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Slow internet speeds on LAN connect devices on CGNM-3552

I plan to stick around

I connected a MacBook directly to the CGNM 3552 using a cat5e ethernet cable. The LAN port flashes Amber. I plugged out all other devices.


Running a speed test on the MacBook I get consistent speeds of 200 mbps. However, when I connected another device (for example, ChromeCast Ultra) via ethernet cable and run another speed test, the speed drops to 80 mbps. (Note, the ChromeCast is idle and not casting). I removed the ChromeCast connection and connected a Phillips Hue Hub via ethernet cable. I got the same speed result, around 80 mbps. With 3 devices plugged in, the speed test drops to around 35 mbps.


I did this test several times and connected various devices to the LAN ports. It appears that when 2 or more devices are connected via LAN, the internet speed on the LAN drops significantly, download only. Upload speed is always the same.


Also note, leaving 2 devices plugged in I unplugged the MacBook and connected via wifi. Running the speed test again on the MacBook I get 250 mbps. So it seems wifi connected devices are not affected by the number of devices plugged into the LAN.


I’ve been through all the available settings and can see anything that would be causing this. I was under the impression that LAN connect devices would be faster than wifi connected devices.


I'm also hoping someone else can also perform this simple test and post their findings.


Re: Slow internet speeds on LAN connect devices on CGNM-3552


Hello, @The_One.


I appreciate the troubleshooting you have done so far to isolate the root cause of the slow speeds you are experiencing on a wired connection. 


I'm assuming the CGNM-3552 modem is in gateway mode when connecting more than one device to the Ethernet ports. 


I believe you were using C80 in AP mode. Have you tried putting the modem in bridge mode and using your C80 in router mode? In this setup, you would connect any wired devices directly to the router (C80). 


Since not many in the Community may be using the CGNM-3552 modem, you may not get a response for the test you have asked for.


You can try doing a factory reset of the modem to see if this resolves the speed degradation of wired connections. 


Please keep us posted on the outcome of the modem reset. 



Re: Slow internet speeds on LAN connect devices on CGNM-3552

I plan to stick around
Thanks for replying. Correct, I am using the modem in Gateway mode and connecting devices to the Ethernet ports. The goal of adding the C80 was to have more LAN ports. .

Ultimately, as I’m paying monthly for this modem I’d like to know if it’s just a setup/setting or the modem is defective and should be replaced. As you can see trying to explain that I might have a defective modem has been difficult in this scenario.

I will try both a factory reset and bridge mode and post what I find. Although I thought I read that the LAN ports on CGNM are not usable in this mode which will leave me short LAN ports.

Re: Slow internet speeds on LAN connect devices on CGNM-3552

I plan to stick around

I performed a factory reset using the external button (previous resets was using the menu). The speed tests now show 120 mbps so there is an improvement, however not to the speeds expected.


Next I set the CGNM to Router mode. I connected 3 routers together as follows:


     CGNM(routing mode) -> cat5e -> TP-Link -> cat5e -> D-Link(access point)


I connected devices to all the LAN ports with on both the TP-Link and D-Link and the speed test shows +250mbps on both routers on all of the LAN ports. This setup works perfectly.


I can only conclude at this point the CGMN has an issue. It's an old device so I understand. I’m just not sure I will be able convince Rogers support of this issue in order to have it replaced.  

Re: Slow internet speeds on LAN connect devices on CGNM-3552

I've been around

Hi @The_One ,


I'm currently encountering a similar issues.

On my network, I have 3 Gigabit Network items and 1 Raspberry pi (only the pi have 10/100). All are connected with Cat5e cable.


After a factory reset, it does seem to fix the issue for a short period of time, but continue to monitor this for a few days. In my case, it was able to sustain 300mbps against for the first few hours, then afterwards, drop down to 10-20mbps in subsequent tests. Unplugging all devices, hard reboot, and testing individual devices give mixed results (sometime reaching 150-300mbps, then 10-20mbps on the same device). All wifi device are unaffected, only Ethernet connected items. All ethernet ports are Amber / flashing Amber (except for the pi; of course)


If this could help the Roger's Tech, the firmware I've is ""

Re: Slow internet speeds on LAN connect devices on CGNM-3552

I plan to stick around

Hi @ST_17,


Thank you for this information. (I feel a little better now that it's not just me as I've spent a number of weeks testing this.)


My experience was the same where immediately after the factory reset, the speeds were above 250+ and then degrades. Each time after factory reset it would degrade at a different pace. This behavior also suggests to me that modem is capable but has some issue. 


I also have firmware "" 

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