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GETIPNODEBYNAME(3)     FreeBSD Library Functions Manual	    GETIPNODEBYNAME(3)

NAME
     getipnodebyname, getipnodebyaddr, freehostent -- nodename-to-address and
     address-to-nodename translation

LIBRARY
     Standard C	Library	(libc, -lc)

SYNOPSIS
     #include <sys/types.h>
     #include <sys/socket.h>
     #include <netdb.h>

     struct hostent *
     getipnodebyname(const char	*name, int af, int flags, int *error_num);

     struct hostent *
     getipnodebyaddr(const void	*src, size_t len, int af, int *error_num);

     void
     freehostent(struct	hostent	*ptr);

DESCRIPTION
     The getipnodebyname() and getipnodebyaddr() functions are very similar to
     gethostbyname(3), gethostbyname2(3) and gethostbyaddr(3).	The functions
     cover all the functionalities provided by the older ones, and provide
     better interface to programmers.  The functions require additional	argu-
     ments, af,	and flags, for specifying address family and operation mode.
     The additional arguments allow programmer to get address for a nodename,
     for specific address family (such as AF_INET or AF_INET6).	 The functions
     also require an additional	pointer	argument, error_num to return the
     appropriate error code, to	support	thread safe error code returns.

     The type and usage	of the return value, struct hostent is described in
     gethostbyname(3).

     For getipnodebyname(), the	name argument can be either a node name	or a
     numeric address string (i.e., a dotted-decimal IPv4 address or an IPv6
     hex address).  The	af argument specifies the address family, either
     AF_INET or	AF_INET6.  The flags argument specifies	the types of addresses
     that are searched for, and	the types of addresses that are	returned.  We
     note that a special flags value of	AI_DEFAULT (defined below) should han-
     dle most applications.  That is, porting simple applications to use IPv6
     replaces the call

	hptr = gethostbyname(name);

     with

	hptr = getipnodebyname(name, AF_INET6, AI_DEFAULT, &error_num);

     Applications desiring finer control over the types	of addresses searched
     for and returned, can specify other combinations of the flags argument.

     A flags of	0 implies a strict interpretation of the af argument:

     +o	 If flags is 0 and af is AF_INET, then the caller wants	only IPv4
	 addresses.  A query is	made for A records.  If	successful, the	IPv4
	 addresses are returned	and the	h_length member	of the hostent struc-
	 ture will be 4, else the function returns a NULL pointer.

     +o	 If flags is 0 and if af is AF_INET6, then the caller wants only IPv6
	 addresses.  A query is	made for AAAA records.	If successful, the
	 IPv6 addresses	are returned and the h_length member of	the hostent
	 structure will	be 16, else the	function returns a NULL	pointer.

     Other constants can be logically-ORed into	the flags argument, to modify
     the behavior of the function.

     +o	 If the	AI_V4MAPPED flag is specified along with an af of AF_INET6,
	 then the caller will accept IPv4-mapped IPv6 addresses.  That is, if
	 no AAAA records are found then	a query	is made	for A records and any
	 found are returned as IPv4-mapped IPv6	addresses (h_length will be
	 16).  The AI_V4MAPPED flag is ignored unless af equals	AF_INET6.

     +o	 The AI_V4MAPPED_CFG flag is exact same	as the AI_V4MAPPED flag	only
	 if the	kernel supports	IPv4-mapped IPv6 address.

     +o	 If the	AI_ALL flag is used in conjunction with	the AI_V4MAPPED	flag,
	 and only used with the	IPv6 address family.  When AI_ALL is logically
	 or'd with AI_V4MAPPED flag then the caller wants all addresses: IPv6
	 and IPv4-mapped IPv6.	A query	is first made for AAAA records and if
	 successful, the IPv6 addresses	are returned.  Another query is	then
	 made for A records and	any found are returned as IPv4-mapped IPv6
	 addresses.  h_length will be 16.  Only	if both	queries	fail does the
	 function return a NULL	pointer.  This flag is ignored unless af
	 equals	AF_INET6.  If both AI_ALL and AI_V4MAPPED are specified,
	 AI_ALL	takes precedence.

     +o	 The AI_ADDRCONFIG flag	specifies that a query for AAAA	records	should
	 occur only if the node	has at least one IPv6 source address config-
	 ured and a query for A	records	should occur only if the node has at
	 least one IPv4	source address configured.

