一、33:33 由来
1. RFC9542 - 2024-05-02
Note
IANA allocates addresses under the IANA OUI (00-00-5E) as explained in [RFC9542]. Unicast addresses under the IANA OUI start with 00-00-5E, while multicast addresses under the IANA OUI start with 01-00-5E. In the lists below, these initial 3 bytes are omitted for brevity. As described in [RFC9542], 48-bit MAC addresses in the range 33-33-00-00-00-00 to 33-33-FF-FF-FF-FF are used for IPv6 multicast.
IANA 在 [RFC9542] 中指定了对 IANA OUI（00-00-5E）下地址的分配。该 OUI 下的单播地址以 00-00-5E 开头，而多播地址以 01-00-5E 开头。为简洁起见，列表中省略了该前 3 个字节。根据 [RFC9542] 描述，范围在 33-33-00-00-00-00 到 33-33-FF-FF-FF-FF 的 48 位 MAC 地址用于 IPv6 多播。
When the available space for either multicast or unicast EUI-48 identifiers under OUI 00-00-5E has been 90% or more exhausted, IANA should request an additional OUI from the IEEE Registration Authority
for further IANA assignment use. The appointed Expert (s) should monitor for this condition and notify IANA.
当在 OUI 00-00-5E 下可用于多播或单播 EUI-48 标识符的空间已经耗尽 90% 或更多时，IANA 应该向 IEEE 注册管理机构请求另一个 OUI，以继续将来为 IANA 分配使用。指定的专家应监测此情况并通知 IANA。
2. RFC9542 - April 2024
2.3. Other 48-Bit MAC Identifiers Used by the IETF
IETF 使用的其他 48 位 MAC 标识符
There are two other blocks of 48-bit MAC identifiers that are used by the IETF as described below.
由 IETF 使用的另外两个块 48 位 MAC 标识符，如下所述。
2.3.1. Identifiers with a '33-33' Prefix
带有 ' 33-33 ' 前缀的标识符
All 48-bit multicast MAC identifiers prefixed with "33-33" (that is, the 2**32 multicast MAC identifiers in the range from 33-33-00-00-00-00 to 33-33-FF-FF-FF-FF) are used as specified in [RFC2464] for IPv6 multicast. In all of these identifiers, the Group bit (the bottom bit of the first octet) is on, as is required to work properly with existing hardware as a multicast identifier. They also have the Local bit on, but any Ethernet using standard IPv6 multicast should note that these addresses will be used for that purpose. These multicast MAC addresses fall into the Administratively Assigned SLAP quadrant.
所有以 "33-33" 作为前缀的 48 位多播 MAC 标识符（即，位于从 33-33-00-00-00-00 到 33-33-FF-FF-FF-FF 范围内的 2**32 个多播 MAC 标识符）用于 IPv6 多播，如 [RFC2464] 中指定的。
在所有这些标识符中，Group 位(第一个八位字节的底部位)都是打开的，这是作为多播标识符与现有硬件正常工作所必需的。它们还具有本地位，但任何使用标准 IPv6 多播的以太网应注意到这些地址将用于此目的。这些多播 MAC 地址属于管理分配的 SLAP（ Structured Local Address Plan，结构化本地地址规划） 范围。
Historical Notes: It was the custom during IPv6 design to use "3" for unknown or example values, and 3333 Coyote Hill Road, Palo Alto, California is the address of PARC (Palo Alto Research Center), formerly "Xerox PARC." Ethernet was originally specified by the Digital Equipment Corporation, Intel Corporation, and Xerox Corporation. The pre-IEEE [IEEE.802.3_2012] Ethernet protocol has sometimes been known as "DIX" Ethernet from the first letters of the names of these companies.
历史背注：在 IPv6 设计期间，习惯使用 "3" 作为未知或示例值，而加利福尼亚州帕洛阿尔托的 Coyote Hill Road 3333 号是帕克（Palo Alto Research Center）的地址，曾为 "施乐帕克（Xerox PARC）"。以太网最初是由数字设备公司、英特尔公司和施乐公司指定的。基于公司名称的首字母，IEEE[802.3_2012] 之前的以太网协议有时被称为 "DIX" 以太网。
3. RFC 2464 - 1998
7. Address Mapping -- Multicast
地址映射 ------ 多播
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.
一个包含多播目的地址 DST 的 IPv6 数据包，由 DST [1] 到 DST [16] 组成，将被发送到以太网的多播地址，其前两个八位字节的值为 3333（十六进制），最后四个八位字节与 DST 的最后四个八位字节相同。
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0 0 1 1 0 0 1 1|0 0 1 1 0 0 1 1|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| DST [13] | DST [14] |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| DST [15] | DST [16] |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
二、IPv6 ND（Neighbor Discovery，邻居发现）中的 MAC 33:33
Neighbor Discovery Process is multicast based.
邻居发现过程是基于组播的。
1. Router Discovery process
| 类型 | 地址 | 含义 |
|---|---|---|
| RS destination MAC address | 33:33:00:00:00:02 | all-routers multicast MAC address |
| RA destination MAC address | 33:33:00:00:00:01 | all-nodes multicast MAC address |
2. Address Resolution process
| 类型 | 地址 | 含义 |
|---|---|---|
| NS destination MAC address | 33:33:FF:xx:xx:xx | solicited node multicast MAC address |