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I was playing around with my Samsung TV trying to hide other network UPnP/DLNA devices such as Sonos speakers from showing up as source inputs on the TV.

I figured I would manually configure my TV to be on a separate subnet from those other devices but I ended up just setting a manual IP address (192.168.1.66) and subnet mask of 255.255.255.255 along with the gateway IP (192.168.1.1) and it actually works!! I can’t understand how or why.

The DLNA devices are no longer showing up as inputs and more importantly the internet is still working on the TV. How can the internet be working if a subnet mask of 255.255.255.255 only allows for one host which should mean that my TV shouldn’t be able to reach the gateway.

I guess I’d like to understand how or why it’s working.

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Subnet mask and a gateway are not fancy magic things. They just sets some "automatic" routes.

When you configure, say, 192.168.1.5/24, all it does it installs a corresponding route like 192.168.1.0/24 via NIC, where NIC is your network card.

When you also specify a default gateway, say, 192.168.1.1, it just adds a route like default via 192.168.1.1 or, in more explicit form, 0.0.0.0/0 via 192.168.1.1. Notice you gain access to the gateway itself with the help of previous "subnet mask" route, for this to happen gateway must belong to the configured subnet.

But you can add all routes explicitely! You might add address with the mask /32, then install a device route to your gateway system (in Linux: ip route add 192.168.1.1 dev NIC) and then install a route to internet through the gateway (in Linux: ip route add default via 192.168.1.1), your internet would work, despite the fact you are used the /32 net mask.

Probably, something like this is happening in your network.

Another possibility is to set up default route to the internet directly via NIC, i.e. ip route add default dev NIC, but I don't sure if such route could work on the TV with it's stripped down operating system. But such route could work in Mikrotik, Cisco and so on.

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  • Thanks. It looks like this is being done behind the scenes by the device itself. When I try this on a Windows computer I get the warning message “The default gateway is not on the same network segment (subnet) that is defined by the IP address and subnet mask. Do you want to save this configuration?” Yet it still works. I tried on an iPhone and it behaves the same way.
    – Chauncy Peppertooth
    Jan 23, 2021 at 21:24
  • I reworded an answer to be more clear why gateway must belong to the netmask and that is just sets another route that you may set by hand. (I'm so used to it that I forget it needs to be explained, sorry.) If you are following my recipe in Windows, you don't specify gateway in the GUI at first. Also notice I don't know how to set "device route" in Windows", you have to figure that out.
    – Nikita Kipriyanov
    Jan 24, 2021 at 14:20

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