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Entry in Wikipedia about NIC-bonding (active-backup):

Active-backup (active-backup) Only one NIC slave in the bond is active. A different slave becomes active if, and only if, the active slave fails.

When NIC1(master) and NIC2(slave) are in a bond/team and NIC1 fails, how does NIC2 know about this?

mushr00mer1990
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  • Do you have hardware in-hand (or in a design document) that you're asking about? – mfinni Mar 17 '15 at 15:24
  • I am configuring a bond right now with multiple NICs. I was asking myself and googled for it. Does NIC2 check the voltage of NIC1 or does it check if NIC1 doesnt answer anymore? What does "fails" actually mean in this context? – mushr00mer1990 Mar 17 '15 at 15:33
  • This could be answered by a simple Google search for your question title ([First result](http://www.enterprisenetworkingplanet.com/linux_unix/article.php/3850636/Understanding-NIC-Bonding-with-Linux.htm), [Second result](https://www.kernel.org/pub/linux/kernel/people/marcelo/linux-2.4/Documentation/networking/bonding.txt)) - It is all explained in the NIC Bonding documentation, and on MANY websites... – voretaq7 Mar 19 '15 at 18:03

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For heaven's sake. If you had clicked through the reference link on that portion of the Wikipedia article, you would have found out how the linux bonding driver does link monitoring.

http://www.linuxfoundation.org/collaborate/workgroups/networking/bonding#Link_Monitoring

  • The ARP monitor relies on the device driver itself to verify that traffic is flowing. In particular, the driver must keep up to date the last receive time, dev->last_rx, and transmit start time, dev->trans_start. If these are not updated by the driver, then the ARP monitor will immediately fail any slaves using that driver, and those slaves will stay down

...

  • The MII monitor monitors only the carrier state of the local network interface. It accomplishes this in one of three ways: by depending upon the device driver to maintain its carrier state, by querying the device's MII registers, or by making an ethtool query to the device.
mfinni
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