About LLDP
The Cisco Discovery Protocol (CDP) is a device discovery protocol that allows network management applications to automatically discover and learn about other Cisco devices that are connected to the network.
To permit the discovery of non-Cisco devices, the switch also supports the Link Layer Discovery Protocol (LLDP), a vendor-neutral device discovery protocol that is defined in the IEEE 802.1ab standard. LLDP allows network devices to advertise information about themselves to other devices on the network. This protocol runs over the data-link layer, which allows two systems running different network layer protocols to learn about each other.
LLDP is a one-way protocol that transmits information about the capabilities and current status of a device and its interfaces. LLDP devices use the protocol to solicit information only from other LLDP devices.
LLDP supports a set of attributes that it uses to discover other devices. These attributes contain type, length, and value (TLV) descriptions. LLDP devices can use TLVs to send and receive information to other devices on the network. Details such as configuration information, device capabilities, and device identity can be advertised using this protocol.
LLDP advertises the following TLVs by default:
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DCBXP
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Management address
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Port description
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Port VLAN
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System capabilities
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System description
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System name
About DCBXP
The Data Center Bridging Exchange Protocol (DCBXP) is an extension of LLDP. It is used to announce, exchange, and negotiate node parameters between peers. DCBXP parameters are packaged as DCBXP TLVs in the LLDP packet. If CEE is used, DCBXP will use an acknowledgment mechanism over LLDP. When the port comes up, DCBX TLVs are sent and any DCBX TLVs received are processed. By default, the DCBX protocol is set to auto-detect, and the latest protocol version supported by both the peers is used.
Features that need to exchange and negotiate parameters with peer nodes using DCBXP are as follows:
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Priority-based Flow Control (PFC)—PFC is an enhancement to the existing Pause mechanism in Ethernet. It enables Pause based on user priorities or classes of service. A physical link that is divided into eight virtual links with PFC provides the capability to use Pause on a single virtual link without affecting traffic on the other virtual links. Enabling Pause on a per-user-priority basis allows administrators to create lossless links for traffic requiring no-drop service while retaining packet-drop congestion management for IP traffic.
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Enhanced Transmission Selection (ETS)—ETS enables optimal bandwidth management of virtual links. ETS is also called priority grouping. It enables differentiated treatments within the same priority classes of PFC. ETS provides prioritized processing based on bandwidth allocation, low latency, or best effort, resulting in per-group traffic class allocation. For example, an Ethernet class of traffic may have a high-priority designation and a best effort within that same class. ETS allows differentiation between traffic of the same priority class, thus creating priority groups.
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Application Priority Configuration—Carries information about the priorities that are assigned to specific protocols.
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Priority to DSCP Mapping—The mapping of the DSCP and COS values configured in the QoS policy are sent in the Application Priority TLV.
Note |
For information on the quality of service (QoS) features, see the Cisco Nexus 9000 Series NX-OS Quality of Service Configuration Guide. |
DCBXP is enabled by default, provided LLDP is enabled. When LLDP is enabled, DCBXP can be enabled or disabled using the [no] lldp tlv-select dcbxp command. DCBXP is disabled on ports where LLDP transmit or receive is disabled.
Beginning with Cisco NX-OS Release 10.2(3)F, an additional command is introduced: [no] lldp tlv-select dcbxp egress-queuing. While the [no] lldp tlv-select dcbxp command sends input queuing parameters in the ETS information that is exchanged with the peer, the [no] lldp tlv-select dcbxp egress-queuing command sends output queuing parameters in the ETS information. Hence, the bandwidths and priority information are extracted from the output queuing policy and exchanged with the peer.
At a time, you can configure either egress queuing or ingress queuing by running either lldp tlv-select dcbxp egress-queuing or lldp tlv-select dcbxp command as they overwrite each other.
The no forms of both the commands stop the DCBXP exchange on all interfaces.
To view which of the above two commands is enabled, run the show lldp tlv-select command.
When the default input queuing policy at system level is detached, the DCBXP exchange on all interfaces will stop sending ETS configuration and recommendation TLVs. However, the default output queuing policy at the system level cannot be detached.
High Availability
The LLDP feature supports stateless and stateful restarts. After a reboot or supervisor switchover, the running configuration is applied.
For more information on high availability, see the Cisco Nexus 9000 Series NX-OS High Availability and Redundancy Guide.
Virtualization Support
One instance of LLDP is supported.