rfc2464

Copyright Notice

   Copyright (C) The Internet Society (1998).  All Rights Reserved.

1.  Introduction

   This document specifies the frame format for transmission of IPv6
   packets and the method of forming IPv6 link-local addresses and
   statelessly autoconfigured addresses on Ethernet networks.  It also
   specifies the content of the Source/Target Link-layer Address option
   used in Router Solicitation, Router Advertisement, Neighbor
   Solicitation, Neighbor Advertisement and Redirect messages when those
   messages are transmitted on an Ethernet.
   这篇文档描述了如何生成IPv6的祯，在以太网中生成IPv6链路本地地址和无状态自动地址配置的方法。
   另外还讲述了在以太网中ND各报文的源或目的链路地址选项的内容。

   This document replaces RFC 1972, "A Method for the Transmission of
   IPv6 Packets over Ethernet Networks", which will become historic.

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC 2119].

2.  Maximum Transmission Unit

   The default MTU size for IPv6 [IPV6] packets on an Ethernet is 1500
   octets.  This size may be reduced by a Router Advertisement [DISC]
   containing an MTU option which specifies a smaller MTU, or by manual
   configuration of each node.  If a Router Advertisement received on an
   Ethernet interface has an MTU option specifying an MTU larger than
   1500, or larger than a manually configured value, that MTU option may
   be logged to system management but must be otherwise ignored.
   以太网中的默认IPv6的MTU为1500字节。大小可能因为RA中的MTU小于该值而减小，或手动配置一个
   较小的MTU。如果以太网接口接收到了一个包含超过1500的MTU选项的RA的时候，或大于手动配置的
   默认MTU，则这个MTU选项可能被记录，但在其他情况下，必须被忽略。

Crawford                    Standards Track                     [Page 1]
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RFC 2464               IPv6 Packets over Ethernet          December 1998

   For purposes of this document, information received from DHCP is
   considered "manually configured" and the term Ethernet includes
   CSMA/CD and full-duplex subnetworks based on ISO/IEC 8802-3, with
   various data rates.
   为了这篇文档能更好的理解，可以认为从DHCP服务器获得的信息是手动配置的，认为以太网包括CSMA/CD和全双工
   子网。

3.  Frame Format

   IPv6 packets are transmitted in standard Ethernet frames.  The
   Ethernet header contains the Destination and Source Ethernet
   addresses and the Ethernet type code, which must contain the value
   86DD hexadecimal.  The data field contains the IPv6 header followed
   immediately by the payload, and possibly padding octets to meet the
   minimum frame size for the Ethernet link.
   IPv6数据报都被封装在标准的以太网祯中。以太网头包含目的和源以太网地址，以及以太网类型，
   这个类型值必须为0x86DD。在数据区域包含了IPv6头以及负债，并且可能包含了填充字段以保证
   祯的最小长度符合链路的最小祯的要求。

                     0                   1
                     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
                    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                    |          Destination          |
                    +-                             -+
                    |            Ethernet           |
                    +-                             -+
                    |            Address            |
                    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                    |             Source            |
                    +-                             -+
                    |            Ethernet           |
                    +-                             -+
                    |            Address            |
                    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                    |1 0 0 0 0 1 1 0 1 1 0 1 1 1 0 1|
                    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                    |             IPv6              |
                    +-                             -+
                    |            header             |
                    +-                             -+
                    |             and               |
                    +-                             -+
                    /            payload ...        /
                    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                    (Each tic mark represents one bit.)

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RFC 2464               IPv6 Packets over Ethernet          December 1998

4.  Stateless Autoconfiguration

   The Interface Identifier [AARCH] for an Ethernet interface is based
   on the EUI-64 identifier [EUI64] derived from the interface's built-
   in 48-bit IEEE 802 address.  The EUI-64 is formed as follows.
   (Canonical bit order is assumed throughout.)
   以太网接口标识符按照EUI-64标识符的标准格式，从接口的48位IEEE地址转化而来（网卡mac地址），
   以下是转化的规则和步骤。

