I know that this is not how a true admin would do it, but this is for a small home network and for a person who's not very comfortable with the command line iptables configuration.
There's a small home network with a shared DSL connection (funny, huh? why won't everyone get his/her own DSL connection - but it is not cheap here). There's currently an Ubuntu server 8 box in front of the DSL modem to shield the modem from eventual flood (why's the flood - let's say we can't control it) and the admin would also block the internet access for some users using iptables on the server. So its a simple router + firewall configuration.
Is there any built in or freely available GUI tools to simplify network configuration on linux?
(He could switch to a desktop version of ubuntu and remote through VNC, that's not a problem and it is not a production environment so security is not that a big consideration, neither is performance.)