frank2 at fjl.co.uk
Fri Nov 15 15:19:53 UTC 2013
On 15/11/2013 14:49, Brett Glass wrote:
> I'm interested in using lagg(4) to provide failover from a main
> wireless link to a backup link. Unfortunately, one of the common
> failure modes, when a link fails, is for the Ethernet port on the
> radio to stay up but not pass any traffic. Does lagg(4) test the link,
> by actually trying to send packets, to determine if the link has
> failed? Or does it rely upon the Ethernet link losing "carrier"?
> --Brett Glass
I'm pretty sure you're right. lagg (aka truck) determines if an
interface is working by checking its "up" flag in the link_state flags
field; it also checks the firewall's idea. I stand to be corrected, but
I think it's only the interface driver's responsibility to check for a
carrier, not to "down" itself it's its not getting data through when the
hardware layer looks healthy.
If we're right in our assumption, you could always have a cron job ping
through the main wireless link, and if it fails to get a response you
could fail it (down it with ifconfig), triggering lagg. Or you could
just as easily ignore lagg and reconfigure the interfaces yourself.
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