   The OUI of the Ethernet address (the first three octets) becomes the
   company_id of the EUI-64 (the first three octets).  The fourth and
   fifth octets of the EUI are set to the fixed value FFFE hexadecimal.
   The last three octets of the Ethernet address become the last three
   octets of the EUI-64.
   网卡mac地址的前3个字节（即OUI）成为EUI-64的company_id。EUI地址的第4－5字节为确定值0xFFFE。
   网卡mac地址的最后3个字节成为EUI-64地址的最后3个字节。

   The Interface Identifier is then formed from the EUI-64 by
   complementing the "Universal/Local" (U/L) bit, which is the next-to-
   lowest order bit of the first octet of the EUI-64.  Complementing
   this bit will generally change a 0 value to a 1, since an interface's
   built-in address is expected to be from a universally administered
   address space and hence have a globally unique value.  A universally
   administered IEEE 802 address or an EUI-64 is signified by a 0 in the
   U/L bit position, while a globally unique IPv6 Interface Identifier
   is signified by a 1 in the corresponding position.  For further
   discussion on this point, see [AARCH].
   然后把原来的mac地址的"Universal/Local"(U/L)标志位取补。即如果原来是1，则变为0；如果
   原来是0，则变为1。
  

   For example, the Interface Identifier for an Ethernet interface whose
   built-in address is, in hexadecimal,

                             34-56-78-9A-BC-DE

   would be

                         36-56-78-FF-FE-9A-BC-DE.

   A different MAC address set manually or by software should not be
   used to derive the Interface Identifier.  If such a MAC address must
   be used, its global uniqueness property should be reflected in the
   value of the U/L bit.
   一个手动或由软件生成的MAC地址不应该被用来生成接口标识符。如果必须用他来生成接口标识符，则
   应该注意它的U/L位。

   An IPv6 address prefix used for stateless autoconfiguration [ACONF]
   of an Ethernet interface must have a length of 64 bits.
   通过无状态自动配置的以太网接口地址的ipv6地址前缀一定为64位。

Crawford                    Standards Track                     [Page 3]
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RFC 2464               IPv6 Packets over Ethernet          December 1998

5.  Link-Local Addresses

   The IPv6 link-local address [AARCH] for an Ethernet interface is
   formed by appending the Interface Identifier, as defined above, to
   the prefix FE80::/64.
   以太网IPv6链路本地地址是通过将接口标识符和64位的网络前缀FE80::/64连接生成。

       10 bits            54 bits                  64 bits
     +----------+-----------------------+----------------------------+
     |1111111010|         (zeros)       |    Interface Identifier    |
     +----------+-----------------------+----------------------------+

6.  Address Mapping -- Unicast

   The procedure for mapping IPv6 unicast addresses into Ethernet link-
   layer addresses is described in [DISC].  The Source/Target Link-layer
   Address option has the following form when the link layer is
   Ethernet.
   将IPv6单播地址影射到以太网链路地址在[DISC]中描述。以太网中的源或目的链路地址选项的
   格式如下图所示：

                    0                   1
                    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
                   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                   |     Type      |    Length     |
                   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                   |                               |
                   +-          Ethernet           -+
                   |                               |
                   +-           Address           -+
                   |                               |
                   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Option fields:

   Type        1 for Source Link-layer address.
               2 for Target Link-layer address.

   Length      1 (in units of 8 octets).

   Ethernet Address
               The 48 bit Ethernet IEEE 802 address, in canonical bit
               order.  This is the address the interface currently
               responds to, and may be different from the built-in
               address used to derive the Interface Identifier.
               这个地址是接口正在使用的地址，它有可能与生成接口标识符的地址不同。

Crawford                    Standards Track                     [Page 4]
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RFC 2464               IPv6 Packets over Ethernet          December 1998

7.  Address Mapping -- Multicast

   An IPv6 packet with a multicast destination address DST, consisting
   of the sixteen octets DST[1] through DST[16], is transmitted to the
   Ethernet multicast address whose first two octets are the value 3333
   hexadecimal and whose last four octets are the last four octets of
   DST.
   IPv6多播地址映射成以太网链路地址的方法是：取出多播地址的后4个字节，放在
   2个字节的固定值后面，形成6个字节的以太网链路地址。这2个字节的固定值为0x3333。

                  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                  |0 0 1 1 0 0 1 1|0 0 1 1 0 0 1 1|
                  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                  |   DST[13]     |   DST[14]     |
                  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                  |   DST[15]     |   DST[16]     |
                  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+