Why want my iptables scripts run in cron

[david <dlm4444@bigzoo.net>]

I have a simple script called routup.sh to start the routing at a certain 
time, it is excutable. It runs fine at the command line but not cron. here is 
what my cron entry looks like:                0 9 * * * root   /etc/routup.sh
#routup.sh
#!/bin/bash

echo 1 > /proc/sys/net/ipv4/ip_forward
iptables -t nat -A POSTROUTING -o eth1 -j MASQUERADE 

I even went as far to add a path to the crontab file like this:
vi crontab   

/sbin/iptables.  
where am i going wrong. 
The o.s. is linux mandrake 9.0

thanks for any help,

david