inet6_rth_add(), inet6_rth_getaddr(), inet6_rth_init(), inet6_rth_reverse(), inet6_rth_segments(), inet6_rth_space() — IPv6 Routing header options manipulation functions.
size_t inet6_rth_space(int type, int segments);
void *inet6_rth_init(void *bp, int bp_len, int type, int segments);
int inet6_rth_add(void *bp, const struct in6_addr *addr);
int inet6_rth_reverse(const void *in, void *out);
int inet6_rth_segments(const void *bp);
struct in6_addr *inet6_rth_getaddr(const void *bp, int index);
These functions can be used by an application to build
and examine an IPv6 Routing header. The Routing header can be used by an
IPv6 source to list one or more intermediate nodes to be visited on the
way to a packet's destination.
These three functions build a Routing header:
returns the number of bytes required for a Routing header.
initializes the buffer data for a Routing header.
adds one IPv6 address to the Routing header.
Three functions deal with a returned Routing header:
reverses a Routing header.
returns the number of segments in a Routing header.
fetches one address from a Routing header.
To receive a Routing header the application must enable the
int on = 1;
setsockopt(fd, IPPROTO_IPV6, IPV6_RECVRTHDR, &on, sizeof(on));
To send a Routing header the application specifies it either as ancillary data
in a call to
This function returns the number of bytes required to hold a routing
header of the specified
containing the specified number of
(addresses). For an IPv6 Type 0 Routing header, the number
of segments must be between 0 and 127, inclusive. The return value
is just the space for the Routing header. When the application uses
ancillary data, it must pass the returned length to
to determine how much memory is needed for the ancillary data object
(including the cmsghdr structure).
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.
This function returns the size but does not allocate the space
required for the ancillary data.
This function initializes the buffer pointed to by
to contain a
Routing header of the specified
is only used to verify if the buffer is
The caller must allocate the buffer, and its size can be determined by
Upon success, the return value is the pointer to the buffer
the pointer is then used as the first argument to the
function. Upon an error, the return value is NULL.
This function adds the IPv6 address pointed to by
to the end of
the Routing header being constructed.
If successful, the segleft member of the Routing header 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 takes a Routing header extension header pointed to by
the first argument
and writes a new Routing header.
The new Routing header sends
datagrams along the reverse of that route. The function reverses the
order of the addresses and sets the segleft member in the new routing
header to the number of segments. 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
This function returns the number of segments (addresses) contained in
the Routing header described by
which can be 0 or greater.
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 be a value between 0 and one less than the value
in the Routing header described by
An application should first call
the number of segments in the Routing header.
Upon an error, the return value of the function is NULL.
To use these functions, the application must be compiled
The APIs are implemented based on internet-draft
Advanced Sockets API for IPv6
The APIs may be updated, replaced, or obsoleted based on future changes
to the document.
Advanced Sockets API for IPv6
gives a comprehensive example in Appendix B.
The APIs were developed by HP.