lagg(4) and LACP setup

Christian Weisgerber naddy at
Tue Jul 31 22:15:13 UTC 2012

Tilman Keskinöz <arved at> wrote:

> FreeBSD -if0---------flaky link1 ----Switch----FreeBSD Router
>   |                                    |
>   if1 --------------flaky link2 ---
> I think the best configuration would be to use lagg(4) with LACP to
> catch the failing links.
> I have found several examples to do this with two completely seperate
> links both computers using lagg interfaces, but in my setup the router
> has only one interface.

LACP manages physical links.  In your setup above, you would configure
LACP on the FreeBSD host (not the router) and on the switch.  If
the switch doesn't support it, you can't use LACP.

> AFAI understood the Router needs to answer the LACP packets send by the
> lagg interface. how do i activate this on a normal ethernet card?

I think it's possible to create a lagg(4) interface on top of a
single physical interface, but that's of no use here.

You could use lagg(4) in _failover_ mode on the FreeBSD host.  This
(like LACP, actually) assumes that the availability of the link is
correctly signaled by the interface link state.  If by "flaky" you
mean that packets are simply blackholed, none of this will work.

Christian "naddy" Weisgerber                          naddy at

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