inet6(4) BSD Kernel Interfaces Manual inet6(4)
NAME
inet6 -- Internet protocol version 6 family
SYNOPSIS
#include <sys/types.h>
#include <netinet/in.h>
DESCRIPTION
The inet6 family is an updated version of inet(4) family. While inet(4)
implements Internet Protocol version 4, inet6 implements Internet Proto-
col version 6.
inet6 is a collection of protocols layered atop the Internet Protocol
version 6 (IPv6) transport layer, and utilizing the IPv6 address format.
The inet6 family provides protocol support for the SOCK_STREAM,
SOCK_DGRAM, and SOCK_RAW socket types; the SOCK_RAW interface provides
access to the IPv6 protocol.
ADDRESSING
IPv6 addresses are 16 byte quantities, stored in network standard byte-
order. The include file <netinet/in.h> defines this address as a dis-
criminated union.
Sockets bound to the inet6 family utilize the following addressing struc-
ture:
struct sockaddr_in6 {
u_int8_t sin6_len;
u_int8_t sin6_family;
u_int16_t sin6_port;
u_int32_t sin6_flowinfo;
struct in6_addr sin6_addr;
u_int32_t sin6_scope_id;
};
Sockets may be created with the local address ``::'' (which is equal to
IPv6 address 0:0:0:0:0:0:0:0) to affect ``wildcard'' matching on incoming
messages.
The IPv6 specification defines scoped addresses, like link-local or site-
local addresses. A scoped address is ambiguous to the kernel, if it is
specified without a scope identifier. To manipulate scoped addresses
properly from the userland, programs must use the advanced API defined in
RFC2292. A compact description of the advanced API is available in
ip6(4). If a scoped address is specified without an explicit scope, the
kernel may raise an error. Note that scoped addresses are not for daily
use at this moment, both from a specification and an implementation point
of view.
The KAME implementation supports an extended numeric IPv6 address nota-
tion for link-local addresses, like ``fe80::1%de0'' to specify ``fe80::1
on de0 interface''. This notation is supported by getaddrinfo(3) and
getnameinfo(3). Some of normal userland programs, such as telnet(1) or
ftp(1), are able to use this notation. With special programs like
ping6(8), you can specify the outgoing interface by an extra command line
option to disambiguate scoped addresses.
Scoped addresses are handled specially in the kernel. In kernel struc-
tures like routing tables or interface structures, a scoped address will
have its interface index embedded into the address. Therefore, the
address in some kernel structures is not the same as that on the wire.
The embedded index will become visible through a PF_ROUTE socket, kernel
memory accesses via kvm(3) and on some other occasions. HOWEVER, users
should never use the embedded form. For details please consult
IMPLEMENTATION supplied with KAME kit.
PROTOCOLS
The inet6 family is comprised of the IPv6 network protocol, Internet Con-
trol Message Protocol version 6 (ICMPv6), Transmission Control Protocol
(TCP), and User Datagram Protocol (UDP). TCP is used to support the
SOCK_STREAM abstraction while UDP is used to support the SOCK_DGRAM
abstraction. Note that TCP and UDP are common to inet(4) and inet6. A
raw interface to IPv6 is available by creating an Internet socket of type
SOCK_RAW. The ICMPv6 message protocol is accessible from a raw socket.
MIB Variables
A number of variables are implemented in the net.inet6 branch of the
sysctl(3) MIB. In addition to the variables supported by the transport
protocols (for which the respective manual pages may be consulted), the
following general variables are defined:
IPV6CTL_FORWARDING (ip6.forwarding) Boolean: enable/disable forward-
ing of IPv6 packets. Also, identify if the node
is acting as a router. Defaults to off.
IPV6CTL_SENDREDIRECTS (ip6.redirect) Boolean: enable/disable sending of
ICMPv6 redirects in response to unforwardable
IPv6 packets. This option is ignored unless the
node is routing IPv6 packets, and should normally
be enabled on all systems. Defaults to on.
IPV6CTL_DEFHLIM (ip6.hlim) Integer: default hop limit value to
use for outgoing IPv6 packets. This value
applies to all the transport protocols on top of
IPv6. There are APIs to override the value.
IPV6CTL_MAXFRAGPACKETS (ip6.maxfragpackets) Integer: default maximum
number of fragmented packets the node will
accept. 0 means that the node will not accept
any fragmented packets. -1 means that the node
will accept as many fragmented packets as it
receives. The flag is provided basically for
avoiding possible DoS attacks.
IPV6CTL_ACCEPT_RTADV (ip6.accept_rtadv) Boolean: enable/disable
receiving of ICMPv6 router advertisement packets,
and autoconfiguration of address prefixes and
default routers. The node must be a host (not a
router) for the option to be meaningful.
Defaults to off.
IPV6CTL_LOG_INTERVAL (ip6.log_interval) Integer: default interval
between IPv6 packet forwarding engine log output
(in seconds).
