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
Protocol 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 byteorder. The
include file
<netinet/in.h> defines
this address as a discriminated union.
Sockets bound to the
inet6 family utilize the following
addressing structure:
struct sockaddr_in6 {
uint8_t sin6_len;
sa_family_t sin6_family;
in_port_t sin6_port;
uint32_t sin6_flowinfo;
struct in6_addr sin6_addr;
uint32_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 notation 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 structures 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 Control 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 forwarding 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_KEEPFAITH
- (ip6.keepfaith) Boolean: enable/disable “FAITH”
TCP relay IPv6-to-IPv4 translator code in the kernel. Refer
faith(4) and faithd(8) for detail.
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 possible.
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) tunnel
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_V6ONLY
- (ip6.v6only) Boolean: enable/disable the prohibited 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 reference 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¶
By default,
FreeBSD does not route IPv4 traffic to
AF_INET6
sockets. The default behavior intentionally
violates RFC2553 for security reasons. Listen to two sockets if you want to
accept both IPv4 and IPv6 traffic. IPv4 traffic may be routed with certain
per-socket/per-node configuration, however, it is not recommended to do so.
Consult
ip6(4) for details.
The behavior of
AF_INET6
TCP/UDP socket is documented in
RFC2553. Basically, it says this:
- A specific bind on an
AF_INET6
socket (bind(2) with an
address specified) should accept IPv6 traffic to that address only.
- 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.
- 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).
Implemented 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
sockets.
SEE ALSO¶
ioctl(2),
socket(2),
sysctl(3),
icmp6(4),
intro(4),
ip6(4),
tcp(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.