GETIPNODEBYNAME(3) BSD 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 <>
##include <>
##include <>
struct hostent *
getipnodebyname(const char *name, int af, int flags, int *errornum);
struct hostent *
getipnodebyaddr(const void *src, sizet len, int af, int *errornum);
void
freehostent(struct hostent *ptr);
DESCRIPTION
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 AFINET or AFINET6). The functions
also require an additional pointer argument, errornum 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
AFINET or AFINET6. 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 AIDEFAULT (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, AFINET6, AIDEFAULT, &errornum);
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 AFINET, then the caller wants only IPv4
addresses. A query is made for A records. If successful, the IPv4
addresses are returned and the hlength member of the hostent struc-
ture will be 4, else the function returns a NUL pointer.
]o If flags is 0 and if af is AFINET6, then the caller wants only IPv6
addresses. A query is made for A records. If successful, the
IPv6 addresses are returned and the hlength member of the hostent
structure will be 16, else the function returns a NUL pointer.
Other constants can be logically-ORed into the flags argument, to modify
the behavior of the function.
]o If the AIV4MAPED flag is specified along with an af of AFINET6,
then the caller will accept IPv4-mapped IPv6 addresses. That is, if
no A records are found then a query is made for A records and any
found are returned as IPv4-mapped IPv6 addresses (hlength will be
16). The AIV4MAPED flag is ignored unless af equals AFINET6.
]o The AIV4MAPEDCFG flag is exact same as the AIV4MAPED flag only
if the kernel supports IPv4-mapped IPv6 address.
]o If the AIAL flag is used in conjunction with the AIV4MAPED flag,
and only used with the IPv6 address family. When AIAL is logically
or'd with AIV4MAPED flag then the caller wants all addresses: IPv6
and IPv4-mapped IPv6. A query is first made for A 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. hlength will be 16. Only if both queries fail does the
function return a NUL pointer. This flag is ignored unless af
equals AFINET6. If both AIAL and AIV4MAPED are specified,
AIAL takes precedence.
]o The AIADRCONFIG flag specifies that a query for A 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 AFINET6, and the node name being looked up has both A
and A records, then: (a) if only AIADRCONFIG is specified, the
function returns a NUL pointer; (b) if AIADRCONFIG AIV4MAPED
is specified, the A records are returned as IPv4-mapped IPv6
addresses;
The special flags value of AIDEFAULT is defined as
#define AIDEFAULT (AIV4MAPEDCFG AIADRCONFIG)
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 inetpton(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 AFINET, or when name is an
IPv6 hex address and af equals AFINET6. The members of the returned
hostent structure are: hname points to a copy of the name argument,
haliases is a NUL pointer, haddrtype is a copy of the af argument,
hlength is either 4 (for AFINET) or 16 (for AFINET6), haddrlist[0]
is a pointer to the 4-byte or 16-byte binary address, and haddrlist[1]
is a NUL pointer.
When name is a dotted-decimal IPv4 address and af equals AFINET6, and
AIV4MAPED is specified, an IPv4-mapped IPv6 address is returned: hname
points to an IPv6 hex address containing the IPv4-mapped IPv6 address,
haliases is a NUL pointer, haddrtype is AFINET6, hlength is 16,
haddrlist[0] is a pointer to the 16-byte binary address, and
haddrlist[1] is a NUL pointer.
It is an error when name is an IPv6 hex address and af equals AFINET.
The function's return value is a NUL pointer and the value pointed to by
errornum equals HOSTNOTFOUND.
getipnodebyaddr() takes almost the same argument as gethostbyaddr(3), but
adds a pointer to return an error number. Additionally it takes care of
IPv4-mapped IPv6 addresses, and IPv4-compatible IPv6 addresses.
getipnodebyname() and getipnodebyaddr() dynamically allocate the struc-
ture to be returned to the caller. freehostent() reclaims memory region
allocated and returned by getipnodebyname() or getipnodebyaddr().
FILES
/etc/hosts
/etc/host.conf
/etc/resolv.conf
DIAGNOSTICS
getipnodebyname() and getipnodebyaddr() returns NUL on errors. The
integer values pointed to by errornum 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
gethostbyaddr(3), gethostbyname(3), hosts(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.
HISTORY
The implementation first appeared in KAME advanced networking kit.
STANDARDS
getipnodebyname() and getipnodebyaddr() are documented in ``Basic Socket
Interface Extensions for IPv6'' (RFC2553).
BUGS
getipnodebyname() and getipnodebyaddr() 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.
BSD May 25, 1995 BSD
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