Ubiquiti's LED article gives the fastest Ethernet check: on ports other than the console, the Speed/Link/Act LED is green for a link at 1000 Mbps and amber for 10 or 100 Mbps, flashing for activity. An amber port on a gigabit device means a slow cable, a bad pair or a slow far end. Replace the cable first, since damaged cables are among the most common faults in Ubiquiti's offline article, then try a different port.
The checks in more detail
If you use SFP+ or multi-gig ports, check that modules and cables match the speed you expect and that the far device supports it. On the gateway, watch out for a link that negotiated 100 Mbps after a cable was disturbed and did not renegotiate; unplug and replug it. Check for a network loop, which Ubiquiti lists in its connectivity article and which makes wired traffic slow or fail. Look at switch port tagging and network overrides if a device gets the wrong address or none.
A speed test cabled straight to the gateway separates the gateway from the rest of the wired path. If one device is slow but the port is green, test the device with another cable, and check the device's own adapter. Update the application and devices, and if the port stays amber with a good cable, the port may be damaged, so use another and consider an RMA. Label your cables and keep a simple port map.
When a link is slow, the first question is which cable and which ports are involved, and a map turns a search through a rack into a two-minute check. Test a suspect cable with a laptop set to gigabit, and replace patch cables that have been kinked or pulled tight, since a damaged pair often falls back to 100 Mbps quietly. If the slow link is the WAN, test with a short patch cable between the modem and the gateway, since a long, old cable is a frequent cause of a link that will not reach its rated speed.
Differential
Likely causes of “Ubiquiti UniFi gateways Ethernet link is limited to 100 Mbps or disconnects”, and how to tell them apart
- 1
A bad cable
What separates it The port light is amber because the cable is bad
How to confirm Replace the cable, and then check whether the port light turns green
- 2
A slow far end
What separates it The link negotiated 100 Mbps because the device at the far end is slow
How to confirm Check the other device, and its network adapter, for the speed that it supports
- 3
A network loop
What separates it The wired traffic is slow or failing because there is a network loop
How to confirm Remove the loop, by unplugging the cable that connects the switches in a circle
- 4
Wrong VLAN tagging
What separates it The device gets the wrong address, or none, because of wrong VLAN tagging
How to confirm Fix the port tagging in the Network application, so the device is on the right network
- 5
A damaged port
What separates it The port light is amber even with a good cable because the port is damaged
How to confirm Use another port, and send the unit for an RMA if the port stays bad
Before you touch a setting
Record this first — changing settings destroys the evidence
- The color of the port light on the gateway
- The type of cable and of any module that is in use
- The speed that you measure at the gateway itself
- Whether a loop in the cabling is possible
Try in this order
0 of 7 completedRead the port LED
ReversibleRead the port light, since green means a link at 1000 Mbps and amber means 10 or 100 Mbps.
Replace the cable
ReversibleReplace the cable first, since a bad cable is the most common cause of a slow link.
Try another port
ReversibleTry another port, to rule out damage to the port that you were using at first.
Replug
ReversibleReplug the cable at both ends, so that the two devices negotiate the link speed again.
Check for loops
ReversibleCheck for loops, by unplugging the cables that might connect the switches in a circle.
Check VLAN tagging
ReversibleCheck the VLAN tagging, and any network overrides, on the port that the device uses.
Test wired at the gateway
ReversibleTest wired at the gateway, by plugging a laptop straight into it, to see the true speed.
Model-specific
What is true of this model and not of its siblings
- SFP+
- The Dream Machine Pro and SE have SFP+ ports; check techspecs.ui.com.
- Cloud Gateway Ultra
- The Cloud Gateway Ultra uses gigabit ports.
Stop boundary
When this stops being a self-service repair
- !If a known-good cable and port stay amber, RMA under warranty
- !If a loop is suspected, disconnect suspect cables
- !If one device is slow, check its adapter
Evidence ledger
Sources behind this answer
White, blue and port LEDs.
Cables, ports and RMA.
LED states, IP address checks and TCP 8080.
Wireless speed tuning.
The company and its products.
Exact questions
Common questions
What does green mean on a port?+
A green port light means a link at 1000 Mbps, which is gigabit speed.
What does flashing mean?+
A flashing port light means that there is link activity, so traffic is passing.
What is a loop?+
A loop is cabling that forms a circle, and it can disrupt all of the traffic.
Can VLAN tagging matter?+
Yes, VLAN tagging can matter, since it can leave a device with the wrong address.
Can a cable cause 100 Mbps?+
Yes, a cable can cause a link at 100 Mbps, particularly an old or damaged one.
What are SFP+ ports for?+
The SFP+ ports are for faster links, using modules that fit into the ports.
Should I RMA?+
Send it for an RMA if a good cable and port stay slow after all of the checks.