Production use of carp?

Jeremy Chadwick freebsd at
Thu Jun 2 22:49:05 UTC 2011

On Fri, Jun 03, 2011 at 12:10:36AM +0200, Patrick Lamaiziere wrote:
> Le Thu, 2 Jun 2011 16:39:40 -0400,
> John <jwd at SlowBlink.Com> a ?crit :
> Hello,
> >    However, if system A is the MASTER, and system B is rebooted,
> > the carp interface on system A will flip/flop going down and
> > coming back up which is not what I want.
> I saw this if the switch connecting the two systems takes some time to
> forward packets when a link is "up". This happens if the switch is doing
> some spanning tree protocol. (on cisco swith you should use an option
> "spanning tree port fast" on the switch port to avoid this)

Expanding a bit on this:

This is written oddly (to me anyway).  What Patrick's referring to is
classic STP (Spanning Tree Protocol) taking a long time to deal with
link negotiation, and for you to consider using RSTP (Rapid Spanning
Tree Protocol) instead.  This advice doesn't apply if spanning tree
isn't enabled on your switches; whether or not it is by default is
unknown to us.  Please refer to your switch documentation and/or vendor.

Alternately, depending on the model of switch used, there are other
protocols which can cause this behaviour as well.  One such protocol is
LLDP (Link Layer Discovery Protocol).  I ran into this issue on our HP
ProCurve switches; disabling LLDP ("no lldp run") solved slow link

Other such protocols link disovery protocols are EDP, NDP (SONMP) and
LLTD.  Turn them all off if you don't need them.

| Jeremy Chadwick                                   jdc at |
| Parodius Networking              |
| UNIX Systems Administrator                   Mountain View, CA, US |
| Making life hard for others since 1977.               PGP 4BD6C0CB |

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