Router DS/US Lights Blinking (Cable Modems)
DS and US lights blinking on your cable modem or router — what downstream and upstream channels mean, causes, and how to fix them.
Fast Blink
green
Visual description
On cable modems and modem-router combos (common with Xfinity, Spectrum, Cox), the front panel has individual LEDs labeled 'DS' (Downstream) and 'US' (Upstream), or sometimes 'Receive' and 'Send'. When actively blinking, the modem is in the process of scanning radio frequencies to lock onto your ISP's signal. Both LEDs blinking together is normal during startup. Only DS blinking (US not lit) means the modem is still in early channel scanning.
What it means
DS and US LEDs display the status of the coaxial cable connection between your modem and your ISP's local node. When blinking, the modem is actively searching for and locking onto signal channels. This is called 'channel bonding' — modern cable connections use multiple frequencies simultaneously for higher speeds.
During a normal startup, DS blinks first (finding downstream channels), then US blinks (uploading registration), and finally both should turn solid, indicating a full lock. Total time for this process is typically 30–90 seconds.
If DS or US stays blinking for more than 5 minutes without going solid, the modem cannot lock onto channels — which indicates a signal problem from your ISP, coax cable issue, or splitter problem.
Brand & model variations
The same light pattern can mean different things across manufacturers.
| Brand / Model | What green fast blink means | Recommended action |
|---|---|---|
Arris / Surfboard SB6183, SB8200 | DS = downstream channel lock. US = upstream channel lock. Both solid green = bonded and working. Blinking = still scanning. Solid blue on SB8200 = DOCSIS 3.1 active (best mode). | If both don't go solid within 3 minutes, check coax connection. |
Motorola MB7420, MB8600 | Same DS/US labeling as Arris. DS blinks first, then US. Both solid = online. Yellow DS = partial channel lock (degraded signal). | Yellow DS = call ISP for signal level check. |
Xfinity Gateway XB6, XB7 | Xfinity gateways don't label DS/US separately — they show an 'Online' or single status LED. The equivalent blinking phase is orange (connecting) → white/green (connected). | See 'router blinking orange' for Xfinity-specific guidance. |
Netgear CM600, CM1000 | DS and US labeled the same way. Downstream may show multiple lights (each light = a bonded channel). More lit downstream lights = more bonded channels = higher speeds. | If only 1–2 DS lights are lit when you had more before, signal degradation has occurred. |
Diagnose your issue
Answer a few questions to narrow down the cause.
How long have the DS/US lights been blinking?
Safe next steps
Ordered from least to most involved. Check each step as you go.
Wait 3 minutes from power-on before troubleshooting — channel scanning is normal.
Check that the coaxial cable (the thick cable with the threaded connector) is finger-tight at both the modem and the wall outlet.
Connect the modem directly to the wall coax outlet — bypass any splitters or amplifiers temporarily to test.
Access the modem's status page at 192.168.100.1 (most DOCSIS modems) to read downstream/upstream signal levels.
Reboot the modem (unplug 30 seconds), then wait 2 minutes.
Check your ISP's outage map for your address.
If signal levels are outside acceptable range, request a technician visit from your ISP — this is a line issue they must fix.
When it resolves on its own
Condition: During normal channel bonding on startup
Expected time: 30–90 seconds on a healthy line. Up to 3 minutes on a marginal signal.
When to escalate
Stop troubleshooting and contact your ISP or manufacturer if:
- DS/US blinking persists more than 5 minutes with coax directly connected to wall.
- Signal levels on the modem diagnostic page are outside -7 to +7 dBmV downstream or 38–48 dBmV upstream.
- T3/T4 timeout errors visible in modem event log — these indicate upstream ranging failures that require ISP intervention.
- Other homes in your area also have outages.