You have a Gigabit network.

Your broadband connection might be 500 Mbps, 900 Mbps or faster.

Other computers get excellent speeds.

But one Windows 11 PC seems unable to get much beyond:

90–95 Mbps

Before blaming Windows, your ISP or the network driver, check something much simpler:

What speed has the Ethernet connection actually negotiated at?

If Windows reports:

100/100 Mbps

rather than:

1000/1000 Mbps

the problem is usually between your computer and the next Ethernet device.

And one of the most common causes is simply:

the cable.

Intel's own troubleshooting guidance says that when a Gigabit-capable adapter is correctly configured for Auto Negotiation but links at only 100 Mbps, the Ethernet cable is one of the first things to investigate.

Link Speed Is Not the Same as Internet Speed

This distinction is important.

Your Ethernet link speed is the connection between your PC and the next network device.

That might be:

PC → router

or:

PC → switch

or even:

PC → dock → wall socket → patch panel → switch

Your internet connection comes after that.

For example:

1 Gbps Ethernet + 80 Mbps broadband

means the local connection is capable of Gigabit speeds, but the internet service is the bottleneck.

Conversely:

100 Mbps Ethernet + 900 Mbps broadband

means the computer cannot make full use of the broadband service because its local Ethernet connection is already restricted to 100 Mbps.

That is why a speed test consistently topping out around 90–95 Mbps is such a useful clue.

Check Your Ethernet Link Speed in Windows 11

Open:

Settings > Network & internet > Ethernet

Look for:

Link speed

You might see:

100/100 Mbps

or:

1000/1000 Mbps

You can also press:

Windows + R

and enter:

ncpa.cpl

Double-click the Ethernet connection and check:

Speed

If it says:

100.0 Mbps

you have found an important part of the problem.

Your PC isn't merely getting a 100 Mbps internet speed test.

The Ethernet connection itself has negotiated at 100 Mbps.

Why a Damaged Cable Can Still Work

This catches people out constantly.

They assume:

“The cable can't be faulty because I still have internet.”

Unfortunately, it can.

Gigabit Ethernet over normal copper cabling uses all four twisted pairs.

100 Mbps Ethernet can operate using fewer pairs.

That means a cable can have a damaged conductor or bad termination and still provide a perfectly usable network connection—just at 100 Mbps instead of 1 Gbps.

That produces exactly the sort of fault where:

• internet works
• Outlook works
• Teams works
• websites load

but everything seems strangely capped around 90–95 Mbps.

Step 1: Replace the Cable

This should be your first test.

Not:

• reinstall Windows
• reset TCP/IP
• change Registry settings
• disable power management
• update the BIOS

Take a known-good Ethernet cable that you know has achieved Gigabit speeds elsewhere and connect it directly.

Then check the Windows link speed again.

If it immediately changes from:

100 Mbps

to:

1.0 Gbps

you've found the problem.

Intel similarly recommends reseating the Ethernet connection and testing another known-good cable early in the diagnostic process.

Do You Need Cat 6 for Gigabit?

No.

A properly manufactured and installed:

Cat 5e

cable is suitable for standard 1000BASE-T Gigabit Ethernet.

Cat 6 is also an excellent choice and gives additional performance headroom.

For a typical office:

Cat 5e → Gigabit capable

Cat 6 → Gigabit and useful headroom for faster networking

Cat 6A → commonly used where 10 Gigabit capability is required over full structured-cabling distances

Do not assume:

Cat 6 printed on cable = cable definitely good.

A damaged or badly terminated Cat 6 cable can still fail to negotiate Gigabit.

The quality of the complete connection matters.

Step 2: Try Another Switch or Router Port

If changing the cable makes no difference, move it to another known Gigabit-capable port.

A switch/router port can be:

• damaged
• manually configured to 100 Mbps
• physically worn
• limited to Fast Ethernet

Older routers and switches can also contain 100 Mbps interfaces.

