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.\"     $OpenBSD: inet6_rthdr_space.3,v 1.8 2001/06/23 05:57:04 deraadt Exp $

.\"     $KAME: inet6_rthdr_space.3,v 1.8 2000/05/17 14:30:15 itojun Exp $

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.Dd December 10, 1999

.Dt INET6_RTHDR_SPACE 3

.Os

.\"

.Sh NAME

.Nm inet6_rthdr_space ,

.Nm inet6_rthdr_init ,

.Nm inet6_rthdr_add ,

.Nm inet6_rthdr_lasthop ,

.Nm inet6_rthdr_reverse ,

.Nm inet6_rthdr_segments ,

.Nm inet6_rthdr_getaddr ,

.Nm inet6_rthdr_getflags

.Nd IPv6 Routing Header Options manipulation

.\"

.Sh SYNOPSIS

.Fd #include 

.Ft size_t

.Fn inet6_rthdr_space "int type" "int segments"

.Ft "struct cmsghdr *"

.Fn inet6_rthdr_init "void *bp" "int type"

.Ft int

.Fn inet6_rthdr_add "struct cmsghdr *cmsg" "const struct in6_addr *addr" "unsigned int flags"

.Ft int

.Fn inet6_rthdr_lasthop "struct cmsghdr *cmsg" "unsigned int flags"

.Ft int

.Fn inet6_rthdr_reverse "const struct cmsghdr *in" "struct cmsghdr *out"

.Ft int

.Fn inet6_rthdr_segments "const struct cmsghdr *cmsg"

.Ft "struct in6_addr *"

.Fn inet6_rthdr_getaddr "struct cmsghdr *cmsg" "int index"

.Ft int

.Fn inet6_rthdr_getflags "const struct cmsghdr *cmsg" "int index"

.\"

.Sh DESCRIPTION

RFC2292 IPv6 advanced API defines eight

functions that the application calls to build and examine a Routing

header.

Four functions build a Routing header:

.Bl -hang

.It Fn inet6_rthdr_space

return #bytes required for ancillary data

.It Fn inet6_rthdr_init

initialize ancillary data for Routing header

.It Fn inet6_rthdr_add

add IPv6 address & flags to Routing header

.It Fn inet6_rthdr_lasthop

specify the flags for the final hop

.El

.Pp

Four functions deal with a returned Routing header:

.Bl -hang

.It Fn inet6_rthdr_reverse

reverse a Routing header

.It Fn inet6_rthdr_segments

return #segments in a Routing header

.It Fn inet6_rthdr_getaddr

fetch one address from a Routing header

.It Fn inet6_rthdr_getflags

fetch one flag from a Routing header

.El

.Pp

The function prototypes for these functions are all in the

.Aq Li netinet/in.h

header.

.\"

.Ss inet6_rthdr_space

This function returns the number of bytes required to hold a Routing

header of the specified

.Fa type

containing the specified number of

.Fa segments

.Pq addresses .

For an IPv6 Type 0 Routing header, the number

of segments must be between 1 and 23, inclusive.

The return value

includes the size of the cmsghdr structure that precedes the Routing

header, and any required padding.

.Pp

If the return value is 0, then either the type of the Routing header

is not supported by this implementation or the number of segments is

invalid for this type of Routing header.

.Pp

Note: This function returns the size but does not allocate the space

required for the ancillary data.

This allows an application to

allocate a larger buffer, if other ancillary data objects are

desired, since all the ancillary data objects must be specified to

.Xr sendmsg 2

as a single

.Li msg_control

buffer.

.\"

.Ss inet6_rthdr_init

This function initializes the buffer pointed to by

.Fa bp

to contain a

.Li cmsghdr

structure followed by a Routing header of the specified

.Fa type .

The

.Li cmsg_len

member of the

.Li cmsghdr

structure is initialized to the

size of the structure plus the amount of space required by the

Routing header.

The

.Li cmsg_level

and

.Li cmsg_type

members are also initialized as required.

.Pp

The caller must allocate the buffer and its size can be determined by

calling

.Fn inet6_rthdr_space .

.Pp

Upon success the return value is the pointer to the

.Li cmsghdr

structure, and this is then used as the first argument to the next

two functions.

Upon an error the return value is

.Dv NULL .

