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IPSEC_TTOADDR(3)								 IPSEC_TTOADDR(3)

NAME
       ipsec_ttoaddr,  ipsec_tnatoaddr, ipsec_addrtot, ipsec_ttosubnet, ipsec_subnettot - convert
       Internet addresses and Subnet masks to and from text

SYNOPSIS
       #include <libreswan.h>

       const char *ttoaddr(const char *src, size_t srclen,
	   int af, ip_address *addr);
       const char *tnatoaddr(const char *src, size_t srclen,
	   int af, ip_address *addr);
       size_t addrtot(const ip_address *addr, int format,
	   char *dst, size_t dstlen);

       const char *ttosubnet(const char *src, size_t srclen,
	   int af, ip_subnet *dst);
       size_t subnettot(const ip_subnet *sub, int format,
	   char *dst, size_t dstlen);

DESCRIPTION
       Ttoaddr converts a text-string name or numeric address into a binary address  (in  network
       byte  order).   Tnatoaddr does the same conversion, but the only text forms it accepts are
       the ``official'' forms of numeric address (dotted-decimal for IPv4, colon-hex  for  IPv6).
       Addrtot	does  the reverse conversion, from binary address back to a text form.	Ttosubnet
       and subnettot do likewise for the ``address/mask'' form used to write a specification of a
       subnet.

       An  IPv4  address  is  specified  in  text as a dotted-decimal address (e.g.  1.2.3.4), an
       eight-digit network-order hexadecimal number with the usual C  prefix  (e.g.   0x01020304,
       which  is synonymous with 1.2.3.4), an eight-digit host-order hexadecimal number with a 0h
       prefix (e.g.  0h01020304, which is synonymous  with  1.2.3.4  on  a  big-endian	host  and
       4.3.2.1	on  a little-endian host), a DNS name to be looked up via gethostbyname(3), or an
       old-style network name to be looked up via getnetbyname(3).

       A dotted-decimal address may  be  incomplete,  in  which  case  text-to-binary  conversion
       implicitly appends as many instances of .0 as necessary to bring it up to four components.
       The components of a dotted-decimal address are always taken as decimal, and leading  zeros
       are  ignored.  For example, 10 is synonymous with 10.0.0.0, and 128.009.000.032 is synony-
       mous with 128.9.0.32 (the latter example is verbatim from RFC 1166).  The result of apply-
       ing addrtot to an IPv4 address is always complete and does not contain leading zeros.

       Use  of hexadecimal addresses is strongly discouraged; they are included only to save has-
       sles when dealing with the handful of  perverted  programs  which  already  print  network
       addresses in hexadecimal.

       An    IPv6    address	is    specified   in   text   with   colon-hex	 notation   (e.g.
       0:56:78ab:22:33:44:55:66), colon-hex with :: abbreviating at most one subsequence of  mul-
       tiple  zeros (e.g.  99:ab::54:068, which is synonymous with 99:ab:0:0:0:0:54:68), or a DNS
       name to be looked up via gethostbyname(3).  The result of  applying  addrtot  to  an  IPv6
       address will use :: abbreviation if possible, and will not contain leading zeros.

       The letters in hexadecimal may be uppercase or lowercase or any mixture thereof.

       DNS  names  may	be  complete (optionally terminated with a ``.'')  or incomplete, and are
       looked up as specified by local system configuration (see resolver(5)).	The h_addr  value
       returned  by  gethostbyname2(3)	is  used, so with current DNS implementations, the result
       when the name corresponds to more than one address is difficult	to  predict.   IPv4  name
       lookup resorts to getnetbyname(3) only if gethostbyname2(3) fails.

       A  subnet specification is of the form network/mask.  The network and mask can be any form
       acceptable to ttoaddr.  In addition, and preferably, the mask can  be  a  decimal  integer
       (leading  zeros	ignored) giving a bit count, in which case it stands for a mask with that
       number of high bits on and all others off (e.g., 24 in IPv4 means 255.255.255.0).  In  any
       case,  the  mask must be contiguous (a sequence of high bits on and all remaining low bits
       off).  As a special case, the subnet specification %default is a synonym for 0.0.0.0/0  or
       ::/0 in IPv4 or IPv6 respectively.

       Ttosubnet ANDs the mask with the address before returning, so that any non-network bits in
       the address are turned off (e.g., 10.1.2.3/24 is synonymous with 10.1.2.0/24).	Subnettot
       always generates the decimal-integer-bit-count form of the mask, with no leading zeros.

