rfc3513.txt

bind 9.3结合mysql数据库

   IPv6 nodes may have considerable or little knowledge of the internal
   structure of the IPv6 address, depending on the role the node plays
   (for instance, host versus router).  At a minimum, a node may
   consider that unicast addresses (including its own) have no internal
   structure:

   |                           128 bits                              |
   +-----------------------------------------------------------------+
   |                          node address                           |
   +-----------------------------------------------------------------+

   A slightly sophisticated host (but still rather simple) may
   additionally be aware of subnet prefix(es) for the link(s) it is
   attached to, where different addresses may have different values for
   n:

   |                         n bits                 |   128-n bits   |
   +------------------------------------------------+----------------+
   |                   subnet prefix                | interface ID   |
   +------------------------------------------------+----------------+

   Though a very simple router may have no knowledge of the internal
   structure of IPv6 unicast addresses, routers will more generally have
   knowledge of one or more of the hierarchical boundaries for the
   operation of routing protocols.  The known boundaries will differ



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   from router to router, depending on what positions the router holds
   in the routing hierarchy.

2.5.1 Interface Identifiers

   Interface identifiers in IPv6 unicast addresses are used to identify
   interfaces on a link.  They are required to be unique within a subnet
   prefix.  It is recommended that the same interface identifier not be
   assigned to different nodes on a link.  They may also be unique over
   a broader scope.  In some cases an interface's identifier will be
   derived directly from that interface's link-layer address.  The same
   interface identifier may be used on multiple interfaces on a single
   node, as long as they are attached to different subnets.

   Note that the uniqueness of interface identifiers is independent of
   the uniqueness of IPv6 addresses.  For example, a global unicast
   address may be created with a non-global scope interface identifier
   and a site-local address may be created with a global scope interface
   identifier.

   For all unicast addresses, except those that start with binary value
   000, Interface IDs are required to be 64 bits long and to be
   constructed in Modified EUI-64 format.

   Modified EUI-64 format based Interface identifiers may have global
   scope when derived from a global token (e.g., IEEE 802 48-bit MAC or
   IEEE EUI-64 identifiers [EUI64]) or may have local scope where a
   global token is not available (e.g., serial links, tunnel end-points,
   etc.) or where global tokens are undesirable (e.g., temporary tokens
   for privacy [PRIV]).

   Modified EUI-64 format interface identifiers are formed by inverting
   the "u" bit (universal/local bit in IEEE EUI-64 terminology) when
   forming the interface identifier from IEEE EUI-64 identifiers.  In
   the resulting Modified EUI-64 format the "u" bit is set to one (1) to
   indicate global scope, and it is set to zero (0) to indicate local
   scope.  The first three octets in binary of an IEEE EUI-64 identifier
   are as follows:

       0       0 0       1 1       2
      |0       7 8       5 6       3|
      +----+----+----+----+----+----+
      |cccc|ccug|cccc|cccc|cccc|cccc|
      +----+----+----+----+----+----+

   written in Internet standard bit-order , where "u" is the
   universal/local bit, "g" is the individual/group bit, and "c" are the
   bits of the company_id.  Appendix A: "Creating Modified EUI-64 format



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   Interface Identifiers" provides examples on the creation of Modified
   EUI-64 format based interface identifiers.

   The motivation for inverting the "u" bit when forming an interface
   identifier is to make it easy for system administrators to hand
   configure non-global identifiers when hardware tokens are not
   available.  This is expected to be case for serial links, tunnel end-
   points, etc.  The alternative would have been for these to be of the
   form 0200:0:0:1, 0200:0:0:2, etc., instead of the much simpler 1, 2,
   etc.

   The use of the universal/local bit in the Modified EUI-64 format
   identifier is to allow development of future technology that can take
   advantage of interface identifiers with global scope.

   The details of forming interface identifiers are defined in the
   appropriate "IPv6 over <link>" specification such as "IPv6 over
   Ethernet" [ETHER], "IPv6 over FDDI" [FDDI], etc.

