Subject: Re: CARP Committed (correctly presented)
To: None <>
From: David Young <>
List: current-users
Date: 05/19/2006 12:52:54
On Thu, May 18, 2006 at 10:18:45AM -0600, Herb Peyerl wrote:
> On 18-May-06, at 10:12 AM, Jeff Rizzo wrote:
> >I'm not familiar with keepalived, but what CARP does is to present a
> >separate floating MAC address common to all the redundant  
> >interfaces to
> >the upstream, so failover occurs as soon as the carp-implementing
> >interfaces decide amongst themselves that it should.
> That seems like it would have the same problem then.  The upstream  
> switch will still have associated the virtual mac address with a  
> physical port and the only way it will know the mac address has moved  
> to a different physical port is to wait for some sort of traffic from  
> the new master.  Though I'm just talking out of my posterior orifice  
> at this point... Maybe this works better in practice.

In general, it doesn't sound to me like it should work.  I figure it
works 9 times out of 10 by chance: some packet just happens to update the
switch's forwarding table in enough time that you don't notice a hiccup.

hostapd sends a "802.2 Type 1 LLC XID Update" to update a switch's
forwarding table when a wireless client moves from one AP to another.
See src/dist/hostapd/iapp.c.  I believe CARP should send the same type
of update.


David Young             OJC Technologies      Urbana, IL * (217) 278-3933