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.\"     From: @(#)linkaddr.3    8.1 (Berkeley) 7/28/93

.\"     $Id: linkaddr.3,v 1.2 2001-09-27 12:01:53 chris Exp $

.\"

.Dd June 17, 1996

.Dt LINK_ADDR 3

.Os BSD 4.4

.Sh NAME

.Nm link_addr ,

.Nm link_ntoa

.Nd elementary address specification routines for link level access

.Sh SYNOPSIS

.Fd #include 

.Fd #include 

.Fd #include 

.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

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.

.Pp

The direct use of these functions is deprecated in favor of the

.Xr addr2ascii 3

interface; however, portable programs cannot rely on the latter as it is

not yet widely implemented.

.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 addr2ascii 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 values for link_ntoa

reside in a static memory area.

.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.