Assistance with getting WAN to work with Netgear CG3000v2 in Bridge Mode

Hi all, I'm new, have a basic knowledge of the things Im trying to achieve and despite extensive searching I'm coming up with blanks to get what should be a simple configuration working.

Basically I'm an Australian Optusnet Cable customer (yay, lucky me) and I would desperately like to see if bridging the modem I have, the Netgear Genie CG3000v2 (firmware V2.08.07) to the WAN port of my Sophos and then link my 24 port Netgear Gigabit switch to the LAN port for basic networking to the house and home office.

I have got the Sophos XG115 from my business partner and it is fully registered with Sophos and I've basically set it back to pretty basic config (though not having ever seen one from scratch I'm not too sure and it's not like you can just paper clip these guys right :P)

I've got all the firewall rules turned off as a precaution.

From what I've read there are two things I need to know to work with this Modem/Router in bridge mode.

1) Optusnet allocates it's clients' IPs via MAC address on modem so the best way to bridge the connection is to spoof the MAC on the new router.

2) Optusnet then provisions a DHCP WAN address and there is no need for any authentication or credentials.

The best and most encouraging thread I found was at whirlpool:

forums.whirlpool.net.au/.../2179609

Sounded simple enough.

So I went into the Netgear Genie Cable/Modem and took note of it's MAC address and the external IP I get (which has stuck around for a very long time now) and then switched it to bridge mode.

This means that the only way I can access the web front end of the Netgear is to connect directly to Port 1 on the LAN and hit 192.168.100.1 for admin purposes.

Only Port 1 on the Netgear will be working and wifi will be down so it should then just be a dumb modem pushing from the RG6 to Port 1 LAN.

So I put a Cat 6 patch from the Netgear Port 1 to the Port 2 WAN on the Sophos and patch the Port 1 LAN port on the Sophos to the main switch of my network.

My Sophos is available to configure on https://192.168.0.2:4444 and the Netgear was originally the default gateway at 192.168.0.1.

I started turning on DHCP and so forth but ended up abandoning all that while I tried to get the internet to work.

Something I read was that you needed to turn the new router off and back on to allow it to reconfigure itself to the new provisioning via DHCP (and I did this because it didn't work just plugging it all in and saving a new setup on the Sophos, or after rebooting the Sophos via the web admin).  This too did not work.

So I tried various things adding and removing and recreating the gateways and dipping into the routing areas, zones and such but in the end nothing got me anywhere.

I find that I can ping the Sophos, connect to it and so on but in this configuration I never get internet.

What could I be doing wrong.

I'll try to add some pics to help convey what my setup looks like...

TIA Will