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| -rw-r--r-- | lib/kernel/doc/src/inet.xml | 62 |
1 files changed, 62 insertions, 0 deletions
diff --git a/lib/kernel/doc/src/inet.xml b/lib/kernel/doc/src/inet.xml index 32b4a429dd..d0ed26a18d 100644 --- a/lib/kernel/doc/src/inet.xml +++ b/lib/kernel/doc/src/inet.xml @@ -520,6 +520,68 @@ fe80::204:acff:fe17:bf38 </p> </item> + <tag><c>{ipv6_v6only, Boolean}</c></tag> + <item> + <p> + Restricts the socket to only use IPv6, prohibiting any + IPv4 connections. This only applicable for + IPv6 sockets (option <c>inet6</c>). + </p> + <p> + On most platforms this option has to be set on the socket + before associating it to an address. Therefore it is only + reasonable to give it when creating the socket and not + to use it when calling the function + (<seealso marker="#setopts/2">setopts/2</seealso>) + containing this description. + </p> + <p> + The behaviour of a socket with this socket option set to + <c>true</c> is becoming the only portable one. The original + idea when IPv6 was new of using IPv6 for all traffic + is now not recommended by FreeBSD (you can use + <c>{ipv6_v6only,false}</c> to override the recommended + system default value), + forbidden by OpenBSD (the supported GENERIC kernel) + and impossible on Windows (that has separate + IPv4 and IPv6 protocol stacks). Most Linux distros + still have a system default value of <c>false</c>. + This policy shift among operating systems towards + separating IPv6 from IPv4 traffic has evolved since + it gradually proved hard and complicated to get + a dual stack implementation correct and secure. + </p> + <p> + On some platforms the only allowed value for this option + is <c>true</c>, e.g. OpenBSD and Windows. Trying to set + this option to <c>false</c> when creating the socket + will in this case fail. + </p> + <p> + Setting this option on platforms where it does not exist + is ignored and getting this option with + <seealso marker="#getopts/2">getopts/2</seealso> + returns no value. On Windows the option acually does + not exist but it is emulated as being a read-only option + with the value <c>true</c>. + </p> + <p> + So it boils down to that setting this option to <c>true</c> + when creating a socket will never fail except possibly + (at the time of this writing) on a platform where you + have customized the kernel to only allow <c>false</c>, + which might be doable (but weird) on e.g. OpenBSD. + </p> + <p> + If you read back the option value using + <seealso marker="#getopts/2">getopts/2</seealso> + and get no value the option does not exist in the host OS + and all bets are off regarding the behaviour of both + an IPv6 and an IPv4 socket listening on the same port + as well as for an IPv6 socket getting IPv4 traffic. + </p> + </item> + <tag><c>{keepalive, Boolean}</c>(TCP/IP sockets)</tag> <item> <p>Enables/disables periodic transmission on a connected |