Info about link failure detection

[john152@libero.it]

Hello,
Í'd need an help for this problem:

i'd like to have a mechanism able to detect instantaneously a link failure between two computers each with an ethernet card and with Linux software.

Is there a software that do so?
If threre is a software, where does it bring the failure information from?
Are there Ethernet card or mechanisms that detect when a link is down in real time?
Is there a Linux ability that is able to do this?

Thanks in advance for your kind answer.

Giovanni di Giacomo