To permit the discovery of non-Cisco devices, Cisco devices also support LLDP, a vendor-neutral device discovery protocol defined by IEEE 802.1AB standard. LLDP allows network devices to advertise information about themselves to other devices on the network. This protocol runs over the data link layer, which allows two systems running different network-layer protocols to learn about each other.
為了讓非 Cisco 裝置也能被探索，Cisco 裝置也支援 LLDP，這是一種由 IEEE 802.1AB 標準定義、與廠商無關的裝置探索協定。LLDP 允許網路裝置向網路上的其他裝置通告自身的資訊。此協定在資料鏈結層上運作，讓執行不同網路層協定的兩個系統也能互相得知對方的資訊。
LLDP is a protocol that transmits information about the capabilities and the status of a device and its interfaces. LLDP devices use the protocol to solicit information only from other LLDP devices.
LLDP 是一種傳輸裝置及其介面能力與狀態資訊的協定。LLDP 裝置只會向其他 LLDP 裝置徵求資訊。
LLDP supports a set of attributes that it uses to discover other devices. These attributes contain type, length, value (TLV) descriptions. TLVs are blocks of information embedded in LLDP advertisements, giving details about optional information elements such as IP address, Device ID, and Platform. LLDP devices can use TLVs to send and receive information to other devices on the network. Using this protocol, devices can advertise details such as configuration information, device capabilities, and device identity.
LLDP 支援一組屬性，用來探索其他裝置。這些屬性包含類型、長度、值（TLV）描述。TLV 是嵌入在 LLDP 通告中的資訊區塊，提供諸如 IP 位址、裝置 ID、平台等選用資訊元素的詳細內容。LLDP 裝置可利用 TLV 向網路上的其他裝置傳送與接收資訊。透過此協定，裝置可以通告設定資訊、裝置能力與裝置身分等詳細內容。
Some of the TLVs that are advertised by LLDP:
LLDP 所通告的部分 TLV：
- Management address: the IP address used to access the device for management (configuring and verifying the device)管理位址：用於存取裝置進行管理（設定與驗證裝置）的 IP 位址
- System capabilities: different hardware and software specifications of the device系統能力：裝置的各種硬體與軟體規格
- System name: the hostname that was configured on that device系統名稱：該裝置上設定的主機名稱
After you globally enable LLDP, it is enabled for transmit and receive on all supported interfaces by default. The lldp transmit command enables the transmission of LLDP packets on an interface. Thelldpreceive command enables the reception of LLDP packets on an interface.
全域啟用 LLDP 後，所有支援的介面預設都會啟用傳送與接收功能。lldp transmit 指令可在介面上啟用 LLDP 封包的傳送。lldpreceive 指令可在介面上啟用 LLDP 封包的接收。
The show lldp neighbors command displays information about neighbors, including device ID, interface type and number, hold time settings, capabilities, and port ID.
show lldp neighbors 指令會顯示鄰居的相關資訊，包括裝置 ID、介面類型與編號、保留時間設定、能力，以及連接埠 ID。
R1# show lldp neighbors
Capability codes:
(R) Router, (B) Bridge, (T) Telephone, (C) DOCSIS Cable Device
(W) WLAN Access Point, (P) Repeater, (S) Station, (O) Other
Device ID Local Intf Hold-time Capability Port ID
R2 Et0/2 120 R Et0/2
R3 Et0/1 120 R Et0/2
Total entries displayed: 2The output in the example tells you that router R1 has two neighbors, R2 and R3. Both devices have routing functionality. The interfaces to reach them through are Ethernet0/1 and Etherne0/2. This output contains information only about the neighbors that support LLDP and have it configured to exchange information.
範例中的輸出顯示路由器 R1 有兩個鄰居，R2 與 R3。這兩台裝置都具備路由功能。連接到它們的介面分別是 Ethernet0/1 與 Etherne0/2。此輸出僅包含支援 LLDP 且已設定交換資訊的鄰居資訊。