LINK_ADDR(3) BSD Library Functions Manual LINK_ADDR(3)
link_addr, link_ntoa -- elementary address specification routines for link level access
Standard C Library (libc, -lc)
link_addr(const char *addr, struct sockaddr_dl *sdl);
link_ntoa(const struct sockaddr_dl *sdl);
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 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 le0:188.8.131.52.d.30 represents an ethernet address to be transmitted on the first Lance
link_ntoa() always returns a null terminated string. link_addr() has no return value (See
The link_addr() and link_ntoa() functions appeared in 4.3BSD-Reno.
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 July 28, 1993 BSD