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With copper Ethernet you can see if there's a physical link even when the NIC is unused, i.e. is not configured with IP. With copper, 'ethtool ens802s0f0' will tell you "Link detected: yes" or "Link detected: no." This is not true of SFP+ interfaces, at least in the farm I support.

My question is, how can I quickly test the physical condition or state of this a fibre connection without configuring it, without assigning an IP address? All of the fibre NICs in the network are physically wired to a switch but some are unconfigured on the host. Also, there may or may not be a port configured on the Cumulus switch at the other end of the cable.

Thanks for any advice.

mr.zog
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  • please be more specific what test you wanna do.. currently the question is too broad – djdomi Mar 15 '22 at 20:05
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    I don't know what specificity you're looking for. – mr.zog Mar 16 '22 at 16:51
  • exactly - that's the issue - we don't understand your question. – djdomi Mar 17 '22 at 07:17
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    `ethtool` should work no matter if the connection is copper or fiber. The physical medium is at a level below what `ethtool` is capable of determining. – doneal24 Mar 18 '22 at 20:32
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    Yes, I know that ethtool works with copper and fibre. ethtool can tell me whether the NIC exists but it makes the interface look physically broken when it's just unconfigured. _Or is it?_ – mr.zog Mar 19 '22 at 00:25
  • I have exactly this issue as well on Centos 7 on Dell R6415. ethtool reports the interface with no link but the iDRAC shows the NIC as "Mellanox ConnectX-4 LX 25GbE SFP Adapter" and ports with "Link Status" Up and "Switch Port Connection ID" Ethernet18. – David Bernard Aug 26 '22 at 02:22
  • please update the question due i dont get the point what is the business related question in or issue here – djdomi Aug 27 '22 at 18:20
  • Please edit your question to include the actual output of `ethtool` for your fiber interface when the link is up. – Tilman Schmidt Aug 27 '22 at 18:47
  • You might want to take a look at the `ethtool` switch `-m --dump-module-eeprom --module-info` and the output that generates. If the driver and module support it, the optical diagnostic information is also read and decoded by ethtool. That might show you things like the receiver signal power. – HBruijn Aug 27 '22 at 18:55

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