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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 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 {
                   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 with-out without
     out 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.  There-fore, Therefore,
     fore, 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 sup-port support
     port 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 con-sulted), consulted),
     sulted), 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 rout-ing routing
                             ing 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 pack-ets. packets.
                             ets.  -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 adver-tisement advertisement
                             tisement packets, and autoconfiguration of address prefixes and default
                             routers.  The node must be a host (not a router) for the option to be meaning-ful. meaningful.
                             ful.  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 head-ers headers
                             ers 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 flowla-bel flowlabel
                             bel 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 gen-erated generated
                             erated by gif(4) tunnel interface.

     IPV6CTL_KAME_VERSION    (ip6.kame_version) String: identifies the version of KAME IPv6 stack imple-mented implemented
                             mented in the kernel.

     IPV6CTL_USE_DEPRECATED  (ip6.use_deprecated) Boolean: enable/disable use of deprecated address, speci-fied specified
                             fied 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 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 protocolcloned
                             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.  Basically, it says this:
     •   A specific bind on an AF_INET6 socket (bind(2) with an address specified) should accept IPv6 traf-fic traffic
         fic 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 sepa-rated). separated).
     rated).  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 sock-ets, sockets,
     ets, one for AF_INET and another for AF_INET6, when you would like to accept both IPv4 and IPv6 traf-fic. traffic.
     fic.

     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), 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