LB2120 Invalid IP-Range for Valid Netmask


LB2120 Invalid IP-Range for Valid Netmask

Hello Netgear support,

I find myself re-visiting an old case (29339992) which was closed, and absolutely NOT to my satifaction. In fact, the final notes in the case log clearly shows that I was "dumped".

I'm raising this issue again and suggesting this be escalated to Netgear Engineering for resolution. I've tried the tech support route and all the replies suggested limited or incorrect networking knowledge.

* The Netmask of the LB2120 allows the value
* This Netmask should allow an IP range (for example) of: to (4096 IP addresses)
* The LB2120 would not accept these values: - (4094 IP addresses) (Netmask)
* I was forced to use a Netmask of and the IP range of: -
* It was suggested that I was attempting a class B schema.
* This is NOT correct as the Class C IP range begins at 192.x.y.z and extends up to 223.x.y.z (i.e., 2,097,152 IP addresses!)


There are hundreds, if not thousands, of articles on the web that define IP classes. Here's is one that clearly states the IP ranges in class A, B, and C networks:
(see tables 1.11 and 1.12)


This product is not working as it should and needs to be FIXED!!

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Re: LB2120 Invalid IP-Range for Valid Netmask

Not sure what you try to achieve. The default IP address (in the network) does act as an in-band management address the LB2120 link layer technology used in many Netgwar consumer products. 


If you are connecting a system (like a router) to the LB2120 LAN port (yes - LAN) the wireless provider network will assign an IP address and a subnet. This does allow to use the LB2120 for either a single system, unless your mobile contract does allow using a fixed assigned subnet (a rare species), or you can use the LB2120 LAN port to connect a router/security appliance.


Different from the common NAT routers, that network and the LAN port is not to connect to a LAN (a pleonasm, I know) where you have all your NATed systems. In general, there is no reason to change the LB2120 in-band management IP address (and subnet) - unless your LAN infrastructure does somehow overlap with the network.

Your use case for this product is wrong and does require a review. The LB2120 Data Sheet as well as the LB2120 Product Web Page does clearly show the intended usage for the Internet access in the WAN/Internet and optional to a broadband modem (on the LB2120 WAN port) if the 4G part is used as a fail-over only. It does not replace a common NAT router. I'm amazed the Netgear customer support was not able tp provide you with such an explanation by the way.



Last, your argumentation ref. network classes is wrong: A Class C network is always But in reality, and due to the shortage of IP addresses, the ISP and IT world has changed to classless CIDR. 


Afraid, for once nothing to fix on the Netgear side.


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