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From: @(#)linkaddr.3 8.1 (Berkeley) 7/28/93
$FreeBSD$
.Dd February 28, 2007 .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 n sys/types.h n sys/socket.h n 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.
p 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.
p
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
The
.Fn link_ntoa
function
always returns a null terminated string.
The
.Fn link_addr
function
has no return value.
(See
.Sx BUGS . )
.Sh SEE ALSO
.Xr getnameinfo 3
.Sh HISTORY
The
.Fn link_addr
and
.Fn link_ntoa
functions appeared in
x 4.3 Reno . .Sh BUGS
The returned values for link_ntoa
reside in a static memory area.
p The function .Fn link_addr should diagnose improperly formed input, and there should be an unambiguous way to recognize this.
p 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.