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 tag to your device, and, as a result, your device cannot differentiate the voice
traffic from other types of traffic.
With CDP compatibility enabled, your device can receive and recognize CDP packets from a Cisco IP
phone and respond with CDP packets, which carry the voice VLAN configuration TLVs. According to the
voice VLAN configuration TLVs, the IP phone automatically configures the voice VLAN. As a result, the
voice traffic is confined in the configured voice VLAN, and differentiated from other types of traffic.
Before you configure CDP compatibility, complete the following tasks:
Globally enable LLDP.
Enable LLDP on the port connecting to an IP phone and configure the port to operate in TxRx mode.
Configuring CDP compatibility
CDP-compatible LLDP operates in one of the following modes:
TxRx: CDP packets can be transmitted and received.
Disable: CDP packets can be neither transmitted nor received.
LLDP traps are sent periodically, and the interval is configurable. To make CDP-compatible LLDP take
effect on certain ports, first enable CDP-compatible LLDP globally, and then configure CDP-compatible
LLDP to operate in TxRx mode.
Follow these steps to enable LLDP to be compatible with CDP:
Enter system view
Enable CDP compatibility globally
view or port
Configure CDP-compatible LLDP to
operate in TxRx mode
The maximum TTL value that CDP allows is 255 seconds. To make CDP-compatible LLDP work properly
with Cisco IP phones, be sure that the product of the TTL multiplier and the LLDPDU transmit interval is less
than 255 seconds.
Use the command...
lldp compliance cdp
Enter Layer 2
interface interface-type interface-number
Enter port group
port-group manual port-group-name
lldp compliance admin-status cdp txrx
Disabled by default.
Use either command.
Disable mode by default