Linux – Which tool should I trust, mii-tool and ethtool don’t show me the same values

ethernetethtoolgigabit-ethernetlinux

Our hosting company provides all the switching infrastructure for our servers. The private network, connected to eth2 should be GbE. Recently I've been suspecting that something is misconfigured as cacti graphs never appear to show more than 100mbit of traffic on the link.

Digging further I found that mii-tool and ethtool do not agree on the link speed.

# mii-tool eth2
eth2: negotiated 100baseTx-FD flow-control, link ok
# ethtool eth2 
Settings for eth2:
    Supported ports: [ TP ]
    Supported link modes:   10baseT/Half 10baseT/Full 
                            100baseT/Half 100baseT/Full 
                            1000baseT/Half 1000baseT/Full 
    Supports auto-negotiation: Yes
    Advertised link modes:  10baseT/Half 10baseT/Full 
                            100baseT/Half 100baseT/Full 
                            1000baseT/Half 1000baseT/Full 
    Advertised auto-negotiation: Yes
    Speed: 1000Mb/s
    Duplex: Full

Which tool should I trust ?

Best Answer

Since mii-tool is deprecated, I'd go for ethtool. Can't you check the other sides opinion of the link speed, btw?

mii-tool and ethtool are known to disagree in certain circumstances; you can find bugreports of that on a host of websites. What driver are you using? At least tg3 is known to be a subject of disagreement between the two tools.

UPDATE: Checked it for you locally, but it seems mii-tool can only report upto 100MiB/s. ethtool is therefore probably right in your situation ;-) Must be the reason it is deprecated, anyway...

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