[clue-tech] ethtool is a lying sack of snake spittle

[Jim Ockers]

Hi David,

David L. Willson wrote:
> ethtool reports eth0 connected at Gig E full duplex, but transfer speeds over NFS, and every other test I can think of, indicate 100 Mb. Today, I looked at the switch, and it too, indicates 100Mb. What gives? Is there another, better tool for diagnosing and twiddling network settings?
>
> David L. Willson
> Trainer, Engineer, Enthusiast
> MCT MSCE Network+ A+ Linux+ LPIC-1 NovellCLA UbuntuCP
> tel://720.333.LANS
> Freeing people from the tyranny (or whatevery) of Microsofty-ness
>
>   
The problem is probably not ethtool... It is just telling you what the 
NIC driver (via SIOCETHTOOL ioctls) is telling it. So the liar might be 
the NIC driver.

Does your NIC driver support SIOCGMIIPHY ioctls or just SIOCETHTOOL 
ioctls? If so you could try /sbin/mii-tool and see if it gives different 
information. However I am inclined to think that this problem is a bug 
in the NIC driver, or the NIC driver not properly or fully supporting 
your particular NIC, which is why it might indicate erroneous link state.

What NIC (including chipset, and PCI revision) and NIC driver (kernel, 
and driver version) are you using? Are you sure it is fully supported? 
Reason I ask is a lot of the gigabit NICs go through rapid hardware 
changes and a lot of times the hardware revs and they are supposed to 
update some PCI ID or chip ID so that the driver knows about exactly 
what hardware version it is (so it knows what the registers and values 
are, etc). Maybe in your case the version of driver you are using is 
ever so slightly incompatible with the version of silicon you have.

Can you try a different kind of NIC? A different (newer) kernel version? 
Or just compile an updated driver module for your NIC and see if that helps?

HTH,
Jim

-- 
Jim Ockers, P.Eng. (ockers at ockers.net)
Contact info: http://www.ockers.ca/pason.html