2.5.2 The Unspecified Address

   The address 0:0:0:0:0:0:0:0 is called the unspecified address.  It
   must never be assigned to any node.  It indicates the absence of an
   address.  One example of its use is in the Source Address field of
   any IPv6 packets sent by an initializing host before it has learned
   its own address.

   The unspecified address must not be used as the destination address
   of IPv6 packets or in IPv6 Routing Headers.  An IPv6 packet with a
   source address of unspecified must never be forwarded by an IPv6
   router.

2.5.3 The Loopback Address

   The unicast address 0:0:0:0:0:0:0:1 is called the loopback address.
   It may be used by a node to send an IPv6 packet to itself.  It may
   never be assigned to any physical interface.   It is treated as
   having link-local scope, and may be thought of as the link-local
   unicast address of a virtual interface (typically called "the
   loopback interface") to an imaginary link that goes nowhere.

   The loopback address must not be used as the source address in IPv6
   packets that are sent outside of a single node.  An IPv6 packet with
   a destination address of loopback must never be sent outside of a
   single node and must never be forwarded by an IPv6 router.  A packet
   received on an interface with destination address of loopback must be
   dropped.




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2.5.4 Global Unicast Addresses

   The general format for IPv6 global unicast addresses is as follows:

   |         n bits         |   m bits  |       128-n-m bits         |
   +------------------------+-----------+----------------------------+
   | global routing prefix  | subnet ID |       interface ID         |
   +------------------------+-----------+----------------------------+

   where the global routing prefix is a (typically hierarchically-
   structured) value assigned to a site (a cluster of subnets/links),
   the subnet ID is an identifier of a link within the site, and the
   interface ID is as defined in section 2.5.1.

   All global unicast addresses other than those that start with binary
   000 have a 64-bit interface ID field (i.e., n + m = 64), formatted as
   described in section 2.5.1.  Global unicast addresses that start with
   binary 000 have no such constraint on the size or structure of the
   interface ID field.

   Examples of global unicast addresses that start with binary 000 are
   the IPv6 address with embedded IPv4 addresses described in section
   2.5.5 and the IPv6 address containing encoded NSAP addresses
   specified in [NSAP].  An example of global addresses starting with a
   binary value other than 000 (and therefore having a 64-bit interface
   ID field) can be found in [AGGR].

2.5.5 IPv6 Addresses with Embedded IPv4 Addresses

   The IPv6 transition mechanisms [TRAN] include a technique for hosts
   and routers to dynamically tunnel IPv6 packets over IPv4 routing
   infrastructure.  IPv6 nodes that use this technique are assigned
   special IPv6 unicast addresses that carry a global IPv4 address in
   the low-order 32 bits.  This type of address is termed an "IPv4-
   compatible IPv6 address" and has the format:

   |                80 bits               | 16 |      32 bits        |
   +--------------------------------------+--------------------------+
   |0000..............................0000|0000|    IPv4 address     |
   +--------------------------------------+----+---------------------+

   Note: The IPv4 address used in the "IPv4-compatible IPv6 address"
   must be a globally-unique IPv4 unicast address.

   A second type of IPv6 address which holds an embedded IPv4 address is
   also defined.  This address type is used to represent the addresses
   of IPv4 nodes as IPv6 addresses.  This type of address is termed an
   "IPv4-mapped IPv6 address" and has the format:



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   |                80 bits               | 16 |      32 bits        |
   +--------------------------------------+--------------------------+
   |0000..............................0000|FFFF|    IPv4 address     |
   +--------------------------------------+----+---------------------+

2.5.6 Local-Use IPv6 Unicast Addresses

   There are two types of local-use unicast addresses defined.  These
   are Link-Local and Site-Local.  The Link-Local is for use on a single
   link and the Site-Local is for use in a single site.  Link-Local
   addresses have the following format:

   |   10     |
   |  bits    |         54 bits         |          64 bits           |
   +----------+-------------------------+----------------------------+
   |1111111010|           0             |       interface ID         |
   +----------+-------------------------+----------------------------+

   Link-Local addresses are designed to be used for addressing on a
   single link for purposes such as automatic address configuration,
   neighbor discovery, or when no routers are present.

   Routers must not forward any packets with link-local source or
   destination addresses to other links.

