Bridge a Netgear C6300BD (Telstra Gateway Max) to a Telstar Smart Modem Gen 2 DHCP returns wrong default gateway address

The set up is :

1. Telstra Smart Modem Gen 2 Main Router connected to internet 192.168.100.2 DHCP 192.168.100.3-239 2.4GHZ Wifi (not reliably working) 5GHZ Wifi (working) 4 Eth ports working (1 used to connect to other router) Clients connecting directly to this router are served correct DHCP information.

Specifically the default gateway is 192.168.100.2

2. Telstra Gateway Max Netgear C6300BD NAT disabled (places router in bridge mode) 192.168.100.1 (fixed, can't be changed) 2.4GHZ Wifi (working) 5GHZ Wifi (working) 4 Eth ports working (1 used to connect to other router) Clients connecting to this router are served nearly correct DHCP information. Everything is correct except the default gateway which is 192.168.100.1

Ok my initial problem was my Smart modem stopped reliably working on the 2.4GHZ band.

I bridged the Gateway Max just for that purpose.

The Gateway Max has restricted bridging capabilities as when placed in bridge mode the IP is fixed.

This meant re-configuring the Smart Modem to work with the Gateway Max's address constraints.

I found this worked but clients would be given the wrong default gateway when connecting via the Gateway Max and would be given the Gateway Max's address instead of the Smart modem's address which is where the DHCP server is situated.

[EDIT] It appears the wrong default gateway is given to all clients. After reconnecting a client the gateway was incorrect for all!

So clients require manual IP setup in order to work.

Since there is no configuration on the Smart Modem in relation to setting up the bridge I was surprised the DHCP default gateway address was being changed.

I'm interested to know if anyone knows a fix for this?

[Further]

I didn't like having to manually configure all my clients so I changed it all back. That was when I noticed the default gateway was wrong again and was set to 192.168.100.2 !!! Even though the the router was set for 192.168.0.1.

It's like the default gateway setting lags behind the actual changes configured via the interface. Or maybe I should have reset the device between each change. The router probably only figures out the default gateway address during the boot (base on the current router address) in which case changing the router address wont update the default gateway until the next reboot/reset.

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