ip6(7P)
NAME
ip6 - Internet Protocol Version 6
SYNOPSIS
#include <sys/socket.h>
#include <netinet/in.h>,
#include <netinet/ip6.h>
s = socket(AF_INET6, SOCK_RAW, proto);
t = t_open ("/dev/rawip6", O_RDWR);
DESCRIPTION
The IPv6 protocol is the next generation of the internetwork
datagram delivery protocol of the Internet protocol family.
Programs may use IPv6 through higher-level protocols such as
the Transmission Control Protocol (TCP) or the User Datagram
Protocol (UDP), or may interface directly to IPv6. See
tcp(7P) and udp(7P). Direct access may be by means of the
socket interface, using a "raw socket," or by means of the
Transport Level Interface (TLI). The protocol options and
IPv6 extension headers defined in the IPv6 specification may
be set in outgoing datagrams.
APPLICATION PROGRAMMING INTERFACE
The STREAMS driver /dev/rawip6 is the TLI transport provider
that provides raw access to IPv6.
Raw IPv6 sockets are connectionless and are normally used
with the sendto() and recvfrom() calls (see send(3SOCKET)
and recv(3SOCKET)), although the connect(3SOCKET) call may
also be used to fix the destination for future datagrams. In
this case, the read(2) or recv(3SOCKET) and write(2) or
send(3SOCKET) calls may be used. Ancillary data may also be
sent or received over raw IPv6 sockets using the
sendmsg(3SOCKET) and recvmsg(3SOCKET) system calls.
Unlike raw IP, IPv6 applications do not include a complete
IPv6 header when sending; there is no IPv6 analog to the IP
IP_HDRINCL socket option. IPv6 header values may be speci-
fied or received as ancillary data to a sendmsg(3SOCKET) or
recvmsg(3SOCKET) system call, or may be specified as
"sticky" options on a per-socket basis by using the
setsockopt(3SOCKET) system call. Such sticky options are
applied to all outbound packets unless overridden by ancil-
lary data. If any ancillary data is specified in a
sendmsg(3SOCKET) call, all sticky options not explicitly
overridden revert to default values for that datagram only;
the sticky options persist as set for subsequent datagrams.
Since sendmsg(3SOCKET) is not supported for SOCK_STREAM
upper level protocols such as TCP, ancillary data is
unsupported for TCP. Sticky options, however, are supported.
Since sendmsg(3SOCKET) is supported for SOCK_DGRAM upper
level protocols, both ancillary data and sticky options are
supported for UDP, ICMP6, and raw IPv6 sockets.
The socket options supported at the IPv6 level are:
IPV6_BOUND_IF
Limit reception transmission of packets to this inter-
face. Takes an integer as an argument; the integer is
the selected interace index.
IPV6_UNSPEC_SRC
Boolean. Allow/disallow sending with a zero source
address.
IPV6_UNICAST_HOPS
Default hop limit for unicast datagrams. This option
takes an integer as an argument. Its value becomes the
new default value for ip6_hops that IPv6 will use on
outgoing unicast datagrams sent from that socket. The
initial default is 60.
IPV6_CHECKSUM
Specify the integer offset in bytes into the user data
of the checksum location. Does not apply to the ICMP6
protocol. Note: checksums are required for all IPv6
datagrams; this is different from IP, in which
datagram checksums were optional. IPv6 will compute
the ULP checksum if the value in the checksum field is
zero.
IPV6_SEC_OPT
Enable or obtain IPsec security settings for this
socket. For more details on the protection services of
IPsec, see ipsec(7P).
The following options are boolean switches controlling the
reception of ancillary data:
IPV6_RECVPKTINFO
Enable/disable receipt of the index of the interface
the packet arrived on, and of the inbound packet's
destination address.
IPV6_RECVHOPLIMIT
Enable/disable receipt of the inbound packet's current
hoplimit.
IPV6_RECVHOPOPTS
Enable/disable receipt of the inbound packet's IPv6
hop-by-hop extension header.
IPV6_RECVDSTOPTS
Enable/disable receipt of the inbound packet's IPv6
destination options extension header.
IPV6_RECVRTHDR
Enable/disable receipt of the inbound packet's IPv6
routing header.
IPV6_RECVRTHDRDSTOPTS
Enable/disable receipt of the inbound packet's
intermediate-hops options extension header.
The following options may be set as sticky options with
setsockopt(3SOCKET) or as ancillary data to a
sendmsg(3SOCKET) system call:
IPV6_PKTINFO
Set the source address and/or interface out which the
packet(s) will be sent. Takes a struct ip6_pktinfo as
the parameter.
