitters in the network. Once I replaced all of them, including the main splitter at the entry-drop, my speeds are up to the 3.4 to 3.5Gbs (PHY) rate. I do have one MoCA adapter that is still hanging around 2.4 to 2.7Gbs (PHY) rate but that adapter is the furthest location in the house. A MoCA amplifier would most likely fix this slightly lower speed, but I don't feel that it's worth the cost to me. Best of luck on your journey!

Yuan, if the splitter is behind the wall do you know exactly where it is? Walls are pretty easy to repair especially if they are made of Sheetrock. I have kids so I have to fix holes in my walls all the time :)

There are so many possible variable for why you are seeing low link speeds. Some of the things to check for are: 1. Excessive number of splitters 2. Using non-MoCA compatible splitters 3. Poor cable connections (e.g. cables not fully tightened) 4. Interference from your cable/internet provider 5. Excessive line loss for a number of reasons (too many outlets on the extension, poor splicing, etc. Tracking down the reason for the poor link speed can be time consuming, but will pay off when you get everything to work correctly. I am actually going through this same issue as well. I have 4 MoCA 2500Ds and 2 of them have poor link rates. I am currently replacing all of the splitters with MoCA compatible splitters, placing resistors on all non-utilized outlets and splitter ends, and checking the cables as well as possible. Fun times....

If, however, the Fiber switch is managed by the ISP, you will need to place either a L2 switch or a router after that fiber switch and before the first MOCA device. You would then use that internal L2 switch or router to assign the external static IP address and to then assign DHCP address to your internal network. Lastly, the 1st MOCA device as shown in your wiring diagram, should either go before the fiber switch (if it's YOUR switch, not the ISPs) or, AFTER the Fiber Switch (it it's the ISPs fiber switch) but BEFORE your L2 Switch or Router. Upload a new/updated wiring diagram if you are still unsure and I will look it over ~Old IT Guy (as in older than dirt...)

Is the fiber switch yours or your ISPs? Assuming it's yours, you should assign the static IP to that switch then use DHCP for your internal network. You can, optionally, also assign static IPs to your GoCoax MOCA devices for easier management (which is what I do) but it's not strictly necessary.