I have a Mega board and a GSM shield. I'm using Arduino's example "TestWebServer". The serial monitor shows that the GSM is connected, and returns a IP.

However, the IP is always 10.X.X.X. Isn't that a internal network IP address? How should I get the SIM cards IP? Thanks!

1 Answer 1


The SIM card does not have an IP address. When the data connection is made to your GSM APN it is assigned an IP in a similar way to DHCP. Often the address is the same after the first connection as the service provider will link that to your SIM for audit purposes. If you setup a private APN then you can arrange to have specific range allocated to your SIM card(s). This is normally only done for security of volume reasons.

  • I end up using bot.whatismyipaddress.com API to query the external URL address..... Plus just found out that my SIM cannot not work as a web server....
    – MW_hk
    Apr 22, 2014 at 9:25

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