.\"

.Ss inet6_rthdr_add

This function adds the address pointed to by

.Fa addr

to the end of the

Routing header being constructed and sets the type of this hop to the

value of

.Fa flags .

For an IPv6 Type 0 Routing header,

.Fa flags

must be

either

.Dv IPV6_RTHDR_LOOSE

or

.Dv IPV6_RTHDR_STRICT .

.Pp

If successful, the

.Li cmsg_len

member of the

.Li cmsghdr

structure is

updated to account for the new address in the Routing header and the

return value of the function is 0.

Upon an error the return value of

the function is -1.

.\"

.Ss inet6_rthdr_lasthop

This function specifies the Strict/Loose flag for the final hop of a

Routing header.

For an IPv6 Type 0 Routing header,

.Fa flags

must be either

.Dv IPV6_RTHDR_LOOSE

or

.Dv IPV6_RTHDR_STRICT .

.Pp

The return value of the function is 0 upon success, or -1 upon an error.

.Pp

Notice that a Routing header specifying

.Li N

intermediate nodes requires

.Li N+1

Strict/Loose flags.

This requires

.Li N

calls to

.Fn inet6_rthdr_add

followed by one call to

.Fn inet6_rthdr_lasthop .

.\"

.Ss inet6_rthdr_reverse

This function takes a Routing header that was received as ancillary

data

.Po

pointed to by the first argument,

.Fa in

.Pc

and writes a new Routing

header that sends datagrams along the reverse of that route.

Both

arguments are allowed to point to the same buffer

.Pq that is, the reversal can occur in place .

.Pp

The return value of the function is 0 on success, or -1 upon an

error.

.\"

.Ss inet6_rthdr_segments

This function returns the number of segments

.Pq addresses

contained in

the Routing header described by

.Fa cmsg .

On success the return value is

between 1 and 23, inclusive.

The return value of the function is -1 upon an error.

.\"

.Ss inet6_rthdr_getaddr

This function returns a pointer to the IPv6 address specified by

.Fa index

.Po

which must have a value between 1 and the value returned by

.Fn inet6_rthdr_segments

.Pc

in the Routing header described by

.Fa cmsg .

An

application should first call

.Fn inet6_rthdr_segments

to obtain the number of segments in the Routing header.

.Pp

Upon an error the return value of the function is

.Dv NULL .

.\"

.Ss inet6_rthdr_getflags

This function returns the flags value specified by

.Fa index

.Po

which must

have a value between 0 and the value returned by

.Fn inet6_rthdr_segments

.Pc

in the Routing header described by

.Fa cmsg .

For an IPv6 Type 0 Routing header the return value will be either

.Dv IPV6_RTHDR_LOOSE

or

.Dv IPV6_RTHDR_STRICT .

.Pp

Upon an error the return value of the function is -1.

.Pp

Note: Addresses are indexed starting at 1, and flags starting at 0,

to maintain consistency with the terminology and figures in RFC2460.

.\"

.Sh DIAGNOSTICS

.Fn inet6_rthdr_space

returns 0 on errors.

.Pp

.Fn inet6_rthdr_add ,

.Fn inet6_rthdr_lasthop

and

.Fn inet6_rthdr_reverse

return 0 on success, and returns -1 on error.

.Pp

.Fn inet6_rthdr_init

and

.Fn inet6_rthdr_getaddr

return

.Dv NULL

on error.

.Pp

.Fn inet6_rthdr_segments

and

.Fn inet6_rthdr_getflags

return -1 on error.

.\"

.Sh EXAMPLES

RFC2292 gives comprehensive examples in chapter 8.

.\"

.Sh SEE ALSO

.Rs

.%A W. Stevens

.%A M. Thomas

.%T "Advanced Sockets API for IPv6"

.%N RFC2292

.%D February 1998

.Re

.Rs

.%A S. Deering

.%A R. Hinden

.%T "Internet Protocol, Version 6 (IPv6) Specification"

.%N RFC2460

.%D December 1998

.Re

.\"

.Sh HISTORY

The implementation first appeared in KAME advanced networking kit.

.\"

.Sh STANDARDS

The functions

are documented in

.Dq Advanced Sockets API for IPv6

.Pq RFC2292 .

.\"

.Sh BUGS

The text was shamelessly copied from RFC2292.

.Pp

.Fn inet6_rthdr_reverse

is not implemented yet.