EXOS CDP Support

The ExtremeXOS-CDP implementation gathers information about network neighbors that support the Cisco Discovery protocol. This includes edge devices (VoIP phones) in the network-edge domain.

EXOS-CDP runs on top of the controlled port of an 802 MAC client. If port access is controlled by IEEE 802.1X, the port must be authorized before you enable CDP protocol receive functionality. CDP also runs over an aggregated MAC client, and the CDP protocol information must run over all the physical MAC clients of the aggregated ports. The spanning tree state of a port does not affect the transmission of CDP PDUs.

Each CDP message contains information identifying the source port as a connection endpoint identifier. It also contains at least one network address that can be used by an NMS to reach a management agent on the device (through the indicated source port). Each CDP message contains a time-to-live value, which tells the recipient when to discard each element of learned topology information.

By default EXOS-CDP feature is disabled.

Both CDP version 1 and version 2 are supported in EXOS-CDP implementation.

CDP Packet Format

The CDP control packets are encapsulated to the Sub-network Access Protocol (SNAP), and are sent as multicasts with Cisco®-defined multicast MAC address 01:00:0C:CC:CC:CC.

The following table lists and describes the CDP packet fields.

Field Description
Version Version of the CDP being used values 0x1 or 0x02
Time-to-Live (TTL) TTL indicates the amount of time in seconds that a receiver should retain the information contained in this packet.
Check Sum Standard IP checksum
Type Indicates the type of the TLV
Length Indicates the total length of the Type,Length,Value fields
Value Indicates the value of the TLV

Different Types of TLVs

The following list identifies the different types of TLVs.