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
inet6_rthdr_space(int type, int segments);
struct cmsghdr *
inet6_rthdr_init(void *bp, int type);
inet6_rthdr_add(struct cmsghdr *cmsg, const struct in6_addr *addr,
unsigned int flags);
inet6_rthdr_lasthop(struct cmsghdr *cmsg, unsigned int flags);
inet6_rthdr_reverse(const struct cmsghdr *in, struct cmsghdr *out);
inet6_rthdr_segments(const struct cmsghdr *cmsg);
struct in6_addr *
inet6_rthdr_getaddr(struct cmsghdr *cmsg, int index);
inet6_rthdr_getflags(const struct cmsghdr *cmsg, int index);
RFC2292 IPv6 advanced API defines eight functions that the application
calls to build and examine a Routing header. Four functions build a
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>
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
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
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
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.
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.
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().
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
The return value of the function is 0 on success, or -1 upon an error.
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
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.
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 RFC2460.
RFC2292 gives comprehensive examples in chapter 8.
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.
W. Stevens and M. Thomas, Advanced Sockets API for IPv6, RFC2292,
S. Deering and R. Hinden, Internet Protocol, Version 6 (IPv6)
Specification, RFC2460, December 1998.
The functions are documented in ``Advanced Sockets API for IPv6''
The implementation first appeared in KAME advanced networking kit.
The text was shamelessly copied from RFC2292.
inet6_rthdr_reverse() is not implemented yet.
BSD December 10, 1999 BSD
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