From 7028c8e756129cbb7898798fc81a16de3625709f Mon Sep 17 00:00:00 2001 From: Raimo Niskanen Date: Wed, 24 Oct 2012 15:36:22 +0200 Subject: kernel: Document socket option ipv6_v6only --- lib/kernel/doc/src/inet.xml | 62 +++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 62 insertions(+) (limited to 'lib/kernel/doc') 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

+ {ipv6_v6only, Boolean} + +

+ Restricts the socket to only use IPv6, prohibiting any + IPv4 connections. This only applicable for + IPv6 sockets (option inet6). +

+

+ 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 + (setopts/2) + containing this description. +

+

+ The behaviour of a socket with this socket option set to + true 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 + {ipv6_v6only,false} 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 false. + 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. +

+

+ On some platforms the only allowed value for this option + is true, e.g. OpenBSD and Windows. Trying to set + this option to false when creating the socket + will in this case fail. +

+

+ Setting this option on platforms where it does not exist + is ignored and getting this option with + getopts/2 + returns no value. On Windows the option acually does + not exist but it is emulated as being a read-only option + with the value true. +

+

+ So it boils down to that setting this option to true + 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 false, + which might be doable (but weird) on e.g. OpenBSD. +

+

+ If you read back the option value using + getopts/2 + 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. +

+
+ {keepalive, Boolean}(TCP/IP sockets)

Enables/disables periodic transmission on a connected -- cgit v1.2.3