1-6This is the fast sending mechanism of LLDP. With this mechanism, a specific number of LLDPDUs aresent successively at the 1-second interval to help LLDP neighbors discover the local device as soon aspossible. Then, the normal LLDPDU transit interval resumes.Receiving LLDPDUsAn LLDP-enabled port operating in TxRx mode or Rx mode checks the TLVs carried in every LLDPDUit receives for validity violation. If valid, the information is saved and an aging timer is set for it based onthe time to live (TTL) TLV carried in the LLDPDU. If the TTL TLV is zero, the information is aged outimmediately.Compatibility of LLDP with CDPYou need to enable CDP compatibility for your device to work with Cisco IP phones.As your LLDP-enabled device cannot recognize Cisco Discovery Protocol (CDP) packets, it does notrespond to the requests of Cisco IP phones for the voice VLAN ID configured on the device. This cancause a requesting Cisco IP phone to send voice traffic untagged to your device, disabling your deviceto differentiate voice traffic from other types of traffic.By configuring CDP compatibility, you can enable LLDP on your device to receive and recognize CDPpackets from Cisco IP phones and respond with CDP packets carrying the voice VLAN configurationTLV for the IP phones to configure the voice VLAN automatically. Thus, the voice traffic is confined inthe configured voice VLAN to be differentiated from other types of traffic.CDP-compatible LLDP operates in one of the follows two modes:z TxRx, where CDP packets can be transmitted and received.z Disable, where CDP packets can neither be transmitted nor be received.Protocols and StandardsThe protocols and standards related to LLDP include:z IEEE 802.1AB-2005, Station and Media Access Control Connectivity Discoveryz ANSI/TIA-1057, Link Layer Discovery Protocol for Media Endpoint DevicesConfiguring LLDPLLDP Configuration Task ListPerform the tasks in Table 1-1 to configure LLDP:Table 1-7 LLDP configuration task listTask RemarksEnabling LLDP on PortsOptionalBy default, LLDP is enabled on ports.Make sure that LLDP is also enabled globally, because LLDP can workon a port only when it is enabled both globally and on the port.
