Question

1

Cat 6 Only 100mbit speed

rated 0 times [ 1] [ 0] / answers: 1 / hits: 2022 / 3 Years ago, wed, august 25, 2021, 3:23:58

I tried two different cat6 cables directly connected between my two ubuntu machines. This one I ordered online:
http://www.amazon.co.uk/gp/product/B002SQPDXS/ref=wms_ohs_product
only achieves 100mbit speeds, but does appear to be supporting cross-talk (direct pc to pc), the other cat 6 cable, worked perfectly and gets the full 1gigabit speed.

Both tests were performed using ftp and checking the network monitor with direct pc to pc connection.

Was the product description incorrect or do I need to manually set a setting somewhere in ubuntu for some cables? I had thought 10 quid for 20m of gigabit ethernet cable was a bit cheap, you get what you pay for.

Update:
It seems that after rebooting, the device is set to 1000mbit sec when looking it up with

sudo ethtool eth0

However after a while, this will drop down to just 100, after which to reset it to 1000 again, I have to reboot, and simply unplugging and re-plugging in the cable doesn't do it.

I tried setting this in networking config file as suggested here:

auto eth0

iface eth0 inet static

pre-up /usr/sbin/ethtool -s eth0 speed 1000 duplex full

but that resulted in my networking failing to start. Is there a problem with my 'auto-negotiation'? Can I manually override a setting to 1000mbit?

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sharall

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3 Years ago

answered 3 Years ago altybol · Accepted Answer

I discovered that running the following commands 'solved' my problem:

sudo ethtool -s eth0 autoneg off

sudo ethtool -s eth0 speed 1000 duplex full

I have been running the laptop for a couple of hours now and it hasn't switched down from 1gigabit (125MB/s) to 100mbit like it was before. I am assuming there is a problem with my auto-negotiation on the network. I realise, that networking speeds/issues depend on a lot of factors but it really does appear that overriding a configuration did the trick for me.

Hopefully this post will be useful to others who notice their cat6 connections start getting capped at 100mbit. There is probably another problem on the network and I have only fixed the 'symptom'.