H3C Technologies H3C S5560 Series Switches - Manual (Page 282)

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Configuring CDP compatibility
When the switch is directly connected to a Cisco device that supports only CDP rather than LLDP, you can
enable CDP compatibility to enable the switch to exchange information with the directly-connected
device.
CDP compatibility enables the switch to use LLDP to receive and recognize CDP packets from the
directly-connected device and send CDP packets to the directly-connected device. The packets that the
switch sends to the neighboring CDP device carry the following information:
• Device ID.
• ID of the port connecting to the neighboring device.
• port IP address.
• PVID.
• TTL.
The port IP address is the primary IP address of the VLAN interface in up state. The VLAN ID of the VLAN
interface must be the lowest among the VLANs permitted on the port. If no VLAN interfaces of the
permitted VLANs is assigned an IP address or all VLAN interfaces are down, no port IP address will be
advertised.
The CDP neighbor-information-related fields in the output of the display lldp neighbor-information
command show the CDP neighboring device information that can be recognized by the switch. For more
information about the display lldp neighbor-information command, see Layer 2—LAN Switching
Command Reference.
If your LLDP-enabled device cannot recognize CDP packets, it does not respond to the requests of Cisco
IP phones for the voice VLAN ID configured on the device. As a result, a requesting Cisco IP phone sends
voice traffic without any VLAN tag to your device. Your device cannot differentiate the voice traffic from
other types of traffic.
CDP compatibility enables your device to receive and recognize CDP packets from a Cisco IP phone and
respond with CDP packets carrying TLVs with the voice VLAN configuration. According to TLVs with the
voice VLAN configuration, the IP phone automatically configures the voice VLAN. As a result, the voice
traffic is confined in the configured voice VLAN and is differentiated from other types of traffic.
For more information about voice VLANs, see "Configuring voice VLANs."
Configuration prerequisites
Before you configure CDP compatibility, complete the following tasks:
• Globally enable LLDP.
• Enable LLDP on the port connecting to a device supporting CDP.
• Configure LLDP to operate in TxRx mode on the port.
Configuration procedure
CDP-compatible LLDP operates in one of the following modes:
• TxRx—CDP packets can be transmitted and received.
• Disable—CDP packets cannot be transmitted or received.