user manual

CDP runs on all media that support Subnetwork Access Protocol (SNAP). Because CDP runs over the data-link
layer only, two systems that support different network-layer protocols can learn about each other.
Each CDP-configured device sends periodic messages to a multicast address, advertising at least one address
at which it can receive SNMP messages. The advertisements also contain time-to-live, or holdtime information,
which is the length of time a receiving device holds CDP information before discarding it. Each device also
listens to the messages sent by other devices to learn about neighboring devices.
On the switch, CDP enables Network Assistant to display a graphical view of the network. The switch uses
CDP to find cluster candidates and maintain information about cluster members and other devices up to three
cluster-enabled devices away from the command switch by default.
CDP and Stacks
A switch stack appears as a single switch in the network. Therefore, CDP discovers the switch stack, not the
individual stack members. The switch stack sends CDP messages to neighboring network devices when there
are changes to the switch stack membership, such as stack members being added or removed.
Default CDP Configuration
This table shows the default CDP configuration.
Default SettingFeature
EnabledCDP global state
EnabledCDP interface state
60 secondsCDP timer (packet update frequency)
180 secondsCDP holdtime (before discarding)
EnabledCDP Version-2 advertisements
How to Configure CDP
Configuring CDP Characteristics
You can configure these CDP characteristics:
•
Frequency of CDP updates
•
Amount of time to hold the information before discarding it
•
Whether or not to send Version-2 advertisements
Steps 2 through 4 are all optional and can be performed in any order.Note
Catalyst 2960-X Switch Network Management Configuration Guide, Cisco IOS Release 15.0(2)EX
34 OL-29044-01
Configuring the Cisco Discovery Protocol
CDP and Stacks