There are plenty of howtos about that, but none of them seems to match current state of DD-WRT firmware. So I decided to write my own.
You should now see the network, but you will have to manualy set IP address and you will get no internet.
ath0.1) and tweak the other settings if you want.
You should now get assigned IP address after connecting to the network. But still no internet.
iptables -I FORWARD -i ath0.1 -d `nvram get lan_ipaddr`/`nvram get lan_netmask` -j logdrop iptables -t nat -I POSTROUTING -o br0 -s 10.0.0.0/24 -j MASQUERADE iptables -I INPUT -i ath0.1 -j logdrop iptables -I INPUT -i ath0.1 -p udp --dport 67 -j ACCEPT iptables -I INPUT -i ath0.1 -p udp --dport 53 -j ACCEPT iptables -I INPUT -i ath0.1 -p tcp --dport 53 -j ACCEPT
ath0.1 and maybe
br0 with your settings!
It enables port forwarding, but disable access from guest network to your home network, except DNS and DHCP.
You should now have separate Wi-Fi network with internet access.