lagg(4) and failover

Peter Jeremy peterjeremy at
Tue Dec 9 01:02:12 PST 2008

Please wrap your mail before 80 columns.
On 2008-Dec-08 23:58:00 -0800, Tom Samplonius <tom at> wrote:
>  The Linux bonding driver supports probing the default gateway.

This is the same brokenness as Solaris IPMP.  I agree that probing
an external IP address (probably, but not necessarily a gateway) is
the way to go but you need to be able to configure this.  Otherwise
you need to jump through hoops where the interfaces you are protecting
is not the default route (or there are multiple independent groups
of interfaces being protected).

>  Now, it uses ARP for this (probably because the ARP who-has code is
>also in the kernel and easily accessible), which also not so great,

I don't see that it's necessary to have the interface failover code
in the kernel.  The kernel needs hooks to allow a daemon to bind to
the physical interfaces and control which one is active, but the
actual code that decides how to determine which interface is active
should be in userland.  (Note that routing works this way).

>switches do not support multi-switch 802.3ad yet, and most probably
>never well.  So you are limited to a single switch.  So 802.3ad is
>good only for aggregation, and not for high availability.

Keep in mind that higher-end switches as well as stacked lower-end
switches have a reasonable amount of internal redundancy so 802.3ad
within one distinct components of one physical switch may be adequate
for many purposes.  Keep in mind that you'll still need multiple
FreeBSD boxes to prevent them being a single point of failure.

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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