LINK_ADDR(3) | 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 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.

December 7, 2016 | NetBSD 9.0