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Date:      Tue, 12 Aug 2008 21:24:30 +1000
From:      Peter Jeremy <peterjeremy@optushome.com.au>
To:        Eugene Grosbein <eugen@kuzbass.ru>
Cc:        stable@freebsd.org, Marian Hettwer <mh@kernel32.de>
Subject:   Re: lagg(4) and failover
Message-ID:  <20080812112430.GC64458@server.vk2pj.dyndns.org>
In-Reply-To: <20080812105552.GA89695@svzserv.kemerovo.su>
References:  <a588673badeccac53d23f7964c216f62@localhost> <20080812105552.GA89695@svzserv.kemerovo.su>

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On 2008-Aug-12 18:55:52 +0800, Eugene Grosbein <eugen@kuzbass.ru> wrote:
>On Tue, Aug 12, 2008 at 12:37:15PM +0200, Marian Hettwer wrote:
>
>> I'm using lagg(4) on some of our servers and I'm just wondering how the
>> failover is implemented.

As far as I can tell, not especially well :-(.  It doesn't seem to detect
much short of layer 1 failure.  In particular, shutting down the switch
port will not trigger a failover.

>> The manpage isn't quite clear:
>>=20
>>      failover     Sends and receives traffic only through the master por=
t.=20
>> If
>>                   the master port becomes unavailable, the next active p=
ort
>> is
>>                   used.  The first interface added is the master port; a=
ny
>>                   interfaces added after that are used as failover devic=
es.
>>=20
>> What is meant by "becomes unavailable"? Is it just the physical link whi=
ch
>> needs to become unavailable to trigger a failover?

It seems to be,

>Yes. It seems you need lacp protocol described later in the manual.

Actually, lacp and failover are used differently: lacp is primarily
used to increase the bandwidth between the host and the switch whilst
failover is used for redundancy.

With lacp, all the physical interfaces must be connected to a single
switch.  With failover, the physical interfaces will normally be
connected to different switches (so a failure in one switch will not
cause the loss of all connectivity.

--=20
Peter Jeremy
Please excuse any delays as the result of my ISP's inability to implement
an MTA that is either RFC2821-compliant or matches their claimed behaviour.

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