LM1200 DHCP issue on new subnet

[Dashingbenjamin]

Hi all,

I have purchased an LM1200 to act as 4G failover on an existing network.
The existing network operates on the 192.168.20.0/24 subnet.

As such, the network overview is:
ISP modem -> LM1200 -> clients

However, when I put the LM1200 into router mode, and change the router’s IP to 192.168.20.254 with DHCP range of 192.168.20.220 - 250 the device restarts, and DHCP does not function.

Using wireshark I can see DHCP discover packets and no response. This is common on all clients.
If I set a manual IP in the 192.168.20.x range I get connectivity, and the settings page shows the device in router mode with DHCP enabled.

I am unable to move the device in the network overview to be before the ISP router because the ISP uses PPPOE which fails to pass through the Netgear LM1200.

My troubleshooting so far is:
- power cycle
- factory reset
- firmware upgrade
- firmware downgrade (attempted - failed)
- power cycle, apply settings, power cycle again
- tried applying .20.253/24, .21.254/24 and .22.254/24

Any help here would be appreciated!

- Ben

[plemans]

Usually with failover it goes
modem---->lm1200------>router

Not sure exactly how it works when using a combo device and the proper settings. 

Maybe one of the mods on here can help  @JohnPeng 

[Dashingbenjamin]

Ideally it’d go that way - but unfortunately the router is using PPPOE authentication which doesn’t appear to pass through the LM1200, even in bridge mode.

[mli]

Can the LM1200 DHCP service be made to function by any means at all?

E.g. by using whatever is the out-of-the-box subnet configuration such as 192.168.1.1/24 or 192.168.0.1/24 with only the router directly connected to one client.

Could small steps be then made to advance to the desired configuration to see when DHCP functionality breaks?

[Dashingbenjamin]

Hi Mli,

Only on the default subnet 192.168.5.x/24
If I change it at all, even just the third octet, it fails completely.

I tried 192.168.1.x/24, 192.168.20.x/24, 10.0.0.x/24 and none worked.

[mli]

Is it possible to leave this non-cooperative device on its default subnet and reconfigure the rest of the network to be compatible with this?

It may be that after several days, the root cause may become obvious and then you can move everything to the desired configuration.