lagg(4) and failover

Marian Hettwer mh at
Tue Aug 12 10:52:35 UTC 2008

Hi Folks,

I'm using lagg(4) on some of our servers and I'm just wondering how the
failover is implemented.
The manpage isn't quite clear:

     failover     Sends and receives traffic only through the master port. 
                  the master port becomes unavailable, the next active port
                  used.  The first interface added is the master port; any
                  interfaces added after that are used as failover devices.

What is meant by "becomes unavailable"? Is it just the physical link which
needs to become unavailable to trigger a failover?

I do wonder, because there might be other faults where the link is still
active, but the port is unusable. Think of a wrong vlan on the switch

When using bonding under Linux (yeah, I know, the configuration sucks ;) ),
I can configure the device to check for arp respones of it's default
gateway. If arp to the default gw becomes unavailable, bonding fails over
to the next interface and tries it luck over there.
With that kind of configuration, I could cover a misconfigured switch port
and still have failover.

Long Story short: How is failover in lagg(4) implemented?

Thanks for any hints :)

Or should I ask the OpenBSD boys, since lagg(4) seems to be a port of
trunk(4)?? :)

best regards,

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