#!/bin/sh

list="gre gre-bridge gre-multipoint ipip sit ipip6 ip6ip6"
full_list="${list}"
if [[ -n "$1" ]]; then
	for f in ${full_list}; do if [[ "$1" = "$f" ]]; then exit 0; fi; done
	echo "Must be (${full_list})"
	exit 1;
else
	echo ${full_list}
fi