I have searched, unsuccessfully, for any documentation on the Ethernet LEDs and asked on the Forum, but got no replies.
dtparam -h eth_led0 eth_led1 produces the following, but it is unclear what most of these mean.
eth_led0 Set mode of LED0 - amber on Pi3B+ (default "1"),
green on Pi4 (default "0").
The legal values are:
Pi3B+
0=link/activity 1=link1000/activity
2=link100/activity 3=link10/activity
4=link100/1000/activity 5=link10/1000/activity
6=link10/100/activity 14=off 15=on
Pi4
0=Speed/Activity 1=Speed
2=Flash activity 3=FDX
4=Off 5=On
6=Alt 7=Speed/Flash
8=Link 9=Activity
eth_led1 Set mode of LED1 - green on Pi3B+ (default "6"),
amber on Pi4 (default "8"). See eth_led0 for
legal values.
On a Gigabit router:-
The **Pi3B+** amber LED blinks.
The Green LED is off.
The **Pi4** amber LED is on.
The Green LED blinks.
The Pi3B amber LED is on.
The Green LED blinks.
Speed: 100Mb/s
There appears to be no consistency.
Out of curiosity I ran the command on my PiB+ running Stretch
eth_led0 Set mode of LED0 (usually orange) (default
"1"). The legal values are:
0=link/activity 1=link1000/activity
2=link100/activity 3=link10/activity
4=link100/1000/activity 5=link10/1000/activity
6=link10/100/activity 14=off 15=on
eth_led1 Set mode of LED1 (usually green) (default
"6"). See eth_led0 for legal values.