Check the actual specifications.

If:

Port 1 = 100 Mbps

but:

Port 2 = 1 Gbps

you don't have a Windows problem.

You have a port limitation.

Step 3: Remove Everything Between the PC and Router

Office Ethernet rarely consists of one cable.

The actual route may be:

Laptop → dock → patch lead → wall socket → structured cabling → patch panel → patch lead → switch

Every part has to work correctly.

Temporarily simplify it.

Connect the computer directly to a known Gigabit switch/router port with a known-good short cable.

Then check Windows.

Now shows 1.0 Gbps

The PC is probably fine.

The fault lies somewhere in the original path.

Reconnect components one at a time.

Still shows 100 Mbps

Continue troubleshooting the PC, adapter and switch/router.

This process is much faster than changing ten settings simultaneously.

Step 4: Check the Wall Socket

Structured cabling faults are surprisingly common.

A wall socket may work at 100 Mbps but fail at Gigabit because of:

• poor termination
• damaged conductor
• incorrectly punched pair
• bad patch-panel termination
• damaged patch lead

If a direct cable to the switch gives:

1 Gbps

but the normal wall connection gives:

100 Mbps

you have narrowed the problem substantially.

Test:

patch lead → wall outlet → structured cable → patch panel → switch lead

rather than blaming Windows.

Step 5: Check the Dock

Laptop docking stations deserve particular suspicion.

Test:

Laptop through dock

then:

Laptop directly through built-in Ethernet or known-good USB Ethernet adapter

If the dock negotiates at 100 Mbps but the direct adapter achieves 1 Gbps, investigate:

• dock firmware
• dock driver
• Ethernet socket
• dock specification

Some older docks genuinely contain only 100 Mbps Ethernet.

Step 6: Check the Ethernet Adapter

Make sure the adapter actually supports Gigabit Ethernet.

Open:

Device Manager > Network adapters

Identify the wired adapter.

Look up its official specification.

Terms such as:

Gigabit Ethernet

GbE

10/100/1000

1GbE

2.5GbE

indicate support above 100 Mbps.

An adapter described as:

10/100

or:

Fast Ethernet

cannot negotiate at 1 Gbps because the hardware simply doesn't support it.

Be Careful With USB Ethernet Adapters

A USB Ethernet adapter may look modern but still contain a 100 Mbps Ethernet controller.

Likewise, inexpensive:

• USB hubs
• travel docks
• display adapters
• powerline adapters

may advertise impressive headline speeds while providing only a 10/100 Ethernet socket.

Check the specification of the Ethernet interface itself.

Don't assume:

USB-C = Gigabit Ethernet

or:

modern-looking dock = Gigabit Ethernet.

Step 7: Check Speed & Duplex

If the hardware should support Gigabit, check the adapter configuration.

Open:

Device Manager > Network adapters

Right-click the Ethernet adapter.

Choose:

Properties > Advanced

Find:

Speed & Duplex

For normal Gigabit Ethernet operation, it should generally be:

Auto Negotiation

Intel specifically recommends Auto Negotiation for its Gigabit adapters and notes that some drivers do not even present a separate 1.0 Gbps Full Duplex choice. Auto Negotiation is still capable of establishing the 1 Gbps link.

Don't Force 1 Gbps as the “Fix”

This is a common mistake.

Someone sees:

100 Mbps

and changes:

Auto Negotiation

to:

1.0 Gbps Full Duplex

That doesn't repair a damaged cable.

If the physical connection cannot support Gigabit, forcing the setting may simply cause:

• loss of connection
• unstable networking
• negotiation problems

Leave it on:

Auto Negotiation

and find out why Gigabit isn't being negotiated.

Step 8: Check the Driver

Only after testing the physical connection would I start investigating the driver.

