📖 正确答案: A
【In-Depth Analysis】
• Core Principle: To map a multivendor network, the neighbor-discovery protocol must be vendor-neutral. LLDP (IEEE 802.1AB) is the open standard for this job, while CDP is Cisco-proprietary and is only understood by Cisco devices. On Cisco devices LLDP is enabled globally with lldp run.
• Option Breakdown:

• A (Correct): lldp run enables LLDP globally; non-Cisco devices can read it, so it works for a multivendor topology map.
• B (Incorrect): cdp run enables CDP, which is Cisco-proprietary and cannot discover non-Cisco neighbors.
• C (Incorrect): cdp enable is an interface-level command (not global), and it is still just CDP.
• D (Incorrect): flow-sampler-map belongs to NetFlow traffic sampling and has nothing to do with neighbor discovery.

• Quick Memory Trick: "Multivendor means L for LLDP; Cisco-only means C for CDP."

【Practical Extension】
Cisco devices usually run CDP by default, whereas LLDP often has to be enabled manually with lldp run; then use show lldp neighbors to view the results. A typical case is a closet that mixes Cisco switches with other vendors' switches, IP phones or access points, where CDP alone produces a topology with gaps. Keep in mind that LLDP advertises device information to neighbors, so consider disabling it on untrusted, outward-facing ports.