288さん、これ見た？

#!/bin/sh
# Script to check if pppoe interface is down and, if so, restart it
state=`/sbin/ifconfig pppoe0 | /usr/bin/grep 0.0.0.0`
if [ "x$state" != "x" ];then
/bin/echo "Restarting PPPoE connection"
/sbin/ifconfig pppoe0 down
/sbin/ifconfig pppoe0 up
fi

NetBSD has ifwatchd, which monitors network interfaces and optionally
executes scripts when the interface is brought up or down.
I've used an equivalent shell script on Solaris using PPPoE for several
years with no problems, and so far so good with OpenBSD as well
- I don't see any need for an additional daemon (ifwatchd) to handle
such a simple task.
つまりifwatchdなんていらないって書いてるよ