.\"	$NetBSD: linkaddr.3,v 1.12 2016/12/07 03:48:05 pgoyette Exp $
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.\"     @(#)linkaddr.3	8.1 (Berkeley) 7/28/93
.\"
.Dd December 7, 2016
.Dt LINK_ADDR 3
.Os
.Sh NAME
.Nm link_addr ,
.Nm link_ntoa
.Nd elementary address specification routines for link level access
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In sys/types.h
.In sys/socket.h
.In net/if_dl.h
.Ft void
.Fn link_addr "const char *addr" "struct sockaddr_dl *sdl"
.Ft char *
.Fn link_ntoa "const struct sockaddr_dl *sdl"
.Sh DESCRIPTION
The routine
.Fn link_addr
interprets character strings representing link-level addresses,
returning binary information suitable for use in system calls.
The routine
.Fn link_ntoa
takes a link-level address and returns an
.Tn ASCII
string representing some of the information present, including the
link level address itself, and the interface name or number, if present.
This facility is experimental and is still subject to change.
.Pp
Prior to a call to
.Fn link_addr ,
.Fa sdl-\*[Gt]sdl_len
must be initialized to the size of the link-level socket structure,
typically
.Fa sizeof(struct sockaddr_dl) .
.Pp
For
.Fn link_addr ,
the string
.Fa addr
may contain
an optional network interface identifier of the form
.Dq "name unit-number" ,
suitable for the first argument to
.Xr ifconfig 8 ,
followed in all cases by a colon and
an interface address in the form of
groups of hexadecimal digits
separated by periods.
Each group represents a byte of address;
address bytes are filled left to right from
low order bytes through high order bytes.
.Pp
.\" A regular expression may make this format clearer:
.\" .Bd -literal -offset indent
.\" ([a-z]+[0-9]+:)?[0-9a-f]+(\e.[0-9a-f]+)*
.\" .Ed
.\" .Pp
Thus
.Li le0:8.0.9.13.d.30
represents an ethernet address
to be transmitted on the first Lance ethernet interface.
.Sh RETURN VALUES
.Fn link_ntoa
always returns a null terminated string.
.Fn link_addr
has no return value (See
.Sx BUGS ) .
.Sh SEE ALSO
.Xr ethers 3 ,
.Xr iso 4
.Sh HISTORY
The
.Fn link_addr
and
.Fn link_ntoa
functions appeared in
.Bx 4.3 Reno .
.Sh BUGS
The returned string for
.Fn link_ntoa
resides in a static memory area.
If it would overflow this area,
.Fn link_ntoa
silently truncates the result.
.Pp
The function
.Fn link_addr
should diagnose improperly formed input, and there should be an unambiguous
way to recognize this.
.Pp
If the
.Va sdl_len
field of the link socket address
.Fa sdl
is 0,
.Fn link_ntoa
will not insert a colon before the interface address bytes.
If this translated address is given to
.Fn link_addr
without inserting an initial colon,
the latter will not interpret it correctly.