Adrian_456
Posts: 2
Joined: Mon Sep 17, 2018 8:06 am

Pi 3B+ Ethernet hardware behaviour

Mon Sep 17, 2018 8:39 am

Hello all,

I am a bit of a NOOB with Pi's, though I've gently used them since day 1.

The setup:
A Pi 3B+ purchased maybe a month ago from an official supplier, with a 8GB SD card, absolutely standard (and up to date) Raspian OS, with a standard keyboard and mouse plugged in to 2 USB ports. Using the official white Pi3 PSU.

My current issue / observations:

1) When connected with a short ethernet cable to a Netgear GS108T switch the ethernet socket led lights come on and the Desktop network icon shows 2-way green arrows. Ok Good.

2) When connected by approx 10-15 meters of "reasonable quality" cat5e cable from the Netgear GS108T switch the ethernet socket led lights come on and the Desktop network icon shows 2-way green arrows. Ok Good.

3) Increasing the cable distance, to approx 25 meters, then the ethernet socket led lights do NOT come on and the Desktop network icon shows red crosses. FAIL.

The max distance for ethernet cable, i believe to be 100m, so well within this.

I think that the yellow/green led's do very very faintly glow during boot, but never come alive.

I have tried exactly the same 30 meter cable using a standard PC -> all Ok and most significantly using my older Pi 2B and Pi 1. Both work perfectly.


So, am I missing something silly, or is there an issue with the 3B+ (ie possible hardware issues, or a sensitive adaptor, etc)?


I hope you can help,

Thanks,

Adrian.

PS: Sorry if I've posted this in the wrong section.

User avatar
allfox
Posts: 452
Joined: Sat Jun 22, 2013 1:36 pm
Location: Guang Dong, China

Re: Pi 3B+ Ethernet hardware behaviour

Mon Sep 17, 2018 9:21 am

They changed the Ethernet chip, so there could be anything strange between the 3B+ and those elder model. Don't know what is it.

Might worth changing the cable.

6by9
Raspberry Pi Engineer & Forum Moderator
Raspberry Pi Engineer & Forum Moderator
Posts: 7019
Joined: Wed Dec 04, 2013 11:27 am
Location: ZZ9 Plural Z Alpha, aka just outside Cambridge.

Re: Pi 3B+ Ethernet hardware behaviour

Mon Sep 17, 2018 9:42 am

Make sure that your cable has all 4 pairs correctly connected.

The 3B+ supports gigabit ethernet that requires all 4 pairs, and it does not downrate to a lower speed should it get the correct signalling on the main pair but be unable to connect on the additional pairs.

100Mbit/s ethernet, as supported on earlier Pis, only require 2 pairs.
Software Engineer at Raspberry Pi Trading. Views expressed are still personal views.
I'm not interested in doing contracts for bespoke functionality - please don't ask.

Adrian_456
Posts: 2
Joined: Mon Sep 17, 2018 8:06 am

Re: Pi 3B+ Ethernet hardware behaviour

Mon Sep 17, 2018 11:58 am

Hi all,

Thanks for these ideas.

I can confirm that all 8 cores in the cable are connected (using a cable tester). Also the PC connects at Gigabit speeds also suggesting all cores are made and are good.

I don't have another 3B+ to try.

Would anyone else have 30++ meters of ethernet cable and be happy to give the 3B+ a try on the end of it?

Thanks Adrian.

6by9
Raspberry Pi Engineer & Forum Moderator
Raspberry Pi Engineer & Forum Moderator
Posts: 7019
Joined: Wed Dec 04, 2013 11:27 am
Location: ZZ9 Plural Z Alpha, aka just outside Cambridge.

Re: Pi 3B+ Ethernet hardware behaviour

Mon Sep 17, 2018 12:18 pm

Other LAN adapters automagically downgrade to 100Mbit/s if they see initial handshaking at 1000 but fail to bring up the other pairs. Have you checked that the PC is really connecting as Gigabit?

I know that PhilE has his main Pi 3B+ connected to the main office infrastructure, and the server room is over 30m away. You may wish to try disabling the Energy Efficient Ethernet option as initially that was causing problems with longer cables. Add "dtparam=eee=off" to /boot/config.txt.
Software Engineer at Raspberry Pi Trading. Views expressed are still personal views.
I'm not interested in doing contracts for bespoke functionality - please don't ask.

Return to “General discussion”