INET6_RTHDR_SPACE(3) | Library Functions Manual | 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.

# 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.

December 10, 1999 | NetBSD 9.2