Here you will observe where Open Systems Interconnection (OSI) Layer 2 (corresponding to the TCP/IP link layer) addresses fit into the host-to-host packet delivery process.
在此，你將觀察開放式系統互連（OSI）第 2 層（對應 TCP/IP 鏈結層）位址在主機對主機封包傳遞流程中所扮演的角色。
Layer 2 Ethernet LANs have the following characteristics:
第 2 層 Ethernet LAN 具有以下特性：
- They use MAC addresses.使用 MAC 位址。
- They identify end devices in the LAN.識別 LAN 中的終端裝置。
- They enable the packet to be carried by the local media across each segment.使封包能透過本地傳輸媒介跨越每個區段傳送。
Layer 2 defines how data is formatted for transmission and how access to the physical media is controlled. Layer 2 devices provide an interface with the physical media. Some common examples are network interface cards (NICs) installed in a host.
第 2 層定義資料如何格式化以進行傳輸，以及如何控制對實體傳輸媒介的存取。第 2 層裝置提供與實體傳輸媒介的介面，常見的例子是安裝在主機上的網路介面卡（NIC）。
Device-to-device communications require Layer 2 addresses, also known as physical addresses. For example, Ethernet physical addresses or MAC addresses are embedded in Ethernet NIC in end devices, such as hosts.
裝置與裝置之間的通訊需要第 2 層位址，也稱為實體位址。例如，Ethernet 實體位址或 MAC 位址會內嵌在終端裝置（如主機）的 Ethernet NIC 中。
Although MAC addresses are unique, physical addresses are not hierarchical. They are associated with a particular device, regardless of its location or connected network. These Layer 2 addresses have no meaning outside the local network media. They are used to locate the end devices in the local physical network on the data link layer.
雖然 MAC 位址是唯一的，但實體位址並不具階層性。它們與特定裝置相關聯，與該裝置的位置或所連接的網路無關。這些第 2 層位址在本地網路傳輸媒介之外沒有意義，它們用於在資料鏈結層識別本地實體網路中的終端裝置。
An Ethernet MAC address is a two-part, 48-bit binary value that is expressed as 12 hexadecimal digits. The address formats might appear like 00-05-9A-3C-78-00, 00:05:9A:3C:78:00, or 0005.9A3C.7800.
Ethernet MAC 位址是一個由兩部分組成的 48 位元二進位值，以 12 個十六進位數字表示。位址格式可能呈現為 00-05-9A-3C-78-00、00:05:9A:3C:78:00，或 0005.9A3C.7800。
All devices that are connected to an Ethernet LAN have MAC-addressed interfaces. The NIC uses the MAC address in received frames to determine if a message should be passed to the upper layers for processing. The MAC address is permanently encoded into a ROM chip on a NIC. The MAC address is made up of the Organizationally Unique Identifier (OUI) and the vendor assignment number.
所有連接到 Ethernet LAN 的裝置皆具有 MAC 定址的介面。NIC 會利用收到的框架中的 MAC 位址，判斷是否應將訊息傳遞至上層進行處理。MAC 位址永久編碼於 NIC 上的 ROM 晶片中，由組織唯一識別碼（OUI）與廠商指派編號組成。
Switches also have MAC addresses, but a device only sends a frame to these addresses when communicating with the switch, for example, for management. Otherwise, frames are addressed for other devices, and the switch forwards the frames to those devices.
交換器也有 MAC 位址，但裝置僅在與交換器通訊時（例如進行管理作業）才會將框架傳送至這些位址。否則，框架會定址給其他裝置，並由交換器將框架轉送給那些裝置。
The figure shows the Layer 2 (L2) addresses on two PCs and a router. Note that the router has different MAC addresses on each interface.
此圖顯示兩台電腦與一台路由器上的第 2 層（L2）位址。請注意，該路由器的每個介面都有不同的 MAC 位址。