CARP using Serial to sync

[Brandon Mercer <nomercy_(_at_)_eutonian_(_dot_)_com>]

Hello,
Is it possible to use a serial cable to "heartbeat" two openbsd 
firewalls together using CARP rather than the third ethernet 
connection?  I realize that quite a bit of information probably passes 
along that path with states and the like and that a serial connection 
may not be able to keep up... but I was curious.  What I had wanted to 
do was setup a DMZ type situation using a soekris box with three 
ethernet connection and use the serial connection as the "heartbeat."  
Thanks,
Brandon