How can I tell if my home printer is securely protected? Is there a good web page or text book anyone can recommend that will teach me more details about this? Thanks.
In a home network you typically have a router that separates your LAN (local area network) from the internet and shares one public IP among the devices in your network; in that case you have little to worry about. You can tell by the kinds of IP addresses your devices have: if it starts with 192.168.x.y, 172.x.y.z, or 10.x.y.z, then it's not reachable from the internet. The problem with these printers is that on their network there's no such separation and they are listening on a publicly routed IP address, but they've been designed with the tacit assumption that they will be used on a secured network.
Depends. Some builds of Tomato (Toastman's for sure) put a firewall up on IPv6 by default. Asus's firmware does NOT firewall IPv6 at all. If you have shell access to your router, I suggest putting up a firewall on IPv6. The following should work (change br0 to the bridged LAN interface and eth0 to the WAN interface, sometimes it's a vlan):
ip6tables -A FORWARD -m state --state RELATED,ESTABLISHED -j ACCEPT
ip6tables -A FORWARD -i eth0 -o br0 -p all -j DROP
ip6tables -A FORWARD -i br0 -j ACCEPT
ip6tables -A FORWARD -o br0 -j ACCEPT
ip6tables -A FORWARD -j DROP
Of course insert whatever open ports you want after the first line.