arp table timeout / how to update automatically if foreign MAC changes?

[smartTERRA NOC]

Hi there,

I have two servers running Debian Linux and keepalived, a IP fail over  
solution alike carp - with one little difference: when doing fail over  
the mac address for the failover ip address changes.

But my OpenBSD pf firewall doesn't recognize the change of the mac  
address. I have to clear the arp entry manually or have to wait for  
the time out (about 20 minutes). Same issue when moving an ip address  
from an physical server to another.

Is there a way to recognize automatically when the mac address  
changes? Doing a ping from the server to the firewall won't update the  
arp table entry. There must be a way to force the update of the arp  
table, my cisco switches have no problems with this kind of failover  
solutions :)

Regards,

Falk