A1 Telekom Austria uses internal IPs (10.x.x.x) for traffic between UMTS and DSL

December 25, 2011

When I tried to connect from my mobile phone to my DSL router at home and had tcpdump running on the router at the same time I though there is something wrong. I saw connection requests from an 10.62.35.x IP address from the Internet. My router was of course dropping these packets, as this IP address cannot arrive on the Internet uplink interface.

After some checking I realized that my mobile phone is the 10.62.35.x source address, and I needed to accept packets from on the Internet with the source address within the range of 10.62.0.0/16. It is good that I don’t use 10.62.0.0/16 subnets at home …. but if someone does, he has a problem. 😉

Anyway has anyone more information which 10.x.x.x IP addresses the A1 Telekom Austria (and Bob for my mobile) does use?

ps: The DSL router has a worldwide IP address but the mobile IP is local, surely to force businesses into more expensive plans to have a worldwide IP address. 😉

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