IPV6CTL_HDRNESTLIMIT (ip6.hdrnestlimit) Integer: default number of the
maximum IPv6 extension headers permitted on
incoming IPv6 packets. If set to 0, the node
will accept as many extension headers as possi-
ble.
IPV6CTL_DAD_COUNT (ip6.dad_count) Integer: default number of IPv6
DAD (duplicated address detection) probe packets.
The packets will be generated when IPv6 interface
addresses are configured.
IPV6CTL_AUTO_FLOWLABEL (ip6.auto_flowlabel) Boolean: enable/disable
automatic filling of IPv6 flowlabel field, for
outstanding connected transport protocol packets.
The field might be used by intermediate routers
to identify packet flows. Defaults to on.
IPV6CTL_DEFMCASTHLIM (ip6.defmcasthlim) Integer: default hop limit
value for an IPv6 multicast packet sourced by the
node. This value applies to all the transport
protocols on top of IPv6. There are APIs to
override the value as documented in ip6(4).
IPV6CTL_GIF_HLIM (ip6.gifhlim) Integer: default maximum hop limit
value for an IPv6 packet generated by gif(4) tun-
nel interface.
IPV6CTL_KAME_VERSION (ip6.kame_version) String: identifies the version
of KAME IPv6 stack implemented in the kernel.
IPV6CTL_USE_DEPRECATED (ip6.use_deprecated) Boolean: enable/disable use
of deprecated address, specified in RFC2462
5.5.4. Defaults to on.
IPV6CTL_RR_PRUNE (ip6.rr_prune) Integer: default interval between
IPv6 router renumbering prefix babysitting, in
seconds.
IPV6CTL_MAPPED_ADDR (ip6.mapped_addr) Boolean: enable/disable use of
IPv4 mapped address on AF_INET6 sockets.
Defaults to on.
IPV6CTL_RTEXPIRE (ip6.rtexpire) Integer: lifetime in seconds of
protocol-cloned IP routes after the last refer-
ence drops (default one hour).
IPV6CTL_RTMINEXPIRE (ip6.rtminexpire) Integer: minimum value of
ip.rtexpire (default ten seconds).
IPV6CTL_RTMAXCACHE (ip6.rtmaxcache) Integer: trigger level of
cached, unreferenced, protocol-cloned routes
which initiates dynamic adaptation (default 128).
Interaction between IPv4/v6 sockets
The behavior of AF_INET6 TCP/UDP socket is documented in RFC2553. Basi-
cally, it says this:
o A specific bind on an AF_INET6 socket (bind(2) with an address speci-
fied) should accept IPv6 traffic to that address only.
o If you perform a wildcard bind on an AF_INET6 socket (bind(2) to IPv6
address ::), and there is no wildcard bind AF_INET socket on that
TCP/UDP port, IPv6 traffic as well as IPv4 traffic should be routed
to that AF_INET6 socket. IPv4 traffic should be seen as if it came
from an IPv6 address like ::ffff:10.1.1.1. This is called an IPv4
mapped address.
o If there are both a wildcard bind AF_INET socket and a wildcard bind
AF_INET6 socket on one TCP/UDP port, they should behave separately.
IPv4 traffic should be routed to the AF_INET socket and IPv6 should
be routed to the AF_INET6 socket.
However, RFC2553 does not define the ordering constraint between calls to
bind(2), nor how IPv4 TCP/UDP port numbers and IPv6 TCP/UDP port numbers
relate to each other (should they be integrated or separated). Imple-
mented behavior is very different from kernel to kernel. Therefore, it
is unwise to rely too much upon the behavior of AF_INET6 wildcard bind
sockets. It is recommended to listen to two sockets, one for AF_INET and
another for AF_INET6, when you would like to accept both IPv4 and IPv6
traffic.
It should also be noted that malicious parties can take advantage of the
complexity presented above, and are able to bypass access control, if the
target node routes IPv4 traffic to AF_INET6 socket. Users are advised to
take care handling connections from IPv4 mapped address to AF_INET6 sock-
ets.
SEE ALSO
ioctl(2), socket(2), sysctl(3), icmp6(4), intro(4), ip6(4), tcp(4),
ttcp(4), udp(4)
STANDARDS
Tatsuya Jinmei and Atsushi Onoe, An Extension of Format for IPv6 Scoped
Addresses, internet draft, draft-ietf-ipngwg-scopedaddr-format-02.txt,
June 2000, work in progress material.
HISTORY
The inet6 protocol interfaces are defined in RFC2553 and RFC2292. The
implementation described herein appeared in the WIDE/KAME project.
BUGS
The IPv6 support is subject to change as the Internet protocols develop.
Users should not depend on details of the current implementation, but
rather the services exported.
Users are suggested to implement ``version independent'' code as much as
possible, as you will need to support both inet(4) and inet6.
BSD January 29, 1999 BSD
Mac OS X 10.9 - Generated Wed Oct 16 06:04:11 CDT 2013