login to the R7000 (dd-wrt) router, then go to the Administrator - Commands tab (Diagnostics)
enter the following command, as shown, here, all in one
ifconfig vlan2:1 192.168.3.253 netmask 255.255.255.0
iptables -t nat -I POSTROUTING ! -s $(nvram get lan_ipaddr) -d 192.168.3.0/24 -j SNAT --to 192.168.3.253
then press (Save Startup)
every time the router boots, it will run this command, meaning even if theres a power cut, the settings will stay the same, sharme the same, cant be said about the HG612
I've tried saving the config file, then re uploading it, but it seems the settings you input in to the HG612 by telnet, don't show up in the UI, so after a rebootor power cut, the modem will always need the settings sent to it, again and again.... if anyone knows how to make it keep the settings, please share