       The  srclen  parameter  of  ttoaddr  and ttosubnet specifies the length of the text string
       pointed to by src; it is an error for there to be anything else (e.g., a terminating  NUL)
       within  that  length.  As a convenience for cases where an entire NUL-terminated string is
       to be converted, a srclen value of 0 is taken to mean strlen(src).

       The af parameter of ttoaddr and ttosubnet specifies the address family  of  interest.   It
       should be either AF_INET or AF_INET6.

       The  dstlen  parameter  of  addrtot and subnettot specifies the size of the dst parameter;
       under no circumstances are more than dstlen bytes written to dst.  A result which will not
       fit  is	truncated.  Dstlen can be zero, in which case dst need not be valid and no result
       is written, but the return value is unaffected; in all other cases,  the  (possibly  trun-
       cated)  result  is  NUL-terminated.   The libreswan.h header file defines constants, ADDR-
       TOT_BUF and SUBNETTOT_BUF, which are the sizes of buffers just large enough for worst-case
       results.

       The  format parameter of addrtot and subnettot specifies what format is to be used for the
       conversion.  The value 0 (not the character '0', but a zero value) specifies a  reasonable
       default,  and  is  in fact the only format currently available in subnettot.  Addrtot also
       accepts format values 'r' (signifying a text form suitable for DNS reverse  lookups,  e.g.
       4.3.2.1.IN-ADDR.ARPA.   for  IPv4  and  RFC  2874 format for IPv6), and 'R' (signifying an
       alternate reverse-lookup form, an error for IPv4 and RFC 1886 format for IPv6).	 Reverse-
       lookup names always end with a ``.''.

       The  text-to-binary  functions  return  NULL for success and a pointer to a string-literal
       error message for failure; see DIAGNOSTICS.  The binary-to-text functions return 0  for	a
       failure,  and otherwise always return the size of buffer which would be needed to accommo-
       date the full conversion result, including terminating NUL; it is the  caller's	responsi-
       bility  to check this against the size of the provided buffer to determine whether trunca-
       tion has occurred.

SEE ALSO
       inet(3)

DIAGNOSTICS
       Fatal errors in ttoaddr are: empty input; unknown address family; attempt to allocate tem-
       porary  storage	for  a very long name failed; name lookup failed; syntax error in dotted-
       decimal or colon-hex form; dotted-decimal or colon-hex component too large.

       Fatal errors in ttosubnet are: no / in src; ttoaddr error  in  conversion  of  network  or
       mask; bit-count mask too big; mask non-contiguous.

       Fatal errors in addrtot and subnettot are: unknown format.

HISTORY
       Written for the FreeS/WAN project by Henry Spencer.

BUGS
       The  interpretation of incomplete dotted-decimal addresses (e.g.  10/24 means 10.0.0.0/24)
       differs from that of some older conversion functions, e.g. those of inet(3).  The behavior
       of the older functions has never been particularly consistent or particularly useful.

       Ignoring  leading  zeros  in dotted-decimal components and bit counts is arguably the most
       useful behavior in this application, but it might occasionally cause  confusion	with  the
       historical use of leading zeros to denote octal numbers.

       Ttoaddr	does  not  support the mixed colon-hex-dotted-decimal convention used to embed an
       IPv4 address in an IPv6 address.

       Addrtot always uses the :: abbreviation (which can appear only once in an address) for the
       first  sequence	of  multiple  zeros  in  an  IPv6  address.   One can construct addresses
       (unlikely ones) in which this is suboptimal.

       Addrtot 'r' conversion of an IPv6 address uses lowercase hexadecimal,  not  the	uppercase
       used  in  RFC  2874's  examples.  It takes careful reading of RFCs 2874, 2673, and 2234 to
       realize that lowercase is technically legitimate here, and there  may  be  software  which
       botches this and hence would have trouble with lowercase hex.

       Possibly  subnettot  ought  to recognize the %default case and generate that string as its
       output.	Currently it doesn't.

       It is barely possible that somebody, somewhere, might have a legitimate use  for  non-con-
       tiguous subnet masks.

       Getnetbyname(3) is a historical dreg.

       Tnatoaddr probably should enforce completeness of dotted-decimal addresses.

       The  restriction of text-to-binary error reports to literal strings (so that callers don't
       need to worry about freeing them or copying  them)  does  limit	the  precision	of  error
       reporting.

       The  text-to-binary  error-reporting  convention  lends	itself	to slightly obscure code,
       because many readers will not think of NULL as signifying success.  A good way to make  it
       clearer is to write something like:

	      const char *error;

	      error = ttoaddr( /* ... */ );
	      if (error != NULL) {
		      /* something went wrong */

					   28 Sept 2001 			 IPSEC_TTOADDR(3)
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