INET6_RTHDR_SPACE(3) BSD Library Functions Manual INET6_RTHDR_SPACE(3)
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
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);
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.
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 ancil-
lary 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.
This function initializes the buffer pointed to by bp to contain a cmsghdr structure fol-
lowed by a Routing header of the specified type. The cmsg_len member of the cmsghdr struc-
ture 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
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
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.
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.
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
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.
RFC 2292 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, RFC 2292, February 1998.
S. Deering and R. Hinden, Internet Protocol, Version 6 (IPv6) Specification, RFC 2460,
The functions are documented in ``Advanced Sockets API for IPv6'' (RFC 2292).
The implementation first appeared in KAME advanced networking kit.
The text was shamelessly copied from RFC 2292.
inet6_rthdr_reverse() is not implemented yet.
BSD December 10, 1999 BSD