inet6_rth, inet6_rth_space, inet6_rth_init, inet6_rth_add,
inet6_rth_reverse, inet6_rth_segments, inet6_rth_getaddr - Routing
cc [ flag ... ] file ... -lsocket [library]
socklen_t inet6_rth_space(int type, int segments);
void *inet6_rth_init(void *bp, socklen_t 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);
The inet6_rth functions enable users to manipulate routing headers
without having knowledge of their structure.
The iet6_rth_init() function initializes the buffer pointed to by bp to
contain a routing header of the specified type and sets ip6r_len based
on the segments parameter. The bp_len argument is used only to verify
that the buffer is large enough. The ip6r_segleft field is set to zero
and inet6_rth_add() increments it. The caller allocates the buffer and
its size can be determined by calling inet6_rth_space().
The inet6_rth_add() function adds the IPv6 address pointed to by addr
to the end of the routing header that is being constructed.
The inet6_rth_reverse() function takes a routing header extension
header pointed to by the first argument and writes a new routing header
that sends datagrams along the reverse of the 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 can point
to the same buffer (that is, the reversal can occur in place).
The inet6_rth_segments() function returns the number of segments
(addresses) contained in the routing header described by bp.
The inet6_rth_getaddr() function returns a pointer to the IPv6 address
specified by index, which must have a value between 0 and one less than
the value returned by inet6_rth_segments() in the routing header
described by bp. Applications should first call inet6_rth_segments() to
obtain the number of segments in the routing header.
The inet6_rth_space() function returns the size, but the function does
not allocate the space required for the ancillary data routing header.
To receive a routing header, the application must enable the
IPV6_RECVRTHDR socket option:
int on = 1;
setsockopt (fd, IPPROTO_IPV6, IPV6_RECVRTHDR, &on, sizeof(on));
Each received routing header is returned as one ancillary data object
described by a cmsghdr structure with cmsg_type set to IPV6_RTHDR.
To send a routing header, the application specifies it either as ancil‐
lary data in a call to sendmsg() or by using setsockopt(). For the
sending side, this API assumes the number of occurrences of the routing
header as described in RFC-2460. Applications can specify no more than
one outgoing routing header.
The application can remove any sticky routing header by calling set‐
sockopt() for IPV6_RTHDR with a zero option length.
When using ancillary data, a routing header is passed between the
application and the kernel as follows: The cmsg_level member has a
value of IPPROTO_IPV6 and the cmsg_type member has a value of
IPV6_RTHDR. The contents of the cmsg_data member is implementation-
dependent and should not be accessed directly by the application, but
should be accessed using the inet6_rth functions.
The following constant is defined as a result of including the
#define IPV6_RTHDR_TYPE_0 0 /* IPv6 Routing header type 0 */
ROUTING HEADER OPTION
Source routing in IPv6 is accomplished by specifying a routing header
as an extension header. There are a number of different routing head‐
ers, but IPv6 currently defines only the Type 0 header. See RFC-2460.
The Type 0 header supports up to 127 intermediate nodes, limited by the
length field in the extension header. With this maximum number of
intermediate nodes, a source, and a destination, there are 128 hops.
The inet6_rth_init() function returns a pointer to the buffer (bp) upon
For the inet6_rth_add() function, the segleft member of the routing
header is updated to account for the new address in the routing header.
The function returns 0 upon success and -1 upon failure.
The inet6_rth_reverse() function returns 0 upon success or -1 upon an
The inet6_rth_segments() function returns 0 or greater upon success and
-1 upon an error.
The inet6_rth_getaddr() function returns NULL upon an error.
The inet6_rth_space() function returns the size of the buffer needed
for the routing header.
See attributes(5) for descriptions of the following attributes:
│ ATTRIBUTE TYPE │ ATTRIBUTE VALUE │
│Interface Stability │ Standard │
│MT-Level │ Safe │
RFC 3542- Advanced Sockets Application Programming Interface (API) for
IPv6, The Internet Society. May 2003
Feb 15, 2007 INET6_RTH(3SOCKET)