Day: October 31, 2024

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Netgear Mifi MR5100

I’ve been carrying this device for a few years now. I think I bought it in the midst of the pandemic. It provides internet backed by the local cellular network. I’ve used MiFi’s of one form or another since the mid 1990s. In the beginning, the devices were dreadful and the service matched. This devices isn’t bad at all. One of it’s most powerful features is the ability to piggyback it’s network on the wifi provided by your hotel. I use this feature to connect a carried Apple TV in remote places.

The problem with Apple TVs on Hotel Wifi: T&C acceptance

Most hotel wifi requires you to accept terms and conditions on a splash screen before you can use the wifi. This T&C splash screen is a once per device occurance so blindly connecting an Apple TV means that you would have to accept but as far as I know, the Apple TV has no way to show this screen. If you are reading this and you know that I’m wrong, email me at chris / at / vindaloo / dot / com. I’m curious to know what works for you. I have gotten my Apple TV onto the hotel’s network by spoofing the Apple TV’s MAC address to get the Apple TV checked in as having accepted the T&C but that’s the only other way that I know how to do this.

Apple TVs really want a private broadcast domain

Apple TVs heavily advertise their existing on the local network or broadcast domain. This is totally fine in your house where you control the broadcast domain but putting an Apple TV directly onto the hotel’s network is really asking for trouble. All the hotel’s guests can see it, ask me how I know, and any hotel customers who have Apple products can attempt to use your Apple TV as a broadcast device. Now, I know for a fact that an Apple TV that’s directly connected to any modern television via HDMI can wake up, turn on the TV and start broadcasting video when asked to another Apple device. Yes, this can be prohibited by setting a password on the Apple TV but that’s a changeable setting. Finally on a private broadcast domain, this is a really useful and powerful feature.

The mifi solves both of these problems. You check the T&C screen once for the mifi and since it’s using NAT, everything behind it works. And the mifi using that NAT to create a private, local broadcast domain. Furthermore, if you join your iPhone, or iPad, or MacBook to the network created by the mifi, you can use the Apple TV as you would if you were at home.

Setting up the MR5100

The feature that you want from the Mifi is called Data Offloading. You get to choose whether to rebroadcast the internet from either local WiFi or ethernet if you are lucky enough to have working ethernet in a hotel room these days. With data offloading you choose the network you want to consume and off you go.

Data Offloading weirdness

So I’m actually writing this to document some quirks that I’ve discovered on a two week long jaunt through western Europe.

You need to bring some sort of a wireless analyzer because if you want to rebroadcast the hotel’s wifi, the Mifi’s wifi must be on and it must be set to use a different channel from the hotel. Further, if you are lucky enough to have ethernet in your room, you actually just want to use your MiFi’s network backhauled against ethernet.

  • Configuring the Mifi / Apple TV against hotel wifi: String and ethernet cable between the Mifi and the Apple TV. Configure data offloading to use wifi and to connect to the hotel’s network.
  • Configuring the Mifi / Apple TV against hotel ethernet: Connect the mifi’s ethernet port to the hotel. Configure data offloading to use ethernet. Connect your Apple TV to the mifi using your network and credentials.

This combination is useful in other ways. At one of the hotels during our stay, the wifi was very week except by the hotel room door. It turned out that I could connect the mifi to power near the door. This created a local network that I could use anywhere in the room with more reliable, but more latent, connectivity to the internet that I could get from the hotel alone. Note well that in this hotel where the wifi was strong it was awesome. In the lobby I clocked a speedtest of 200Mb/s up and down. I was able download a 9Gb virtual machine image over dinner and drinks without a problem. In our room, the wifi analyser showed nearly no 5GHz network activity and a middling to weak 2.4GHz signal except for a spot on a table about 2m (6ft) from the door. Placing the mifi on this table and using data offloading to broadcast a 5GHz network created usable signal within the room.

In conclusion

The Netgear MR5100 with data offloading is a useful device by itself. It’s essential if you want to carry an Apple TV on a long trip to keep up with your streaming. It can also help to fix wifi problems in hotels rooms where you just get blank stares from the hotel staff. But, if you are lucky, it actually really shines in a situation where you can feed it local ethernet.

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Add the watchdog timer on Raspberry pi

I learned about the kernel watchdog timer when I ran my network appliances on hardware from Soekris Engineering. The appliances should be running unless one has specifically turned them off but as the that’s not the reality of the world. A watchdog timer is something that has to be frobbed, I’ve also seen petted periodically or the kernel will assume that all of userland is borked. When userland is borked this way, the kernel will reset, hoping that a reset will kickstart enough of the userland infrastructure programs to put the system into a workable state. On Soekris, you could program the kernel watchdog to timeout of 60s. On the Pi, it looks like the maximum is 15s. Raspberry Pi’s are weird. For small jobs, the best way to run them is on SD cards.But an SD card in a Pi will die from write exhaustion after running for something between a year and two years. This is my experience based on using SanDisk 8G SD cards without any consideration for write exhaustion. You can mitigate this and lengthen the lifetime in many ways:

  • Purchase a 16G card where you have an 8G need.
  • Purchase a Pi with more RAM than you need and perform write heavy task to a memory backed filesystem or ramdisk.
  • Do all of your logging via syslog and push all your logs onto a remote log server.

On the Pi devices that I use as cameras, I write the picture / movie output to a RAM disk. I have also noticed that the older SD devices I was buying in the past were more susceptible to this problem that the devices that I buy lately. This is probably a biased observation.