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In my Fibre Optic device (Linux 2.6.27, LXT971A PHY Transceiver), connection to the port is lost intermittently. While debugging with ETHtool, the following observation was observed:

Settings for eth0: Supported ports: [ TP MII ] Supported link modes: 10baseT/Half 10baseT/Full 100baseT/Half 100baseT/Full Supported pause frame use: No Supports auto-negotiation: Yes Advertised link modes: 10baseT/Half 10baseT/Full 100baseT/Half 100baseT/Full Advertised pause frame use: No Advertised auto-negotiation: Yes Speed: 1000Mb/s Duplex: Full Port: MII PHYAD: 0 Transceiver: external Auto-negotiation: off Link detected: yes

The Switch used (ruggedcom) supports only 100Mb/s FULL DUPLEX . Why is the speed moved to 1000Mb/s and the link detected is "yes" ? After this stage is reached the port will not try any other speed and stays in 1000Mb/s until device restart. Please note that the issue is observed only with a FO cable of length 30m or more and works fine with FO cable of length 2m.

Any comments or insights are greatly appreciated.

  • The BMCR and BMSR are in the following Modes: BMCR = 2100 (100Mbps,full duplex) BMSR = 780D – karthikkumar Nov 14 '17 at 6:37
  • You need to add hardware details. The Intel LXT971A is a 10BASE-T/100BASE-TX copper transceiver. Are you using fiber or twisted pair?? – Zac67 Jan 19 '18 at 7:25

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