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.
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 (In our Implementation 0x01 will be used in this release) |
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 |
The following list identifies the different types of TLVs.
This TLV is used to identify Device name in form of Character string. In EXOS-CDP implementation it will be the configurable value. System Mac address will be the default Device Id.
This TLV contains a number that indicates how many addresses are contained in the packet, followed by one entry for each address being advertised. The addresses advertised are the ones assigned to the interface on which the CDP message is sent. A device can advertise all addresses for a given protocol suite and, optionally, can advertise one or more loopback IP addresses. If the device can be managed by SNMP, the first entry in the address type/length/value is an address at which the device receives SNMP messages. Maximum of 32 IP address are supported.
The following table identifies and describes the various fields in the Address Information TLV.
Field | Description |
---|---|
Protocol Type |
Protocol type It can be one of the following values
|
Length | Length of the protocol field. |
Protocol |
One of the following values:
|
Address Length | Length of the address fields in bytes |
Address | Address of the interface or the address of the system if addresses are not assigned to the interface. |
The port ID type/length/value contains an ASCII character string that identifies the port on which the CDP message is sent. The type/length/value length determines the length of the string. In EXOS-CDP port description from the Pif structure is added in this TLV. If this Value is NULL then it will be the slot and port information.
The capability TLV describes the device‘s functional capability. It can be set to one of the bits listed below.
The following table identifies and describes the various bits in the Capabilities TLV.
Bit Description | Bit Description |
---|---|
0x01 | Performs level 3 routing for at least one network layer protocol. |
0x02 | Performs level 2 transparent bridging. |
0x04 | Performs level 2 source-route bridging. A source-route bridge would set both this bit and bit 0x02. |
0x08 | Performs level 2 switching. The difference between this bit and bit 0x02 is that a switch does not run the STP. |
0x10 |
Sends and receives packets for at least one network layer protocol. If the device is routing the protocol, this Bit should not be set. |
0x20 | The bridge or switch does not forward IGMP Report packets on non-router ports. |
0x40 | Provides level 1 functionality. |
The version TLV contains a character string that provides information about the software release version that the device is running. In EXOS-CDP version will be software version.
The platform TLV contains an ASCII character string that describes the hardware platform of the device. These platform TLV values are EXOS platform information that is the same seen when you issue the show switch command.
Here are some of the possible string platform values