.\"	$NetBSD: inet6_getscopeid.3,v 1.3 2013/10/31 00:30:14 wiz Exp $
.\"-
.\" Copyright (c) 2013 The NetBSD Foundation, Inc.
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.\" This code is derived from software contributed to The NetBSD Foundation
.\" by Christos Zoulas.
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.Dd October 31, 2013
.Dt INET6_GETSCOPEID 3
.Os
.\"
.Sh NAME
.Nm inet6_getscopeid ,
.Nm inet6_putscopeid
.Nd IPv6 scope id encoding and decoding functions
.\"
.Sh SYNOPSIS
.In netinet/in.h
.Ft void
.Fn inet6_getscopeid "struct sockaddr_in6 *sin6" "int flags"
.Ft void
.Fn inet6_putscopeid "struct sockaddr_in6 *sin6" "int flags"
.\"
.Sh DESCRIPTION
These functions implement a KAME-specific extension that encodes and
decodes the scope id inside in the 3rd and 4th byte of the address,
for link-local, site-local, and multicast-link-local addresses.
The scope id helps deciding which interface is used for packets of
that type.
.Pp
Typically those two bytes are
.Dv 0
for these kinds of addresses.
The scope id is stored in network byte order.
.Pp
The
.Fn inet6_getscopeid
function retrieves the scope id from the 3rd and the 4th address bytes
(from the
.Va sin6_addr
member of
.Fa sin6 ) ,
and sets the
.Ft sin6_scope_id
from them.
It then clears the two address bytes.
.Pp
The
.Fn inet6putscopeid
function stores the scope id found in
.Ft sin6_scope_id
into the 3rd and 4th byte of the address
(into the
.Va sin6_addr
member of
.Fa sin6 ) .
It then clears the
.Va sin6_scope_id
member of
.Fa sin6 .
.Pp
The
.Fa flags
argument controls for which addresses this action is performed.
It
can be a combination of:
.Bl -bullet
.It
.Dv INET6_IS_ADDR_LINKLOCAL
.It
.Dv INET6_IS_ADDR_MC_LINKLOCAL
.It
.Dv INET6_IS_ADDR_SITELOCAL
.El
.Sh HISTORY
These functions first appeared in
.Nx 7.0 .