5G Modem as WAN connection, NAT issues..

[cakeman]

Could really use some help here, I'm a practiced amateur but I'm more screwed up that I can currently figure out.

Diagram of what I've got goin on here: https://imgur.com/a/VL9c5yQ

"Net A" - My cell provider only provides private IPs. If I bypass the "Net A" OPNsense box and go straight from client to 5G modem, the client either gets an IP (10.x.x.x) from my provider, if modem DHCP off, or one from the modem (192.168.254.x) if DHCP is on. The client then has internet access with no problems.

The modem is currently in Wireless Broadband mode vs Bridge mode. I'm not clear what Wireless Broadband mode is. I have tried it in Bridge previously with no improvement. There is essentially no decent manual available for the 5G modem that I can find.

If I plug the OPNSense box into the 5G modem, it'll get a WAN IP from the modem (or my provider, depending on DHCP) but seems to lose the IP frequently if I refresh the connections Overview page in OPNsense.

Clients get their IP's from OPNSense DHCP, on a different subnet from anything else in the chain. 192.168.1.x, generally.

In this configuration, I have no access to the internet from clients. I can ping 8.8.8.8 from a client but it returns errors from Gateway at 192.168.1.1 and then every 3-5 failed pings, returns a ping from 8.8.8.8.

In order to mostly eliminate the chance of any weird settings I've made in the last couple years running this firewall, I have reset all settings to defaults, hasn't helped.

Eventual plan is the VPN from Net A to Net B.. but should probably focus on getting Net A to work first.

thanks.

[bartjsmit]

My cell provider only provides private IPs

It looks like your 5G provider uses CGNAT 

Tailscale would work though