tera, just keep in mind that a router loses a lot of its "protective properties" if you are running bridge/half-bridge connections.
Not sure how the DNS attacks work from a technical perspective, so I don't know whether the router firewall/NAT will catch it.
The router usually runs in normal PPPoE mode set on the router itself. The times the attacks occurred I wasn't connected via half bridge either.
My logic says if a software firewall like zone alarm etc. can block the attack, so should the router. In actual fact, why pay thousands upon thousands of rands for pure hardware firewalls if the hardware isn't capable of protecting you?