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I have a cellular router that currently has a 3G SIM card plugged into it. I'd like to be able to access the devices behind my router by sending and receiving data over cellular WAN.

As a first step, I'd simply like to be able to ping my router by the cellular ip address from a remote machine and verify "reach-ability".

The cellular ip address is dynamically assigned, but that's fine for this test.

Much to my surprise, the ping did not work:

Pinging 32.178.x.y with 32 bytes of data:
Request timed out.
Request timed out.
Request timed out.
Request timed out.

Ping statistics for 32.178.x.y:
    Packets: Sent = 4, Received = 0, Lost = 4 (100% loss),

Next, I tried a tracert to see where the failure was occurring:

Tracing route to mobile-32-178-x-y.mycingular.net [32.178.x.y]
over a maximum of 30 hops:

  1     *        *        *     Request timed out.

Is this not a public ip address from my provider? Why would this address not be reachable?

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It's reachable, it just doesn't reply to ping requests. Why should it? What benefit would that provide?

I think you're under the mistaken assumption that this IP address is assigned to you. It's not. It's assigned to a NAT/gateway device. Devices on the cellular network have private IP addresses. They have to share public IPv4 addresses when they access the public Internet because such addresses are so scarce and there are so many mobile devices.

Thus traffic has to originate on the cellular side and cannot possibly originate from the Internet side as there would be no way to determine which customer was the intended destination. If you want to communicate with a device on a cellular network, you really want to have that device initiate a connection to a server that relays the data. You may be able to use a VPN or IPv6 solution too.

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