Everything in this manual to date refers to IP4 (Ip version 4) addressing. The world is running out of IP4 addresses and has been for some time. Various strategies have been adotpted by ISPs to obscure this issue adn much of the world is still running on IPv4.
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Nonetheless IP6/v6 addresses will have to be used at soem furtre point. FOr now, all in the base SME Server is in IP4.