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FreeBSD 11.0 - man page for link_addr (freebsd section 3)

LINK_ADDR(3)						   BSD Library Functions Manual 					      LINK_ADDR(3)

NAME
link_addr, link_ntoa -- elementary address specification routines for link level access
LIBRARY
Standard C Library (libc, -lc)
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 sys- tem 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. 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 sepa- rated 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
The link_ntoa() function always returns a null terminated string. The link_addr() function has no return value. (See BUGS.)
SEE ALSO
getnameinfo(3)
HISTORY
The link_addr() and link_ntoa() functions appeared in 4.3BSD-Reno.
BUGS
The returned values for link_ntoa reside in a static memory area. 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.
BSD
February 28, 2007 BSD