Port Discovery with LLDP and CDP

The GigaVUE HC Series is capable of snooping Link Layer Discovery Protocol (LLDP) packets and Cisco Discovery Protocol (CDP) packets. If the devices in your network use either of these protocols, a GigaVUE HC Series node can identify its immediate neighbors and their capabilities. Snooped LLDP and CDP information includes the remote port and chassis IDs, as well as other selected information, if it is included by the sender. This information can be used to determine the origin of traffic flows.

All GigaVUE HC Series and TA Series nodes support LLDP and CDP port discovery,

LLDP and CDP are physical topology discovery protocols (Layer 2). The protocols are unidirectional. Devices send their identity and capabilities in a packet. The GigaVUE HC Series node receives the packet and extracts information from it, such as the chassis ID and port ID of a neighbor. The information from the neighbors varies depending on what is sent in the packet.

An LLDP packet supports the following capabilities in a type-length-value (TLV) structure. The first four capabilities are mandatory.

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Chassis ID

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Port ID

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Time-to-Live (TTL)

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End of TLVs

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Port description

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System name

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System description

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System capabilities available

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System capabilities enabled

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VLAN name

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Management address

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Port VLAN ID

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Management VLAN ID

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Link Aggregation port ID

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Link Aggregation status

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Maximum Transmission Unit (MTU)

A CDP packet supports the following capabilities in a TLV structure:

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Device ID

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Port ID

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Platform

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Software version

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Native VLAN ID

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Capabilities

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Network prefix address

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Network prefix mask

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Interface address

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Management address

The LLDP/CDP discovery packets are copied and parsed by the GigaVUE HC Series node, and the neighbor information is cached. Discovery packets are not terminated on the GigaVUE HC Series node, nor are they removed from the ingress data stream.

Notes:

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Port discovery can be enabled on network, tool, and circuit type ports.

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Use port discovery on ports fed by SPAN ports or aggregators with caution. LLDP/CDP information received from a SPAN port may be misleading, depending on how it is configured. When a large range of ports are SPANed, different and conflicting LLDP/CDP information may be received. LLDP/CDP is best used on TAPed network interfaces.