CARP issue with 2 Masters

Matthew Seaman m.seaman at
Sun Oct 5 10:11:45 UTC 2008 at wrote:

> I have CARP running on a master and a slave server and for some unknown reason 
> the slave continues to classify itself as a master, even though the advskew is 
> higher than on the master. 
> It appears that queries sent to the CARP ip address go to the master 50% of the 
> time and the slave 50% of the time when both servers are up. This plays havoc 
> with my databases as I synchronise them asynchronously.
> When I take the carp interface down on the slave using 'ifconfig carp0 down && 
> ifconfig carp0 up' it lists it's status as 'backup' for about 10 seconds and 
> then goes back to 'master'.

Have you by any chance firewalled out the multicast packets that CARP uses
to test for interface death?  If either one of a CARP pair can't see CARP packets
frequently enough it will think the other is down and promote itself to master.

If your firewall is blocking, then add a rule like this on both machines:

pass quick on $ext_if proto carp \
    from $ext_if:network to $carp_mcast keep state

$carp_mcast is defined as ""



Dr Matthew J Seaman MA, D.Phil.                   7 Priory Courtyard
                                                  Flat 3
PGP:     Ramsgate
                                                  Kent, CT11 9PW

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