I recently signed up to NBN for my home (finally) and in the process of setting up DDNS and public ssh for my router, I notcied the WAN IP reported from my dd-wrt portal is different to my public IP. The reported WAN IP looks like 100.xxx.xxx.xxx.
Upon research, AussieBroadband now defaults new connection to use Carrier-grade NAT, instead of directly assigning you an public IPv4 address. This means your router will connect to AussieBroadband's own private subnet in the CG-NAT block allocated block 100.64.0.0/10 behind the public internet. This also means you will share the same public IP with some other households.
This would be problematic as I wanted to setup remote ssh and VPN access to my home network. Some gamers will also notice this from the Internet Connection Test of your Nitendo Switch returning NAT Type C.
Hail AussieBroadband
People on reddit and whirlpool has already sugggested simply calling AussieBroadband to request to get off CG-NAT. What surprised me was how smooth the process indeed was. No stupid triagging questions asked, the support staff got me off CG-NAT as soon as I requested that over the phone, and even offered to kick my connection to fasten the process.
Five minutes after the phone call, I release-renewed my WAN connection from my router portal, and BINGO, I now have a public IP address to use with my DDNS setup.