   Site-Local addresses have the following format:

   |   10     |
   |  bits    |         54 bits         |         64 bits            |
   +----------+-------------------------+----------------------------+
   |1111111011|        subnet ID        |       interface ID         |
   +----------+-------------------------+----------------------------+

   Site-local addresses are designed to be used for addressing inside of
   a site without the need for a global prefix.  Although a subnet ID
   may be up to 54-bits long, it is expected that globally-connected
   sites will use the same subnet IDs for site-local and global
   prefixes.

   Routers must not forward any packets with site-local source or
   destination addresses outside of the site.










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2.6 Anycast Addresses

   An IPv6 anycast address is an address that is assigned to more than
   one interface (typically belonging to different nodes), with the
   property that a packet sent to an anycast address is routed to the
   "nearest" interface having that address, according to the routing
   protocols' measure of distance.

   Anycast addresses are allocated from the unicast address space, using
   any of the defined unicast address formats.  Thus, anycast addresses
   are syntactically indistinguishable from unicast addresses.  When a
   unicast address is assigned to more than one interface, thus turning
   it into an anycast address, the nodes to which the address is
   assigned must be explicitly configured to know that it is an anycast
   address.

   For any assigned anycast address, there is a longest prefix P of that
   address that identifies the topological region in which all
   interfaces belonging to that anycast address reside.  Within the
   region identified by P, the anycast address must be maintained as a
   separate entry in the routing system (commonly referred to as a "host
   route"); outside the region identified by P, the anycast address may
   be aggregated into the routing entry for prefix P.

   Note that in the worst case, the prefix P of an anycast set may be
   the null prefix, i.e., the members of the set may have no topological
   locality.  In that case, the anycast address must be maintained as a
   separate routing entry throughout the entire internet, which presents
   a severe scaling limit on how many such "global" anycast sets may be
   supported.  Therefore, it is expected that support for global anycast
   sets may be unavailable or very restricted.

   One expected use of anycast addresses is to identify the set of
   routers belonging to an organization providing internet service.
   Such addresses could be used as intermediate addresses in an IPv6
   Routing header, to cause a packet to be delivered via a particular
   service provider or sequence of service providers.

   Some other possible uses are to identify the set of routers attached
   to a particular subnet, or the set of routers providing entry into a
   particular routing domain.

   There is little experience with widespread, arbitrary use of internet
   anycast addresses, and some known complications and hazards when
   using them in their full generality [ANYCST].  Until more experience
   has been gained and solutions are specified, the following
   restrictions are imposed on IPv6 anycast addresses:




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   o  An anycast address must not be used as the source address of an
      IPv6 packet.

   o  An anycast address must not be assigned to an IPv6 host, that is,
      it may be assigned to an IPv6 router only.

2.6.1 Required Anycast Address

   The Subnet-Router anycast address is predefined.  Its format is as
   follows:

   |                         n bits                 |   128-n bits   |
   +------------------------------------------------+----------------+
   |                   subnet prefix                | 00000000000000 |
   +------------------------------------------------+----------------+

   The "subnet prefix" in an anycast address is the prefix which
   identifies a specific link.  This anycast address is syntactically
   the same as a unicast address for an interface on the link with the
   interface identifier set to zero.

   Packets sent to the Subnet-Router anycast address will be delivered
   to one router on the subnet.  All routers are required to support the
   Subnet-Router anycast addresses for the subnets to which they have
   interfaces.

   The subnet-router anycast address is intended to be used for
   applications where a node needs to communicate with any one of the
   set of routers.

2.7 Multicast Addresses

   An IPv6 multicast address is an identifier for a group of interfaces
   (typically on different nodes).  An interface may belong to any
   number of multicast groups.  Multicast addresses have the following
   format:

   |   8    |  4 |  4 |                  112 bits                   |
   +------ -+----+----+---------------------------------------------+
   |11111111|flgs|scop|                  group ID                   |
   +--------+----+----+---------------------------------------------+

         binary 11111111 at the start of the address identifies the
         address as being a multicast address.

                                       +-+-+-+-+
         flgs is a set of 4 flags:     |0|0|0|T|
                                       +-+-+-+-+



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