IPV6_HOPLIMIT
Set the initial hoplimit for outbound datagrams. Takes
an integer as the parameter. Note: This option sets
the hoplimit only for ancillary data or sticky options
and does not change the default hoplimit for the
socket; see IPV6_UNICAST_HOPS and IPV6_MULTICAST_HOPS
to change the socket's default hoplimit.
IPV6_NEXTHOP
Specify the IPv6 address of the first hop, which must
be a neighbor of the sending host. Takes a struct
sockaddr_in6 as the parameter. When this option speci-
fies the same address as the destination IPv6 address
of the datagram, this is equivalent to the existing
SO_DONTROUTE option.
IPV6_HOPOPTS
Specify one or more hop-by-hop options. Variable
length. Takes a complete IPv6 hop-by-hop options
extension header as the parameter.
IPV6_DSTOPTS
Specify one or more destination options. Variable
length. Takes a complete IPv6 destination options
extension header as the parameter.
IPV6_RTHDR
Specify the IPv6 routing header. Variable length.
Takes a complete IPv6 routing header as the parameter.
Currently, only type 0 routing headers are supported.
IPV6_RTHDRDSTOPTS
Specify one or more destination options for all inter-
mediate hops. May be configured, but will not be
applied unless an IPv6 routing header is also config-
ured. Variable length. Takes a complete IPv6 destina-
tion options extension header as the parameter.
The following options affect the socket's multicast
behavior:
IPV6_JOIN_GROUP
Join a multicast group. Takes a struct ipv6_mreq as
the parameter; the structure contains a multicast
address and an interface index.
IPV6_LEAVE_GROUP
Leave a multicast group. Takes a struct ipv6_mreq as
the parameter; the structure contains a multicast
address and an interface index.
IPV6_MULTICAST_IF
The outgoing interface for multicast packets. This
option takes an integer as an argument; the integer is
the interface index of the selected interface.
IPV6_MULTICAST_HOPS
Default hop limit for multicast datagrams. This option
takes an integer as an argument. Its value becomes the
new default value for ip6_hops that IPv6 will use on
outgoing multicast datagrams sent from that socket.
The initial default is 1.
IPV6_MULTICAST_LOOP
Loopback for multicast datagrams. Normally multicast
datagrams are delivered to members on the sending
host. Setting the unsigned character argument to 0
will cause the opposite behavior.
The multicast socket options can be used with any datagram
socket type in the IPv6 family.
At the socket level, the socket option SO_DONTROUTE may be
applied. This option forces datagrams being sent to bypass
routing and forwarding by forcing the IPv6 hoplimit field to
1, meaning that the packet will not be forwarded by routers.
Raw IPv6 datagrams can also be sent and received using the
TLI connectionless primitives.
Datagrams flow through the IPv6 layer in two directions:
from the network up to user processes and from user
processes down to the network. Using this orientation, IPv6
is layered above the network interface drivers and below the
transport protocols such as UDP and TCP. The Internet Con-
trol Message Protocol (ICMPv6) for the Internet Protocol
Version 6 (IPv6) is logically a part of IPv6. See icmp6(7P).
Unlike IP, IPv6 provides no checksum of the IPv6 header.
Also unlike IP, upper level protocol checksums are required.
IPv6 will compute the ULP/data portion checksum if the
checksum field contains a zero (see IPV6_CHECKSUM option
above).
IPv6 extension headers in received datagrams are processed
in the IPv6 layer according to the protocol specification.
Currently recognized IPv6 extension headers include hop-by-
hop options header, destination options header, routing
header (currently, only type 0 routing headers are sup-
ported), and fragment header.
The IPv6 layer will normally act as a router (forwarding
datagrams that are not addressed to it, among other things)
when the machine has two or more IPv6 interfaces that are
up. This behavior can be overridden by using ndd(1M) to set
the /dev/ip6 variable, ip6_forwarding. The value 0 means do
not forward; the value 1 means forward. The initialization
scripts (see /etc/init.d/inetinit) set this value at boot
time based on the number of "up" interfaces and whether or
not the neighbor discovery protocol daemon configuration
file /etc/inet/ndpd.conf exists. The default value is zero;
ip6_forwarding is set to 1 only if more than one interface
has been configured for IPv6 and if /etc/inet/ndpd.conf
exists.
