CM1000 Rock Solid at 500MBps until I upgraded Cox to 1000GBps

[NavyNate95]

I've used this modem for many years at speeds between 200-750MBps without issue. At my current location I've been using it at 500MBps without issue for 7 months. Then yesterday I upgraded to 1000MBps and I immediately started having internet dropouts for 5-10 minutes at a time every 2-4 hours, which has now been going on for 2 days. Cox is trying to tell me it's my modem, but I don't see how that could be considering it's been rock solid for so many years. 

Logs and status attached.

[FURRYe38 · Accepted solution]

Find you a -6db coax line attenuator to put in line between the modem and ISP coax line. 

FYI, the modem doesn't output any power, only recieves what the ISP is putting over the coax line. 

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@NavyNate95 wrote:

Tech just left. He said there was very low signal loss (around -47dbm) up to the modem and that Cox has no ability to change the power output of the modem. They reprovisioned the modem, but it still has high power levels of 8.5-11dBmV. The tech doesn't know what else to do except get a different modem. I don't really want to do that, so I'll let it ride and if it drops out any more I'm going to go back to 500MBps where it had been rock solid for 7 months.

The LAN cable between the eero and the modem is a Cat 8, and it's the same as it has been for months, so I don't think that's it, either.

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[FURRYe38]

Power levels are too high:

https://kb.netgear.com/24311/Power-level-guidelines-for-a-NETGEAR-cable-modem-router

Any Criticals, Errors or Warnings seen in the event logs needs to be reviewed and resolved by the ISP. Indicates a signal issue on the ISP line up to the modem.
Be sure your using a good quality LAN cable between the modem and router. CAT6 is recommended. 

Have the ISP check the signal and line quality UP to the modem. Be sure the ISP provisions the modem correctly.
Be sure there are no coax cable line splitters in the between the modem and ISP service box. 
Be sure your using good quality RG6 coax cable up to the modem. 
Start with removing any amplifiers, signal attenuators, or splitters from the coax.
From there check the line for kinks, damage, moisture in the line.
Check the connectors for improperly made ends, foil touching the copper coax line, loose connections, bad/old/cheap connectors, or corroded connections. Replace them if you do.
Be sure to power OFF the modem for 1 minute then back ON.
https://community.netgear.com/t5/Cable-Modems-Routers/General-info-and-Troubleshooting-for-Cable-Mod...
https://kb.netgear.com/24311/Power-level-guidelines-for-a-NETGEAR-cable-modem-router
https://www.duckware.com/tech/solving-intermittent-cable-modem-issues.html
https://highspeed.tips/docsis-events/

[NavyNate95]

Tech just left. He said there was very low signal loss (around -47dbm) up to the modem and that Cox has no ability to change the power output of the modem. They reprovisioned the modem, but it still has high power levels of 8.5-11dBmV. The tech doesn't know what else to do except get a different modem. I don't really want to do that, so I'll let it ride and if it drops out any more I'm going to go back to 500MBps where it had been rock solid for 7 months.

The LAN cable between the eero and the modem is a Cat 8, and it's the same as it has been for months, so I don't think that's it, either.

[FURRYe38 · Accepted solution]

Find you a -6db coax line attenuator to put in line between the modem and ISP coax line. 

FYI, the modem doesn't output any power, only recieves what the ISP is putting over the coax line. 

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@NavyNate95 wrote:

Tech just left. He said there was very low signal loss (around -47dbm) up to the modem and that Cox has no ability to change the power output of the modem. They reprovisioned the modem, but it still has high power levels of 8.5-11dBmV. The tech doesn't know what else to do except get a different modem. I don't really want to do that, so I'll let it ride and if it drops out any more I'm going to go back to 500MBps where it had been rock solid for 7 months.

The LAN cable between the eero and the modem is a Cat 8, and it's the same as it has been for months, so I don't think that's it, either.

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[NavyNate95]

Thank you, Furry! I can't believe I didn't think of that. Much appreciated!

[FURRYe38]

Also be sure to speed test with a wired PC connected directly to the back of the modem as well. Help rule out any performance issues with the external wifi router. 

[NavyNate95]

On the Cox supported modems site, the CM3000 is listed as having the identical 32x8 channel bonding and 1GBps speeds as my current CM1000. I don't see why I would spend hundreds of dollars on what is essentially the same modem I already have. 

Fortunately, I called Cox to downgrade back to the 500MBps that had been working without a single dropout for 7 months, and they gave me a Cox Panoramic Gateway router for free for two years so that I didn't downgrade. I'm going to pick that up this morning and put into Bridge Mode so it'll work with my eeros.