LINK_ADDR(3)

NAME
link_addr, link_ntoa - elementary address specification routines for link level access

LIBRARY
libc

SYNOPSIS
#include <sys/types.h>
#include <sys/socket.h>
#include <net/if_dl.h>
void
link_addr(const char *addr, struct sockaddr_dl *sdl);
char *
link_ntoa(const struct sockaddr_dl *sdl);

DESCRIPTION
The routine link_addr() interprets character strings representing link-level addresses, returning binary information suitable for use in system calls. The routine link_ntoa() takes a link-level address and returns an 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.

Prior to a call to link_addr(), sdl->sdl_len must be initialized to the size of the link-level socket structure, typically sizeof(struct sockaddr_dl).

For link_addr(), the string addr may contain an optional network interface identifier of the form “name unit-number”, suitable for the first argument to 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.

Thus le0:8.0.9.13.d.30 represents an ethernet address to be transmitted on the first Lance ethernet interface.

RETURN VALUES
link_ntoa() always returns a null terminated string. link_addr() has no return value (See BUGS).

SEE ALSO
ethers(3), iso(4)

HISTORY
The link_addr() and link_ntoa() functions appeared in 4.3BSD Reno.

BUGS
The returned string for link_ntoa() resides in a static memory area. If it would overflow this area, link_ntoa() silently truncates the result.

The function link_addr() should diagnose improperly formed input, and there should be an unambiguous way to recognize this.

If the sdl_len field of the link socket address sdl is 0, link_ntoa() will not insert a colon before the interface address bytes. If this translated address is given to link_addr() without inserting an initial colon, the latter will not interpret it correctly.