NAME
inet6_rthdr_space,
inet6_rthdr_init,
inet6_rthdr_add,
inet6_rthdr_lasthop,
inet6_rthdr_reverse,
inet6_rthdr_segments,
inet6_rthdr_getaddr,
inet6_rthdr_getflags
—
IPv6 Routing Header Options manipulation
SYNOPSIS
#include <netinet/in.h>
size_t
inet6_rthdr_space(
int
type,
int segments);
struct cmsghdr *
inet6_rthdr_init(
void
*bp,
int type);
int
inet6_rthdr_add(
struct
cmsghdr *cmsg,
const struct
in6_addr *addr,
unsigned
int flags);
int
inet6_rthdr_lasthop(
struct
cmsghdr *cmsg,
unsigned int
flags);
int
inet6_rthdr_reverse(
const
struct cmsghdr *in,
struct
cmsghdr *out);
int
inet6_rthdr_segments(
const
struct cmsghdr *cmsg);
struct in6_addr *
inet6_rthdr_getaddr(
struct
cmsghdr *cmsg,
int
index);
int
inet6_rthdr_getflags(
const
struct cmsghdr *cmsg,
int
index);
DESCRIPTION
RFC 2292 IPv6 advanced API defines eight functions that the application calls to
build and examine a Routing header. Four functions build a Routing header:
- inet6_rthdr_space()
- return #bytes required for ancillary data
- inet6_rthdr_init()
- initialize ancillary data for Routing header
- inet6_rthdr_add()
- add IPv6 address & flags to Routing header
- inet6_rthdr_lasthop()
- specify the flags for the final hop
Four functions deal with a returned Routing header:
- inet6_rthdr_reverse()
- reverse a Routing header
- inet6_rthdr_segments()
- return #segments in a Routing header
- inet6_rthdr_getaddr()
- fetch one address from a Routing header
- inet6_rthdr_getflags()
- fetch one flag from a Routing header
The function prototypes for these functions are all in the
<netinet/in.h> header.
inet6_rthdr_space
This function returns the number of bytes required to hold a Routing header of
the specified
type containing the specified number of
segments (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.
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.
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
sendmsg(2) as a single
msg_control
buffer.
inet6_rthdr_init
This function initializes the buffer pointed to by
bp to
contain a
cmsghdr
structure followed by a Routing
header of the specified
type. The
cmsg_len
member of the
cmsghdr
structure is initialized to the size of the structure plus the amount of space
required by the Routing header. The
cmsg_level
and
cmsg_type
members are also initialized as required.
The caller must allocate the buffer and its size can be determined by calling
inet6_rthdr_space().
Upon success the return value is the pointer to the
cmsghdr
structure, and this is then used as the first
argument to the next two functions. Upon an error the return value is
NULL
.
inet6_rthdr_add
This function adds the address pointed to by
addr to the
end of the Routing header being constructed and sets the type of this hop to
the value of
flags. For an IPv6 Type 0 Routing header,
flags must be either
IPV6_RTHDR_LOOSE
or
IPV6_RTHDR_STRICT
.
If successful, the
cmsg_len
member of the
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.
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,
flags must be
either
IPV6_RTHDR_LOOSE
or
IPV6_RTHDR_STRICT
.
The return value of the function is 0 upon success, or -1 upon an error.
Notice that a Routing header specifying
N
intermediate
nodes requires
N+1
Strict/Loose flags. This requires
N
calls to
inet6_rthdr_add()
followed by one call to
inet6_rthdr_lasthop().
inet6_rthdr_reverse
This function takes a Routing header that was received as ancillary data
(pointed to by the first argument,
in) 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 (that is, the reversal can
occur in place).
The return value of the function is 0 on success, or -1 upon an error.
inet6_rthdr_segments
This function returns the number of segments (addresses) contained in the
Routing header described by
cmsg. On success the return
value is between 1 and 23, inclusive. The return value of the function is -1
upon an error.
inet6_rthdr_getaddr
This function returns a pointer to the IPv6 address specified by
index (which must have a value between 1 and the value
returned by
inet6_rthdr_segments()) in the Routing header
described by
cmsg. An application should first call
inet6_rthdr_segments() to obtain the number of segments in
the Routing header.
Upon an error the return value of the function is
NULL
.
inet6_rthdr_getflags
This function returns the flags value specified by
index
(which must have a value between 0 and the value returned by
inet6_rthdr_segments()) in the Routing header described by
cmsg. For an IPv6 Type 0 Routing header the return value
will be either
IPV6_RTHDR_LOOSE
or
IPV6_RTHDR_STRICT
.
Upon an error the return value of the function is -1.
Note: Addresses are indexed starting at 1, and flags starting at 0, to maintain
consistency with the terminology and figures in RFC 2460.
EXAMPLES
RFC 2292 gives comprehensive examples in chapter 8.
DIAGNOSTICS
inet6_rthdr_space() returns 0 on errors.
inet6_rthdr_add(),
inet6_rthdr_lasthop() and
inet6_rthdr_reverse() return 0 on success, and returns -1 on
error.
inet6_rthdr_init() and
inet6_rthdr_getaddr()
return
NULL
on error.
inet6_rthdr_segments() and
inet6_rthdr_getflags() return -1 on error.
SEE ALSO
W. Stevens and M.
Thomas, Advanced Sockets API for IPv6,
RFC 2292, February
1998.
S. Deering and R.
Hinden, Internet Protocol, Version 6 (IPv6)
Specification, RFC 2460,
December 1998.
STANDARDS
The functions are documented in “Advanced Sockets API for IPv6” (RFC
2292).
HISTORY
The implementation first appeared in KAME advanced networking kit.
BUGS
The text was shamelessly copied from RFC 2292.
inet6_rthdr_reverse() is not implemented yet.