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All Rights Reserved .\" Copyright 2018 Nexenta Systems, Inc. .\" .Dd July 22, 2018 .Dt INET 3C .Os .Sh NAME .Nm inet , .Nm inet6 , .Nm inet_ntop , .Nm inet_pton , .Nm inet_aton , .Nm inet_addr , .Nm inet_network , .Nm inet_makeaddr , .Nm inet_lnaof , .Nm inet_netof , .Nm inet_ntoa .Nd Internet address manipulation .Sh LIBRARY .Lb libc .Sh SYNOPSIS .In sys/types.h .In sys/socket.h .In netinet/in.h .In arpa/inet.h .Ft const char * .Fo inet_ntop .Fa "int af" .Fa "const void *addr" .Fa "char *cp" .Fa "size_t size" .Fc .Ft int .Fo inet_pton .Fa "int af" .Fa "const char *cp" .Fa "void *addr" .Fc .Ft int .Fo inet_aton .Fa "const char *cp" .Fa "struct in_addr *addr" .Fc .Ft in_addr_t .Fo inet_addr .Fa "const char *cp" .Fc .Ft in_addr_t .Fo inet_network .Fa "const char *cp" .Fc .Ft struct in_addr .Fo inet_makeaddr .Fa "const int net" .Fa "const int lna" .Fc .Ft in_addr_t .Fo inet_lnaof .Fa "const struct in_addr in" .Fc .Ft in_addr_t .Fo inet_netof .Fa "const struct in_addr in" .Fc .Ft char * .Fo inet_ntoa .Fa "const struct in_addr in" .Fc .Sh DESCRIPTION The .Fn inet_ntop and .Fn inet_pton functions can manipulate both IPv4 and IPv6 addresses. The .Fn inet_aton , .Fn inet_addr , .Fn inet_network , .Fn inet_makeaddr , .Fn inet_lnaof , .Fn inet_netof , and .Fn inet_ntoa functions can only manipulate IPv4 addresses. .Pp The .Fn inet_ntop function converts a numeric address into a string suitable for presentation. The .Fa af argument specifies the family of the address which can be .Dv AF_INET or .Dv AF_INET6 . The .Fa addr argument points to a buffer that holds an IPv4 address if the .Fa af argument is .Dv AF_INET . The .Fa addr argument points to a buffer that holds an IPv6 address if the .Fa af argument is .Dv AF_INET6 . The address must be in network byte order. The .Fa cp argument points to a buffer where the function stores the resulting string. The application must specify a non-NULL .Fa cp argument. The .Fa size argument specifies the size of this buffer. For IPv6 addresses, the buffer must be at least 46-octets. For IPv4 addresses, the buffer must be at least 16-octets. To allow applications to easily declare buffers of the proper size to store IPv4 and IPv6 addresses in string form, the following two constants are defined in .In netinet/in.h : .Bd -literal #define INET_ADDRSTRLEN 16 #define INET6_ADDRSTRLEN 46 .Ed .Pp The .Fn inet_pton function converts the standard text presentation form of a function to the numeric binary form. The .Fa af argument specifies the family of the address. Currently, the .Dv AF_INET and .Dv AF_INET6 address families are supported. The .Fa cp argument points to the string being passed in. The .Fa addr argument points to a buffer where the function stores the numeric address. The calling application must ensure that the buffer referred to by .Fa addr is large enough to hold the numeric address, at least 4 bytes for .Dv AF_INET or 16 bytes for .Dv AF_INET6 . .Pp The .Fn inet_aton , .Fn inet_addr , and .Fn inet_network functions interpret character strings that represent numbers expressed in the IPv4 standard .Ql \&. notation, returning numbers suitable for use as IPv4 addresses and IPv4 network numbers, respectively. The .Fn inet_makeaddr function uses an IPv4 network number and a local network address to construct an IPv4 address. The .Fn inet_netof and .Fn inet_lnaof functions break apart IPv4 host addresses, then return the network number and local network address, respectively. .Pp The .Fn inet_ntoa function returns a pointer to a string in the base 256 notation .Ql d.d.d.d . See the following section on IPv4 addresses. .Pp Internet addresses are returned in network order, bytes ordered from left to right. Network numbers and local address parts are returned as machine format integer values. .Ss IPv6 Addresses There are three conventional forms for representing IPv6 addresses as strings: .Bl -enum .It The preferred form is .Ql x:x:x:x:x:x:x:x , where the .Li x No 's are the hexadecimal values of the eight 16-bit pieces of the address. For example, .Ql 1080:0:0:0:8:800:200C:417A . .Pp It is not necessary to write the leading zeros in an individual field. There must be at least one numeral in every field, except when the special syntax described in the following is used. .It It is common for addresses to contain long strings of zero bits in some methods used to allocate certain IPv6 address styles. A special syntax is available to compress the zeros. The use of .Ql :: indicates multiple groups of 16 bits of zeros. The .Ql :: may only appear once in an address. The .Ql :: can also be used to compress the leading and trailing zeros in an address. For example, .Ql 1080::8:800:200C:417A . .It The alternative form .Ql x:x:x:x:x:x:d.d.d.d is sometimes more convenient when dealing with a mixed environment of IPv4 and IPv6 nodes. The .Li x No 's in this form represent the hexadecimal values of the six high-order 16-bit pieces of the address. The .Li d No 's represent the decimal values of the four low-order 8-bit pieces of the standard IPv4 address. For example: .Bd -literal ::FFFF:129.144.52.38 . ::129.144.52.38 .Ed .Pp The .Ql ::FFFF:d.d.d.d and .Ql ::d.d.d.d pieces are the general forms of an IPv4-mapped IPv6 address and an IPv4-compatible IPv6 address. .Pp The IPv4 portion must be in the .Ql d.d.d.d form. The following forms are invalid: .Bd -literal ::FFFF:d.d.d ::FFFF:d.d ::d.d.d ::d.d .Ed .Pp The .Ql ::FFFF:d form is a valid but unconventional representation of the IPv4-compatible IPv6 address .Ql ::255.255.0.d . .Pp The .Ql ::d form corresponds to the general IPv6 address .Ql 0:0:0:0:0:0:0:d . .El .Ss IPv4 Addresses Values specified using .Ql \&. notation take one of the following forms: .Bd -literal d.d.d.d d.d.d d.d d .Ed .Pp When four parts are specified, each part is interpreted as a byte of data and assigned from left to right to the four bytes of an IPv4 address. .Pp When a three-part address is specified, the last part is interpreted as a 16-bit quantity and placed in the right most two bytes of the network address. The three part address format is convenient for specifying Class B network addresses such as .Ql 128.net.host . .Pp When a two-part address is supplied, the last part is interpreted as a 24-bit quantity and placed in the right most three bytes of the network address. The two part address format is convenient for specifying Class A network addresses such as .Ql net.host . .Pp When only one part is given, the value is stored directly in the network address without any byte rearrangement. .Pp With the exception of .Fn inet_pton , numbers supplied as parts in .Ql \&. notation may be decimal, octal, or hexadecimal, as specified in C language. For example, a leading .Ql 0x or .Ql 0X implies hexadecimal. A leading .Ql 0 implies octal. Otherwise, the number is interpreted as decimal. .Pp For IPv4 addresses, .Fn inet_pton accepts only a string in standard IPv4 dot notation .Ql d.d.d.d . .Pp Each number has one to three digits with a decimal value between 0 and 255. .Pp The .Fn inet_addr function has been obsoleted by .Fn inet_aton . .Sh RETURN VALUES The .Fn inet_aton function returns nonzero if the address is valid, .Li 0 if the address is invalid. .Pp The .Fn inet_ntop function returns a pointer to the buffer that contains a string if the conversion succeeds. Otherwise, .Dv NULL is returned. Upon failure, .Va errno is set to .Er EAFNOSUPPORT if the .Fa af argument is invalid or .Er ENOSPC if the size of the result buffer is inadequate. .Pp The .Fn inet_pton function returns .Li 1 if the conversion succeeds, .Li 0 if the input is not a valid IPv4 dotted-decimal string or a valid IPv6 address string. The function returns .Li -1 with .Va errno set to .Er EAFNOSUPPORT if the .Fa af argument is unknown. .Pp The value .Dv INADDR_NONE , which is equivalent to .Li (in_addr_t)(-1) , is returned by .Fn inet_addr and .Fn inet_network for malformed requests. .Pp The functions .Fn inet_netof and .Fn inet_lnaof break apart IPv4 host addresses, returning the network number and local network address part, respectively. .Pp The function .Fn inet_ntoa returns a pointer to a string in the base 256 notation .Ql d.d.d.d , described in the section on IPv4 addresses. .Sh MT-LEVEL .Sy Safe .Sh INTERFACE STABILITY The .Fn inet_ntop , .Fn inet_pton , .Fn inet_aton , .Fn inet_addr , and .Fn inet_network functions are .Sy Committed . The .Fn inet_lnaof , .Fn inet_makeaddr , .Fn inet_netof , and .Fn inet_network functions are .Sy Obsolete Committed . .Sh SEE ALSO .Xr inet.h 3HEAD , .Xr gethostbyname 3NSL , .Xr getipnodebyname 3SOCKET , .Xr getnetbyname 3SOCKET , .Xr hosts 4 , .Xr networks 4 , .Xr attributes 5 .Sh NOTES The return value from .Fn inet_ntoa points to a buffer which is overwritten on each call. This buffer is implemented as thread-specific data in multithreaded applications. .Pp IPv4-mapped addresses are not recommended. .Sh BUGS The problem of host byte ordering versus network byte ordering is confusing. .Pp A simple way to specify Class C network addresses in a manner similar to that for Class B and Class A is needed.