The NETGEAR Nighthawk CAX80 has a long thread record on the NETGEAR community of owners on cable plans, such as Xfinity, who see speeds far below the plan, including 80 to 90 Mbps on the Ethernet ports on a gigabit-class line and slow Wi-Fi even next to the router, and the causes fall into the line, the ports and the settings. The first test is the same for all: connect a computer by Ethernet to the CAX80 and run a speed test at a quiet time, then compare it with the plan.
The checks in more detail
Because the CAX80 is a cable modem, its speed also depends on the cable signal levels, and a poor signal limits the speed, so open the CAX80's cable connection status page and look at the downstream power and signal-to-noise figures and any uncorrectable errors; high error counts mean a line problem for the provider to fix. Check that the cable connection and splitters are good, and that there is no unnecessary splitter between the wall and the modem. Then look at the ports and the cable.
A wired link that negotiates at 100 Mbps because of a bad cable gives the 80 to 90 Mbps figure that owners report, so replace the cable with a good Cat5e or Cat6 and try another port. Check that the QoS and traffic features are off in the advanced settings, since they can cap speed on a fast plan. For Wi-Fi, use the 5 GHz band for speed and place the router in the open, central and high. Give each band its own name so that devices join the 5 GHz band.
Update the firmware, and check whether the modem is on a version supported by the provider. Restart the CAX80, leaving it off for a minute, since a cable modem needs a full restart to renegotiate its channels with the provider. Test with the CAX80 on the plan's recommended tier, since a plan with a lower tier gives lower speeds. If wired speeds stay far below the plan with good cables, the signal levels fine and QoS off, the provider should check the line, or NETGEAR should check the unit.
Differential
Likely causes of “NETGEAR Nighthawk CAX80 cable modem router internet or Wi-Fi is slow”, and how to tell them apart
- 1
A poor cable signal
What separates it Low speeds and errors on the status page
How to confirm Ask the provider to fix the line
- 2
A cable negotiating at 100 Mbps
What separates it 80 to 90 Mbps wired
How to confirm Replace the Ethernet cable
- 3
QoS or traffic features on
What separates it A cap on a fast plan
How to confirm Turn them off
- 4
A device on 2.4 GHz
What separates it Slow Wi-Fi
How to confirm Name each band and join 5 GHz
- 5
A modem that needs a restart
What separates it Channels are poor
How to confirm Power cycle for a full minute
Before you touch a setting
Record this first — changing settings destroys the evidence
- The wired speed
- The cable signal levels and error counts
- The Ethernet link speed
- The plan tier
Try in this order
0 of 6 completedTest wired speed
ReversibleAt a quiet time.
Read the cable status page
ReversiblePower, SNR and errors.
Replace the Ethernet cable
ReversibleCat5e or Cat6.
Turn off QoS
ReversibleAnd traffic features.
Name each band
ReversibleJoin 5 GHz.
Power cycle the modem
ReversibleFor a minute.
Model-specific
What is true of this model and not of its siblings
- Cable modem
- Its speed depends on the line.
- 100 Mbps link
- A bad cable can cause it.
Stop boundary
When this stops being a self-service repair
- !If signal levels are poor, contact the provider
- !If wired speed stays low with good cables and levels, contact NETGEAR
- !Update the firmware
Evidence ledger
Sources behind this answer
CAX80 owners with speeds far below plan.
Owners seeing slow speeds on the CAX80's Ethernet ports.
NETGEAR's guide to double NAT with an ISP gateway.
Exact questions
Common questions
Why is my CAX80 slow?+
A line problem, a 100 Mbps link or QoS.
Why 80 to 90 Mbps on Ethernet?+
The link may have negotiated at 100 Mbps.
Where are the signal levels?+
In the cable connection status page.
Should I restart it?+
Yes, for a full minute.