Discovery Protocol By Cisco

2. Cisco Discovery Protocol is a proprietary, media independent layer 2 protocol used to share information about hardware platform, software version and other capabilities between neighbors devices such as routers, switches, wireless controllers, access points and IP phones. CDP is enabled by default and packets are sent out by the device every 60 seconds to the same multicast MAC address of VTP which is 01-00-0C-CC-CC-CC. CDP can be also used to share IP subnet prefixes when implementing on-demand routing (ODR).
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4. On Access Points, CDP is enabled on the radio interface only if this is connected to another infrastructure device such as another AP or Bridge.
5. Why is CDP important?
6. Besides telling you which devices are connected to which interfaces and besides supporting on-demand routing, CDP is used to provide intelligent power management between Cisco switches and Cisco access points. 
7. A Cisco 1240AG access point for example, requires 12.95 W of power (this value can grow up to 15.4 W with a long CAT 5 Ethernet cable due to dissipation) for full power operation with both radios, but only needs 6.3 W of power when operating in low power mode with both radios disabled. To help avoid an over-current condition with low power sources and to optimize power usage on Cisco switches, Cisco developed Intelligent Power Management, which uses CDP to allow powered devices (such as the access point) to negotiate with a Cisco switch for sufficient power. Please note that this is different from the 802.3af PoE classification and it works on top of it.
8. If the switch can provide sufficient inline power but its IOS version does not support the Intelligent Power Management feature, you can get CDP error messages on the AP and both radio interfaces will not come up. In this case you will need to configure the AP to use a pre-standard inline power mode with the command power online negotiation prestandard source. This indicates to the AP that the switch does not support the intelligent power management and therefore the AP will never attempt to go into low power mode.