RT-AC88U ports 5-8 behaviour

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New Around Here
RT-AC88U running latest Asus firmware.

Hi - has anyone actually managed to figure out how the "2nd switch" in this router is supposed to work?

I have connected:
1.TP-Link powerline adapter - to 3 adapters in the house > LG TV, IP Cam, PS4.
2. Sky Q
3. LG TV
4. 5-port Netgear switch > Xbox One X, PS4, LG TV
5. Empty
6. Empty
7. 8-port Procurve switch > 3 x PC, printer, NAS, HPE Server (Windows)
8. Empty

It seems like nothing else is capable of working in ports 5/6/8. Powering off makes no difference. the Asus status shows:
1. Unplugged (no idea why it shows the PL adapter as unplugged, it always has)
2. 100Mbps
3. 100Mbps
4. 1Gbps
5. Unplugged
6. Unplugged
7. 1Gbps
8. Unplugged

I can move the Procurve switch between 5/6/7/8 without issues and the "other 3" then don't work if I connect something directly to them. Is this by design? If so it's nothing more than a 5-port switch on the router for me.

Also strangely, if I hook a PC up to the 2nd port on the powerline adapter it works fine until I try to move large amounts of data, then the whole router just packs in and no traffic gets onto the internet, yet internal traffic between other devices works. So odd.

I know there are more tests I could do with moving devices about, the problem is with us being in lockdown I'd need to be up in the middle of the night to get some actual downtime to test this further without the wife/kids screaming at me.

My thoughts are that when I buy an 8-port switch/router, I should be able to hang 8 switches off it if I should so please. Maybe if I put the powerline, Netgear and Procurve switches on ports 1-3 the ports on 5-8 would work better with individual devices. I have everything wired on static IP's so would not worry about the issue others have with DHCP on these ports.

Is there any "known" behaviour of this mystery 2nd switch in my router that I need to be aware of? Also I am new to forum posting and have no clue why my font changed half-way through this post.
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Occasional Visitor
What is known is that with the 88U the first four ports are controlled by the main microprocessor, while ports 5-8 are controlled by a sub-processor. There have been a number of "wierd" cases where ports 5-8 stop working. Usually unplugging the router (not just rebooting, must be unplugged) fixes the problem.
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Occasional Visitor
It's not been a big enough of an issue for me to complain about it. I noticed there was one problematic device, and once I moved that device to LAN ports 1-4, my 88 has worked great ever since. I know that's probably not the answer you're looking for; in an ideal world ports 5-8 would work as well as 1-4 and the router shouldn't care. But in my case after I swapped the devices around it's worked fine.


Occasional Visitor
Same here, I had 6 devices connected. Swapping them solved the problem for me. I already knew from reading the forums when I bought the thing that the latter 4 ports were controlled by a seperate processor, so I moved what I thought were the 4 most active devices to the first 4 ports. But the device I had connected to port 6 always seemed to be the trouble maker; I swapped that one and haven't had any problems since. But I can only speak to my own experience.


New Around Here
From my experience, it’s completely unpredictable I’m afraid. Some FW versions it was running better than others, but regardless of partial success, there ware always disconnection problems sooner or later. Almost guaranteed after reboot or power cut. I’ve tried different ports, different devices downstream, various “keep alive” methods, nothing helped.

The only permanent and fail safe solution is to plug a good switch in any of ports 1-4 and run as many other devices off that one instead. Consider 5-8 as “not installed”.

Probably not what you want to hear, but I’ve tried a lot of stuff, spent lot of hours and to no avail.

Some reasonably good managed Netgear switches are running pretty cheap on Black Friday Amazon and you can play some neat tricks with those as well, unless the dumb switch is all you need.

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