Here are the steps just in case anyone needs.
1. Plug in ethernet to wan port on modem
2. Start up the modem
3. Connect to modem using wifi and password at back of the modem.
4. In browser type 192.168.1.1 and hit enter
5. If prompted for password enter default password 'admin' without qoutes.
6. Cancel the setup wizard.
7. Go to Settings and then Internet.
8. Choose connection type Residential Gateway.
9. Choose enable at 3rd option.
10. Choose connection type as Dynamic/ DHCP
And then select advanced settings.
11. Enter primary and Secondary DNS settings for Optus servers.
12. Set MTU to manual and set value to 1492
13. Select Save.
Now select 'Profiles' under settings -> internet -> profiles and then change first connection type to 'eth0'.
Save and reboot.
Solved! Solved: Go to Solution.