INET6_RTHDR_SPACE(3)

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.

RETURN VALUES
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, M. Thomas, Advanced Sockets API for IPv6, RFC 2292, February 1998. S. Deering, 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.