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Re: Ethernet suddenly limited to 100 Mbps



Vincent Lefevre wrote:
> Stan Hoeppner wrote:
> > Vincent Lefevre wrote:
> > > On my laptop, Ethernet has been limited to 100 Mbps for a few days.
> > > Nothing changed on the network side. Just a few upgrades on the laptop
> > > (Debian/unstable). Any explanation?
> > 
> > Gigabit ethernet is fully auto negotiating at the hardware level--a
> > software update shouldn't cause negotiation to drop to 100.  GBE uses
> > all 8 conductors of category 5e/6 cabling, fast ethernet uses only 4.
> > If it's negotiating to 100, I'd say you have a bad cable, connector
> > (cable or receiver port), or switch port.
> 
> The Ethernet cable was the same as before, and I've tried a second
> one, and it's still 100. I've also tried another port on the switch.

I think it would be useful to double check the settings using ethtool
to dump the current values.  Maybe there will be a clue in your
output.  Here is an example from my machine.

  # ethtool eth0
  Settings for eth0:
	Supported ports: [ TP ]
	Supported link modes:   10baseT/Half 10baseT/Full 
	                        100baseT/Half 100baseT/Full 
	                        1000baseT/Full 
	Supported pause frame use: No
	Supports auto-negotiation: Yes
	Advertised link modes:  10baseT/Half 10baseT/Full 
	                        100baseT/Half 100baseT/Full 
	                        1000baseT/Full 
	Advertised pause frame use: No
	Advertised auto-negotiation: Yes
	Speed: 1000Mb/s
	Duplex: Full
	Port: Twisted Pair
	PHYAD: 2
	Transceiver: internal
	Auto-negotiation: on
	MDI-X: on (auto)
	Supports Wake-on: pumbg
	Wake-on: g
	Current message level: 0x00000007 (7)
			       drv probe link
	Link detected: yes

I have been using 'iperf' lately for bandwidth testing.  Just getting
a GigE connection does not mean that I get full wire speeds out of it
end to end.  So it is good to have an objective tool to test.

  $ iperf -s
  ...
  [  3]  0.0-10.0 sec   904 MBytes   758 Mbits/sec

Bob

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