LM1200 repeatedly dropping link

Hi everyone,

I've had quite the adventure today getting my gear up and running. I'd like to give some insight on how I've come to the same conclusion that the Netgear expert members like JohnPeng have that there is something going on with the Verizon network specifically. If you are looking for a straight answer I can't really give you one as to why, but I'd like to share my troubleshooting and coming to the conclusion I needed to move to a different 4G provider entirely. With that in mind, there is a lot to go over here so if you skip this post I understand. EDIT: I'm also going to throw in here, I know the difference in router vs bridge mode. I'd need bridge mode to work to have some ports working. But apparently even in bridge mode ports won't forward.

For an idea of my network and situation, I have recently transitioned to working hybrid, but I'll mostly be working from home. I have a fiber line built in directly to my home and I typically don't have any problems with it - however my work is critical in that I'd need a constant connection and no time to fumble through my phone and get a hotspot running. Even if my ISP is running at a 90% connectivity rate through the year if something happens in that 10% it can be very bad. I currently utilize a lot of Tp-link devices and the Omada controller software hosted on a Ubuntu VM - the ER605 is my gateway and supports load balancing and failover. I also have a dedicated Debian VM running various services. For this post it will just be called Services.

I received my LM1200 and plugged in my currently active PagePlus 4G SIM card for testing. PagePlus is a pre-pay MVNO dedicated to Verizon towers. SIM in the LM1200, put in the correct APN, plugged in my laptop directly and away it went. Cool, this connection is working. I then connected it to the ER605. At first some packets went through, then the entire network stopped and Omada complained about the LM1200 port being down completely. Sure enough I looked at the LM1200 and the LAN light isn't even on. Figured it was a bad Ethernet cable so I replaced with a known working one. Same issue.

I figured I was trying my luck with a pre-pay plan (this was before I started diving in to Google and finding this thread). I took my postpaid Verizon SIM from my iPhone and put it in to the LM1200. Same behavior as before - great with a single device, dead on the load balancer. Two for two so far. Checking online, people are talking about this and that, needing an actual data SIM vs a phone SIM or something to that effect, so I decided to add a plan to my Verizon account and add the actual IMEI of the LM1200 to it and Verizon recognized it being a Netgear device by name, fancy that. So surely, after driving to the Verizon store and getting this SIM card with a dedicated data plan, this would be the ticket right?

Nope. Same as before. Three for three here. Also to note, the LM1200 is in bridge mode and the ER605 catches an IP address through DHCP... Then the port goes down. Then it stays offline, refusing to obtain another IP address. Clearly something is wrong. Is it my network? Is it the LM1200 or the ER605? Time to narrow this down.

My first call to Verizon was as you'd expect - someone got on, heard my issue, transferred me to the help desk based in another country, I tried to explain what I was doing, they didn't understand, they actually called Netgear and dumped the call to them unbeknownst to either of us, so I spoke to the Netgear technician for a minute. Very much a help desk call, wouldn't listen when I said I was logged in to the LM1200 already, had me walk through the steps to open the browser, go to H T T P, etc.. After they gathered enough information from me, they determined the LM1200 is working as expected and terminated the call. OK then. Guess I'll take their word for now.

Back on the phone with Verizon. Figured maybe it was my internal DNS running on the Services server. While waiting for a rep I SSH'd in to the Services server and ran a packet trace pointed at UDP 53 for DNS. If anyone wants that command by the way:

tcpdump -ni (your_network_interface) udp port 53

(To find your network interface, this is typically found in /etc/network/interfaces on Debian or Ubuntu or by running "ip addr")

Testing again with one device, DNS fetching would work just fine. Suddenly when another device would get on the network, the packet dump turned in to multiple "ServFail 0/0/0 (55)" messages, even if the LM1200 managed to come back online. Unbound is a very simple DNS implementation and I use Cloudflare DNS for the forwards, so it was pretty unlikely that was down. On the other testing VM (Windows 10), I switched DNS away from my Services server and straight to Google's 8.8.8.8 - this worked for a brief moment, and then right back to the old behavior of no traffic passing at all. To me this was telling that something was actively killing the connection.

Finally getting through to another Verizon rep, I asked if they could hear me out before throwing me to help desk hell again. I had to explain the concept of failover as best as possible and what I was trying to achieve and they were super cool about it. After a minute for them to wrap their head around it, they told me the only solutions they'd really have for this is that they'd get Tier 2 on the phone and they would recommend a repeater/amplifier which is not what we'd want, or that Verizon specifically sells a mobile hotspot that will allow multiple devices. That was another tell for me that there is likely something in the terms of service saying they'd only allow one device for tunneling like this and to get around it I'd need to refund the LM1200 and add on yet another unwanted device to my Verizon plan. Told them I greatly appreciated their time and disconnected the call.

Googling deeper I found this thread, and people talking about the LM1200 and using it with T-Mobile through Google Fi, through AT&T with a data pre-pay plan - not so many hits with Verizon post-pay and pre-pay solutions. Neither of those carriers are great in my area, but I still need that backup and I had some cash to blow. Went to Best Buy, said goodbye to $70 for the Google Fi Unlimited Plus SIM card, activated, put in to the LM1200. Adjusted the APN and tadaa, working Internet to my test laptop. Threw the LM1200 back on the ER605, got an IP address just fine, killed the fiber line, tested with multiple devices, internal DNS working as expected, no problems at all. Pretty quick failover too, might I add. Other than time being wasted, I am now happy with the LM1200 and yes that plan is a bit pricey for pre-pay but I'd rather have peace of mind if something were to go down.

So here's a summary of testing:

- Tried a pre-pay Verizon SIM via PagePlus. Didn't work. Worth a shot.

- Used my current Verizon post-pay SIM from my iPhone to test. Nope, not working.

- Added a line on Verizon post-pay specific to a data plan with the LM1200's IMEI and gave that a try. No dice.

- The first time I'd seen the network port go down, I thought it could be a bad Ethernet cable. Switched to a known working cable, same result.

- Switching from internal DNS to external DNS specifically did not resolve the issue. Noted from internal DNS packet capture network would die specifically as more devices got online.

- Speaking with a good Verizon rep the idea on their end is that you get frustrated with this and just buy a mobile hotspot from them (not their words but my takeaway).

- Switching to a completely different carrier, no problems.

I'd say it is pretty conclusive at this point that Verizon does not work with the LM1200, or at least in a extremely limited capacity in that you can only have one device connected and failing over to a typical home LAN will not work. And yes, that is on Verizon and how they handle their network - however, I'd hope that Netgear recognizes this and puts a big fat asterisk on their product page noting the limitation of failover with the Verizon network. I hope someone from Netgear sees this and can update documentation, or something to that degree? I happen to live in a city with multiple phone towers, I'd still would have liked to use Verizon since they are very good here, but I can live with T-Mobile in this emergency use-case. I'd just feel bad for people with only Verizon nearby to get this and waste their time.

Also, one little side complaint - I host a VPN from home and implement Dynamic DNS to push a new WAN IP address if failover occurs to a domain name I bought. My VPN works as expected from my fiber line. However when connected to the LM1200 even in bridge mode it cannot see the required port open. I noted the IP address from the actual LM1200 and it differs from doing a Google search for my own public IP address. So I take it this isn't really a "bridge mode" then if ports cannot be opened? Any way to accomplish this? Would I have to, God forbid, turn on UPnP?

Thanks for coming to my TED talk everyone.