I love problems like this. Puzzles.

1. You might try turning off auto negotiation and "forcing" the link to various speeds and see how it responds, and not just the fastest speed. ( https://phoenixnap.com/kb/ethtool-command-change-speed-duplex-ethernet-card-linux)

2. Try a different switch port.

3. Check the switch's tx/rx error rates & retransmissions.

4. Check the NIC's tx/rx error rates & retransmissions.

5. Compare speed with something "link local", like _on the same ethernet segment_ , versus something past the gateway.

6. Compare trace routes into the device from various places, to trace route from the device _to_ those various places. There may be some asymmetry going on.

David

p.s. for seeing network stuff I like iptraf , and iptraf-ng

On Tue, Feb 6, 2024 at 8:08 PM Peter King via talk <talk@gtalug.org> wrote:

Hello all,

I have a computer located in the University of Toronto network which shows some odd network behaviour. For one, I have run speedtest-cli on it numerous times at various times of the day, and it consistently returns around 93Mbit upload/download. For comparison, a laptop in the same LAN seems to get 700Mbit, while a computer in a different part of the UofT network gets 900Mb/570Mb.

The NIC has a RealTek chip and uses the r8169 kernel module. Ethtool, which gives a live report, does list the card as running at 1Gb/s. But that sure isn't the speed I am getting.

This same slow computer also has problems if I reboot it remotely: most of the time it doesn't come up, though dmesg has the card detected. If I start from a cold boot rather than restart, it comes up correctly most of the time. In either case just typing in #netctl start <ethernet> starts it up just fine. I was trying to solve this problem and saw that there are several complaints along just these lines having to do with the r8169 module. Some people suggested downgrading to r8101 but that module is even older.

If the module isn't working well, that might account for the slower speeds.

Is there any way to tell? Obviously I can buy another NIC with a different chipset but don't really want to go to the trouble if there is an easier way to diagnose the difficulties.

All advice appreciated! Thanks.
-- 
Peter King			 	peter.king@utoronto.ca
Department of Philosophy
170 St. George Street #521
The University of Toronto		   (416)-946-3170 ofc
Toronto, ON  M5R 2M8
       CANADA

http://individual.utoronto.ca/pking/

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