Date: Fri, 15 Nov 2013 15:19:47 +0000 From: Frank Leonhardt <frank2@fjl.co.uk> To: freebsd-questions@freebsd.org Subject: Re: lagg(4) question Message-ID: <52863B93.5030903@fjl.co.uk> In-Reply-To: <201311151449.HAA04566@mail.lariat.net> References: <201311151449.HAA04566@mail.lariat.net>
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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. Regards, Frank.
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