Additionally, finer grained forwarding can be configured in
IPv6. Each interface will create an ifname:ip6_forwarding
/dev/ip6 variable that can be modified using ndd(1M). If a
per-interface :ip6_forwarding variable is set to 0, packets
will neither be forwarded from this interface to others, nor
forwarded to this interface. Setting the ip6_forwarding
variable will toggle all of the per-interface
:ip6_forwarding variables to the setting of ip6_forwarding.
The IPv6 layer will send an ICMP6 message back to the source
host in many cases when it receives a datagram that can not
be handled. A "time exceeded" ICMP6 message will be sent if
the ip6_hops field in the IPv6 header drops to zero in the
process of forwarding a datagram. A "destination unreach-
able" message will be sent by a router or by the originating
host if a datagram can not be sent on because there is no
route to the final destination; it will be sent by a router
when it encounters a firewall prohibition; it will be sent
by a destination node when the transport protocol (that is,
TCP) has no listener. A "packet too big" message will be
sent by a router if the packet is larger than the MTU of the
outgoing link (this is used for Path MTU Discovery). A
"parameter problem" message will be sent if there is a prob-
lem with a field in the IPv6 header or any of the IPv6
extension headers such that the packet cannot be fully pro-
cessed.
The IPv6 layer supports fragmentation and reassembly.
Datagrams are fragmented on output if the datagram is larger
than the maximum transmission unit (MTU) of the network
interface. Fragments of received datagrams are dropped from
the reassembly queues if the complete datagram is not recon-
structed within a short time period.
Errors in sending discovered at the network interface driver
layer are passed by IPv6 back up to the user process.
SEE ALSO
ndd(1M), read(2), write(2), bind(3SOCKET), connect(3SOCKET),
getsockopt(3SOCKET), recv(3SOCKET), recvmsg(3SOCKET),
send(3SOCKET), sendmsg(3SOCKET), setsockopt(3SOCKET),
defaultrouter(4), icmp6(7P), if_tcp(7P), ipsec(7P),
inet6(7P), routing(7P), tcp(7P), udp(7P)
Deering, S. and Hinden, B. RFC 2460, Internet Protocol,
Version 6 (IPv6) Specification. The Internet Society.
December, 1998.
Stevens, W., and Thomas, M. RFC 2292, Advanced Sockets API
for IPv6. Network Working Group. February 1998.
DIAGNOSTICS
A socket operation may fail with one of the following errors
returned:
EACCES
A bind() operation was attempted with a "reserved"
port number and the effective user ID of the process
was not the privileged user.
EADDRINUSE
A bind() operation was attempted on a socket with a
network address/port pair that has already been bound
to another socket.
EADDRNOTAVAIL
A bind() operation was attempted for an address that
is not configured on this machine.
EINVAL
A sendmsg() operation with a non-NULL msg_accrights
was attempted.
EINVAL
A getsockopt() or setsockopt() operation with an
unknown socket option name was given.
EINVAL
A getsockopt() or setsockopt() operation was attempted
with the IPv6 option field improperly formed; an
option field was shorter than the minimum value or
longer than the option buffer provided; the value in
the option field was invalid.
EISCONN
A connect() operation was attempted on a socket on
which a connect() operation had already been per-
formed, and the socket could not be successfully
disconnected before making the new connection.
EISCONN
A sendto() or sendmsg() operation specifying an
address to which the message should be sent was
attempted on a socket on which a connect() operation
had already been performed.
EMSGSIZE
A send(), sendto(), or sendmsg() operation was
attempted to send a datagram that was too large for an
interface, but was not allowed to be fragmented (such
as broadcasts).
ENETUNREACH
An attempt was made to establish a connection via con-
nect(), or to send a datagram by means of sendto() or
sendmsg(), where there was no matching entry in the
routing table; or if an ICMP "destination unreachable"
message was received.
ENOTCONN
A send() or write() operation, or a sendto() or
sendmsg() operation not specifying an address to which
the message should be sent, was attempted on a socket
on which a connect() operation had not already been
performed.
ENOBUFS
The system ran out of memory for fragmentation buffers
or other internal data structures.
ENOMEM
The system was unable to allocate memory for an IPv6
socket option or other internal data structures.
ENOPROTOOPT
An IP socket option was attempted on an IPv6 socket,
or an IPv6 socket option was attempted on an IP
socket.
NOTES
Applications using the sockets API must use the Advanced
Sockets API for IPv6 (RFC 2292) to see elements of the
inbound packet's IPv6 header or extension headers.
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