	 For example, if the node has no IPv6 source addresses configured, and
	 af equals AF_INET6, and the node name being looked up has both	AAAA
	 and A records,	then: (a) if only AI_ADDRCONFIG	is specified, the
	 function returns a NULL pointer; (b) if AI_ADDRCONFIG | AI_V4MAPPED
	 is specified, the A records are returned as IPv4-mapped IPv6
	 addresses;

     The special flags value of	AI_DEFAULT is defined as

	#define	 AI_DEFAULT  (AI_V4MAPPED_CFG |	AI_ADDRCONFIG)

     We	noted that the getipnodebyname() function must allow the name argument
     to	be either a node name or a literal address string (i.e., a dotted-dec-
     imal IPv4 address or an IPv6 hex address).	 This saves applications from
     having to call inet_pton(3) to handle literal address strings.  When the
     name argument is a	literal	address	string,	the flags argument is always
     ignored.

     There are four scenarios based on the type	of literal address string and
     the value of the af argument.  The	two simple cases are when name is a
     dotted-decimal IPv4 address and af	equals AF_INET,	or when	name is	an
     IPv6 hex address and af equals AF_INET6.  The members of the returned
     hostent structure are: h_name points to a copy of the name	argument,
     h_aliases is a NULL pointer, h_addrtype is	a copy of the af argument,
     h_length is either	4 (for AF_INET)	or 16 (for AF_INET6), h_addr_list[0]
     is	a pointer to the 4-byte	or 16-byte binary address, and h_addr_list[1]
     is	a NULL pointer.

     When name is a dotted-decimal IPv4	address	and af equals AF_INET6,	and
     AI_V4MAPPED is specified, an IPv4-mapped IPv6 address is returned:	h_name
     points to an IPv6 hex address containing the IPv4-mapped IPv6 address,
     h_aliases is a NULL pointer, h_addrtype is	AF_INET6, h_length is 16,
     h_addr_list[0] is a pointer to the	16-byte	binary address,	and
     h_addr_list[1] is a NULL pointer.

     It	is an error when name is an IPv6 hex address and af equals AF_INET.
     The function's return value is a NULL pointer and the value pointed to by
     error_num equals HOST_NOT_FOUND.

     The getipnodebyaddr() function takes almost the same argument as
     gethostbyaddr(3), but adds	a pointer to return an error number.  Addi-
     tionally it takes care of IPv4-mapped IPv6	addresses, and IPv4-compatible
     IPv6 addresses.

     The getipnodebyname() and getipnodebyaddr() functions dynamically allo-
     cate the structure	to be returned to the caller.  The freehostent() func-
     tion reclaims memory region allocated and returned	by getipnodebyname()
     or	getipnodebyaddr().

FILES
     /etc/hosts
     /etc/nsswitch.conf
     /etc/resolv.conf

DIAGNOSTICS
     The getipnodebyname() and getipnodebyaddr() functions returns NULL	on
     errors.  The integer values pointed to by error_num may then be checked
     to	see whether this is a temporary	failure	or an invalid or unknown host.
     The meanings of each error	code are described in gethostbyname(3).

SEE ALSO
     getaddrinfo(3), gethostbyaddr(3), gethostbyname(3), getnameinfo(3),
     hosts(5), nsswitch.conf(5), services(5), hostname(7), named(8)

     R.	Gilligan, S. Thomson, J. Bound,	and W. Stevens,	Basic Socket Interface
     Extensions	for IPv6, RFC2553, March 1999.

STANDARDS
     The getipnodebyname() and getipnodebyaddr() functions are documented in
     ``Basic Socket Interface Extensions for IPv6'' (RFC2553).

HISTORY
     The implementation	first appeared in KAME advanced	networking kit.

BUGS
     The getipnodebyname() and getipnodebyaddr() functions do not handle
     scoped IPv6 address properly.  If you use these functions,	your program
     will not be able to handle	scoped IPv6 addresses.	For IPv6 address
     manipulation, getaddrinfo(3) and getnameinfo(3) are recommended.

     The text was shamelessly copied from RFC2553.

FreeBSD	10.1			August 6, 2004			  FreeBSD 10.1

NAME | LIBRARY | SYNOPSIS | DESCRIPTION | FILES | DIAGNOSTICS | SEE ALSO | STANDARDS | HISTORY | BUGS

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