Help! Netgear C7000-100NAS modem/router goes slow, speeds up when Ethernet cable is unplugged??

[Jonty13]

This new modem/router gave 56Mbps then suddenly slowed to 0.3Mbps on both Ethernet and WiFi. Had me tearing my hair out. Then when I unplugged the printer's Ethernet connection from the router, I saw out of the corner of my eye speedtest.net shot back up to 56Mbps (on a hard-wired computer).

A little later, the same thing happened with a Netgear AV200 Powerline Adapter - unplugging its cable sped up the router. Finally, a Netgear 5-port switch did the same thing.

It's been stable at 56Mbps for a couple of days now with one computer, couple of VoIP boxes and an Alarm System Gateway box plugged into Ethernet ports plus two tablets, two laptops and a Tivo connected wirelessly. I've never seen this behavior before, I thought Ethernet ports couldn't affect each other or affect the speed of the network (other than hogging bandwidth - but surely not from 56 to 0.3Mbps, especially when the printer wasn't printing and Powerline Adapter wasn't streaming??). Anybody got any ideas? Is this normal, or should it go back to BestBuy?

 

[schwatzz]

Try disabling QoS on the router. Try updating the router to the latest firmware.

 

[Jonty13]

Thank you schwatzz - it's a modem/router so Time Warner Cable handles firmware upgrades but so far as I can tell, the firmware is current. QoS - interesting, called VMM on this kit, I'll be trying that after I earn my crust today.

I looked at the Event log which showed this message 15 times "SYNC Timing Synchronization failure - Failed to acquire QAM/QPSK symbol timing;;CM-MAC=b0:7f:b9:6f:d5:28;CMTS-MAC=00:00:00:00:00:00;CM-QOS=1.0;CM-VER=3.0;", said it was "Critical (3)" - the timing seemed to correspond to the slowdowns, there've been no more messages and no more slowdowns.

Can you tell me what this means?

 

[Jonty13]

The problem occurs when the Netgear XAV200 Adapter is connected to the router. But I get Internet connectivity from the distant adapter when the adapter by the router is not connected. I must be picking up another powerline network nearby!! Why that would drop internet speed from 56 to 1Mbps on all connected devices is a mystery. I have changed the encryption keys on my adapters which made the other two adapters disappear from the powerline utility network map which is encouraging - now for a new test ...

 

[Jonty13]

New test shows 56/5Mbps with the Netgear XAV200 Adapters connected, up from 1/0.3Mbps. Through the Netgear ethernet extender adapters, I get 37/5Mbps, about right for AV200s, up from 1/1Mbps. Success! I guess the moral of this story is change the encryption key on ethernet extenders!