Ok, took most of my Sunday evening, but I believe I’m now up and running again with the RUTX50 in Passthrough mode, with stable internet through to my ER605 (where DHCP is/should be performed), and Internet provided to all clients at all permitted VLANs on my Omada network.
I worked up a substantial Word document log of steps taken with associated before/after screenshots, but I think the big hitter in all of this was applying the MAC address of the ER605 WAN port (which I can confirm is the hardware printed sticker MAC address incremented up by one) to the mob1s1a1 WAN Interface setting page.
I got a good couple days running in NAT mode, and switching to Passthrough mode with ‘DHCP Disabled: On’ (mob1s1a1 WAN Interface page) still allowed Internet at the main VLAN on my Omada setup, but instantly blocked it on all other Omada VLANs. Then, setting ‘DHCP Disabled: Off’ but adding the MAC address to the configuration brought all VLANs back online instantly, so while I still don’t fully understand the reason, this has 99% returned me to my original working configuration. The only difference now is that I have to create a static WAN port IP address on my ER605 on the same subnet as the RUTX50 LAN port, and DHCP is presumably ‘enabled’ on the RUTX50 (but directed to the ER605) whereas before it wasn’t, and doesn’t seem to be doing anything anyway as my VLANs are all on a completely different subnet.
Just to reaffirm my own networking knowledge here, if I put ANY mobile router into Passthrough mode, shouldn’t all DHCP capability be switched off if I want it to just act as a dumb 5G modem? This was my understanding and is what I’ve done with our previous two iterations of cellular internet sources on the same SIM card (a Netgear Nighthawk M1 and a TP-Link Archer MR600), and also how I ran the RUTX50 for over a year with no issues until Firmware 07.09.1.
I expect there are some use cases where DHCP in Passthrough at the cellular hardware are valid, otherwise why not just disable it automatically by default and grey out the option when Passthrough is selected. But for me, I have a pre-configured Omada network that just asks for an internet source connected to its only active WAN port, and it is/was setup to do so regardless of the cellular passthrough device connected to it, or at least given my experience always has. Therefore, what is the reason (outside of my probable lack of understanding) for turning the ‘DHCP Disabled: Off’ slider on my RUTX50 (to make entering a MAC address available), when the ER605 should be doing the DHCP? And… why has this only become an issue now?
I can see that the DHCP Server page of the RUTX50 gives the default 100 through 249 pool of dynamic addresses, none of which are being used because the static address on the ER605 is in the sub-100 range, and DHCP on both IPv4 & IPv6 tabs are set to ‘Status: Disabled’ anyway with nothing else ever to be connected on the same RUTX50 LAN/ER605 WAN subnet, so I’m confused… Is setting ‘DHCP Disabled: Off’ just to get the GUI option for MAC address and disabling it manually needs to be done throughout the rest of the device, or is it actually switched on but serving no function at the moment other than to provide unrequired DHCP for 100 to 249 on its own subnet?
My Omada network uses a completely different subnet address range to the RUTX50 (outside of the now static WAN port), and the VLANs are split again into their own subnets. So, I’m sure all DHCP is being done at the Omada level… Isn’t it?
I’m obviously going to do some more reading outside of these questions to help my understanding, maybe book myself that CompTIA course I’ve been telling myself I always would, but for now I’m up and running again (13hrs, plus a successful scheduled weekly reboot) with a configuration I’m happier with, so the pressure is off.
Thanks again to you Mike for the suggestion as it seems to have been the solution, even if I don’t yet fully understand the fix!
Kind Regards,
Leon.