ethtool and map ip to nic server

[HenryChuaka]

Hi guys,

I am trying to use ethtool to detect whether cable has been connected to a nic remotely. But I realize the link sense = yes with or without cable connected. This is the first time I see this, is there something enwrong?

Also generally how do u know which ethN is which NIC?

Regards
Henry

[Matti_Kurkela · Accepted solution]

> But I realize the link sense = yes with or without cable connected.

What's your NIC model? If the Linux driver for that NIC is very new, it might not include a working version of the link detection yet.

Or if the hardware manufacturer has made a new revision of existing hardware and changed the way the link detection works, the change might not be included in your version of the Linux driver yet.

Or if you're using blade hardware (e.g. HP c-class blades) with a switch module integrated into the blade chassis, the link sense might be telling you that yes, the internal connection between the blade and the switch module is most definitely connected. In that case, you need to use the switch module management tools to check the link states of external connections.

> Also generally how do u know which ethN is which NIC?

Generally? You test it when installing the server for the first time and document it.

The command "ethtool -p " might be useful in this: it will cause the LED(s) of the port to blink in some recognizable way until the command is aborted, or for a specified time. For example, "ethtool -p eth0 10" will blink the LED(s) of port eth0 for 10 seconds.

Most Linux distributions today have a system that assigns ethN numbers persistently to NICs by their MAC addresses; so, if you add a new NIC later, the already-allocated ethN numbers won't change.

(On the other hand, if your NIC fails and you need to replace it, you'll need to know which configuration file to modify in order to make the replacement NIC take the ethN number of the failed one...)

MK

[HenryChuaka]

Thanks MK!