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+.TH IPSEC_INITSUBNET 3 "12 March 2002"
+.\" RCSID $Id: initsubnet.3,v 1.1 2004/03/15 20:35:26 as Exp $
+.SH NAME
+ipsec initsubnet \- initialize an ip_subnet
+.br
+ipsec addrtosubnet \- initialize a singleton ip_subnet
+.br
+ipsec subnettypeof \- get address type of an ip_subnet
+.br
+ipsec masktocount \- convert subnet mask to bit count
+.br
+ipsec networkof \- get base address of an ip_subnet
+.br
+ipsec maskof \- get subnet mask of an ip_subnet
+.SH SYNOPSIS
+.B "#include <freeswan.h>"
+.sp
+.B "const char *initsubnet(const ip_address *addr,"
+.ti +1c
+.B "int maskbits, int clash, ip_subnet *dst);"
+.br
+.B "const char *addrtosubnet(const ip_address *addr,"
+.ti +1c
+.B "ip_subnet *dst);"
+.sp
+.B "int subnettypeof(const ip_subnet *src);"
+.br
+.B "int masktocount(const ip_address *src);"
+.br
+.B "void networkof(const ip_subnet *src, ip_address *dst);"
+.br
+.B "void maskof(const ip_subnet *src, ip_address *dst);"
+.SH DESCRIPTION
+The
+.B <freeswan.h>
+library uses an internal type
+.I ip_subnet
+to contain a description of an IP subnet
+(base address plus mask).
+These functions provide basic tools for creating and examining this type.
+.PP
+.I Initsubnet
+initializes a variable
+.I *dst
+of type
+.I ip_subnet
+from a base address and
+a count of mask bits.
+The
+.I clash
+parameter specifies what to do if the base address includes
+.B 1
+bits outside the prefix specified by the mask
+(that is, in the ``host number'' part of the address):
+.RS
+.IP '0' 5
+zero out host-number bits
+.IP 'x'
+non-zero host-number bits are an error
+.RE
+.PP
+.I Initsubnet
+returns
+.B NULL
+for success and
+a pointer to a string-literal error message for failure;
+see DIAGNOSTICS.
+.PP
+.I Addrtosubnet
+initializes an
+.I ip_subnet
+variable
+.I *dst
+to a ``singleton subnet'' containing the single address
+.IR *addr .
+It returns
+.B NULL
+for success and
+a pointer to a string-literal error message for failure.
+.PP
+.I Subnettypeof
+returns the address type of a subnet,
+normally
+.B AF_INET
+or
+.BR AF_INET6 .
+(The
+.B <freeswan.h>
+header file arranges to include the necessary headers for these
+names to be known.)
+.PP
+.I Masktocount
+converts a subnet mask, expressed as an address, to a bit count
+suitable for use with
+.IR initsubnet .
+It returns
+.B \-1
+for error; see DIAGNOSTICS.
+.PP
+.I Networkof
+fills in
+.I *dst
+with the base address of subnet
+.IR src .
+.PP
+.I Maskof
+fills in
+.I *dst
+with the subnet mask of subnet
+.IR src ,
+expressed as an address.
+.SH SEE ALSO
+inet(3), ipsec_ttosubnet(3), ipsec_rangetosubnet(3)
+.SH DIAGNOSTICS
+Fatal errors in
+.I initsubnet
+are:
+unknown address family;
+unknown
+.I clash
+value;
+impossible mask bit count;
+non-zero host-number bits and
+.I clash
+is
+.BR 'x' .
+Fatal errors in
+.I addrtosubnet
+are:
+unknown address family.
+Fatal errors in
+.I masktocount
+are:
+unknown address family;
+mask bits not contiguous.
+.SH HISTORY
+Written for the FreeS/WAN project by Henry Spencer.