Test a Network Cable and Port Before Buying a New One

**LinkSpeed** is what the two ends agreed on, not what the adapter supports. A 1 Gbps-capable port at 100 Mbps means at least one pair is faulty.

Get-NetAdapter | Select-Object Name,InterfaceDescription,Status,LinkSpeed,FullDuplex,MediaType
Get-NetAdapterHardwareInfo | Select-Object Name,Slot,PcieLinkSpeed,PcieLinkWidth
Get-NetAdapterAdvancedProperty -Name 'Ethernet' | Where-Object DisplayName -match 'Speed|Duplex' | Select-Object DisplayName,DisplayValue

CRC and alignment errors mean the signal is bad, not the driver. A clean counter after a large transfer is the evidence that a cable is fine.

Get-NetAdapterStatistics -Name 'Ethernet' | Select-Object ReceivedBytes,SentBytes,ReceivedPacketErrors,OutboundPacketErrors,ReceivedDiscardedPackets
Get-NetAdapterStatistics -Name 'Ethernet'
Start-Sleep -Seconds 60
Get-NetAdapterStatistics -Name 'Ethernet'

Errors often appear only under load. Copy a large file to a second machine while sampling the counters, which turns a suspicion into a measurement.

1..5 | ForEach-Object { Get-NetAdapterStatistics -Name 'Ethernet' | Select-Object @{n='t';e={Get-Date -Format HH:mm:ss}},ReceivedPacketErrors,OutboundPacketErrors; Start-Sleep -Seconds 10 }
# during the loop, copy a multi-GB file to the other machine

Cable, port on the PC, port on the switch. Changing two at once hides which one was faulty, which is the whole point of the test.

# step 1: same port, new cable
Get-NetAdapter -Name 'Ethernet' | Select-Object LinkSpeed
# step 2: same cable, other port on the switch
Get-NetAdapter -Name 'Ethernet' | Select-Object LinkSpeed
# step 3: another device on the same cable and port
Get-NetAdapter -Name 'Ethernet' | Select-Object LinkSpeed,Status

The switch reports the same negotiation and its own error counters. A port that flaps between speeds has a physical fault that a driver update will not fix.

# switch web UI or console: port status, speed, duplex, CRC errors
Get-NetAdapterVmq -Name 'Ethernet' -ErrorAction SilentlyContinue | Select-Object Enabled
Get-NetAdapter | Select-Object Name,LinkSpeed,Status,MacAddress

A cable that only works at 100 Mbps is still usable for a printer or a low-traffic port. Label it and keep it out of the gigabit paths.

Get-NetAdapter | Select-Object Name,LinkSpeed,DriverVersion | ConvertTo-Json | Set-Content "$env:USERPROFILE\link.json"
Get-Content "$env:USERPROFILE\link.json"
Get-NetAdapterStatistics | Select-Object Name,ReceivedPacketErrors,OutboundPacketErrors