Information About CDP
The Cisco Discovery Protocol (CDP), which runs over the data link layer, is used to advertise information to all attached Cisco devices and to discover and view information about attached Cisco devices. CDP runs on all Cisco-manufactured equipment.
Each device that you configure for CDP sends periodic advertisements to a multicast address. Each device advertises at least one address at which it can receive SNMP messages. The advertisements also contain hold time information, which indicates the length of time that a receiving device should hold CDP information before discarding it. You can configure the advertisement or refresh timer and the hold timer.
CDP Version 2 (CDPv2) allows you to track instances where the native VLAN ID or port duplex states do not match between connecting devices.
CDP advertises the following type-length-value fields (TLVs):
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Device ID
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Address
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Port ID
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Capabilities
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Version
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Platform
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Native VLAN
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Full/half duplex
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Maximum Transmission Unit (MTU)
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Sysname
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SysObjectID
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Management address
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Physical location
All CDP packets include a VLAN ID. The CDP packet is untagged, so it goes over the native/access VLAN, which is then also added to the packet.
High Availability
Stateless restarts are supported for CDP. After a reboot or a supervisor switchover, the running configuration is applied.