Why do mii-tool and ethtool show different link statuses on RHEL?

Issue

• mii-tool and ethtool show the status of the link differently.

• ethtool reports a speed of 1000Mb/s on eth0 but mii-tool reports only 100 Mb/s. 

Output of mii-tool command :

eth0: 100 Mbit, full duplex, link ok

ethtool eth0 :

Settings for eth0:
      Supported ports: [MII]
      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: Half
      Port: Twisted Pair
      PHYAD: 1
      Transceiver: internal
      Auto-negotiation: on
      Supports Wake-on: g
      Wake-on: d
      Current message level: 0x000000ff (255)
      Link detected: yes