IPTables Strangeness

[Luke Davis]

Anyone have any idea why this happens?:

iptables -t nat -A PREROUTING -i eth0 --dport 23 -j REDIRECT --to-port 80
iptables v1.2.6a: Unknown arg `--dport'
Try `iptables -h' or 'iptables --help' for more information.
Done, exiting