Check:

Device Manager > Network adapter > Properties > Driver

If the problem began after a driver update, consider:

Roll Back Driver

Otherwise obtain the correct driver from:

1. Windows Update
2. computer manufacturer
3. Ethernet adapter manufacturer where appropriate

Avoid generic third-party driver-updater utilities.

A driver can affect Ethernet behaviour, but if replacing one cable instantly restores Gigabit, you don't need a new driver.

Step 9: Test Another Computer

This is another excellent isolation test.

Use the same cable and same network port with another Gigabit-capable computer.

Second computer also gets 100 Mbps

The problem is probably:

• cable
• socket
• switch
• network path

Second computer gets 1 Gbps

Investigate the original:

• Ethernet adapter
• dock
• driver
• configuration

This is much stronger evidence than repeatedly running internet speed tests.

Step 10: Don't Blame the ISP Yet

Suppose:

Broadband = 900 Mbps

Ethernet link = 100 Mbps

Speed test = 94 Mbps

Calling the ISP is unlikely to achieve much.

The internet connection may be delivering its full capability to the router.

Your local Ethernet connection is restricting the PC before it even reaches the internet.

Microsoft's Windows Ethernet troubleshooting guidance similarly recommends checking the cable and router connection as part of the first-line diagnosis.

Fix the 100 Mbps Ethernet negotiation first.

Then test broadband performance.

A Very Common Office Example

Imagine:

PC → wall socket → patch panel → Gigabit switch

Windows reports:

100 Mbps

You replace the PC patch lead.

Still 100 Mbps.

You connect the PC directly to the switch using the same computer.

Windows immediately reports:

1.0 Gbps

Now you know:

• PC supports Gigabit
• adapter works
• driver works
• switch port supports Gigabit

The fault is somewhere in:

wall socket → structured cabling → patch panel/patch lead

That is proper troubleshooting.

You have isolated the fault instead of guessing.

The Fastest Troubleshooting Order

If Windows Ethernet is stuck at 100 Mbps:

1. Confirm Windows actually reports 100 Mbps link speed.
2. Replace the cable with a known-good Cat 5e/Cat 6 cable.
3. Reseat both ends firmly.
4. Try another known Gigabit switch/router port.
5. Connect directly and bypass wall cabling.
6. Bypass the docking station.
7. Check the Ethernet adapter supports Gigabit.
8. Leave Speed & Duplex = Auto Negotiation.
9. Check the network driver.
10. Test another computer on the same cable and port.
11. Investigate structured cabling if direct connection works.
12. Only investigate the ISP once the local link negotiates correctly.

The principle is:

Physical layer first. Software later.

What Not to Do

Don't immediately:

• reinstall Windows
• disable IPv6
• change DNS
• reset the network stack
• disable TCP features
• force 1 Gbps
• install a random driver updater
• replace the router

None of those repairs a broken conductor inside an Ethernet cable.

Why This Matters More in a Business

A 100 Mbps connection might not seem disastrous for web browsing.

But it can seriously affect:

• server file transfers
• NAS access
• large Microsoft 365 uploads
• workstation backups
• imaging
• large creative files
• local database workloads

A company may spend money upgrading:

500 Mbps broadband → 1 Gbps broadband

and see absolutely no improvement on a workstation whose Ethernet connection is still negotiating at 100 Mbps.

Before buying more bandwidth, find the actual bottleneck.

How Hamilton Group Can Help

Hamilton Group can diagnose wired-network problems across the complete connection rather than assuming every slow network problem belongs to the ISP.

We can help with:

• Ethernet troubleshooting
• structured cabling
• switches
• routers
• Windows networking
• docking stations
• network adapters
• business broadband
• Wi-Fi
• network performance
• server and NAS connectivity

If one PC is stuck at 100 Mbps, we can identify why.

If an entire office has inconsistent Ethernet performance, we can investigate the network infrastructure rather than repeatedly changing Windows settings.

Visit hgmssp.com or call 0330 043 0069 to discuss business networking and IT support.