NETGEAR LB2120 Mini Review

The NETGEAR LB2120 is a small 4G LTE modem with an optional fail safe mode to switch to 4G connectivity when the wired connection goes down. For this purpose there are two Ethernet RJ45 connectors on the device. One that connects to your internal network such as a wired switch, Wi-Fi AP or router and one that may be connected to a device that provides external wired connectivity (such as an ADSL modem).

This review is based on a unit with a firmware updated on 2020-08-18. The web GUI for the device is quite spartan and does not reveal the exact firmware version that it’s running.

My home network consists of a NETGEAR Orbi Wi-Fi router and satellite. I like the Orbis because they provide both solid Wi-Fi access and have quite some ports for wired devices. Prior to acquiring the LB2120 the Orbi router was connected to an ADSL modem, obtaining the public IP address via DHCP. When an operator here in Sweden made an offer for unlimited 4G broadband access to a lower price than the ADSL connection I decided to jump ship.

The LB2120 can operate in bridge or router mode. In bridge mode the modem simply assigns the obtained 4G IP address to the first device that asks for it by a DHCP request. I originally intended to use the bridge mode as the router mode of the Orbi has more features than the LB2120. It would work just like with the old ADSL modem, handing the external IP to the Orbi router. This is where the first problem cropped up though. Even if both the LB2120 and the Orbi are NETGEAR products there seems to be some DHCP incompatibility between them in this mode. I did not have the possibility to capture network traffic between the LB2120 and the Orbi to understand exactly what went wrong but frequently the Orbi would fail to route traffic after about a day. Sometimes the problem would be alleviated by renewing the DHCP lease on the Orbi LAN port using the web GUI. One consideration is that in bridge mode there is really just one IP address that the modem can hand out via DHCP so it matters that both parties honor lease times etc. I performed a test to see if the modem would hand out the single IP to another requesting party, it did not. Personally I think that in bridge mode the modem could just assign the external IP to whoever asks for it. It would not be in accordance with the DHCP protocol but it only makes sense to have a single device connected to the modem in bridge mode anyway. So just assigning the IP to whoever asks for it would seem more robust to me considering equipment that is not up to spec.

After some weeks of this nonsense I decided to try my fortune at running the LB2120 in router mode and setting the Orbi to AP (access point) mode. This solved the perceived DHCP problems. However another more subtle problem appeared. Some web connections would be reset sometimes (often only particular domain names), or only partially render such as when the web browser fails to load CSS files from the web server. To give concrete examples, would often partially render with bonkers layout, would frequently fail to load at all. Two things provided a work around to this problem. Setting up a VPN tunnel (NordVPN) would cause both these web sites to load properly. Resetting the modem would also make these web sites load properly for a day or so before the problem reappearing. To me these symptoms indicate that something is wrong with the LB2120 NAT code.

I probably ran the modem in this mode for around 2 months before fine combing the Web GUI settings for possible solutions. Finally i tried setting “VPN Passthrough” to Off which seems to solve the issue for me.

This is what the user manual says about VPN Passthrough.

If a device that is connected to the modem functions as a VPN client for a VPN endpoint on the Internet,encrypted VPN packets are sent to the modem. Because the modem filters the encrypted packets through Network Address Translation (NAT), the packets become invalid if you do not enable VPN pass-through.By default, when the modem functions in Router mode, VPN pass-through is enabled.

Well, I don’t consider myself a networking export but not a complete novice either. I don’t understand a word of that. The first sentence indicates an outgoing VPN connection which plain NAT should handle just fine. NAT does not care if packet payload data is encrypted, it only looks at packet headers. I’m sure it’s good for something but the user manual does not explain it clearly IMHO. Anyway, NordVPN works fine from within my network with VPN Passthrough set to Off so hopefully this is where my troubles with this device ends.

Final Words

I’ve only reviewed my intended use of this device. It does have some other capabillities which I will never use. I bought it as a 4G modem and do not intend to use the failover mechanism. I have only used the internal antenna which works fine in my area (after moving the Orbi router and modem from the basement to the top floor).

I do think this product fills an important hole in the consumer oriented networking segment. There does not seem to exist other similar products which is strange because the feature set is so obviously needed for those lacking wired internet.

Unfortunately my exposure to a limited software feature set has left me with the impression that it’s “buggy as hell”. Nothing that a firmware update can’t solve but there are no such guarantees.

User manual:

Published: 2020-08-24