Switch(config)# interface GigabitEthernet1\/0\/1\nSwitch(config-if)# no lldp transmit\nSwitch(config-if)# exit\n<\/code><\/pre>\nConversely, to completely disable LLDP processing on a security-sensitive port (e.g., public kiosks or DMZ demux links):<\/p>\n
Switch(config)# interface GigabitEthernet1\/0\/2\nSwitch(config-if)# no lldp transmit\nSwitch(config-if)# no lldp receive\nSwitch(config-if)# exit\n<\/code><\/pre>\nTo re-enable either capability on an interface:<\/p>\n
Switch(config)# interface range GigabitEthernet1\/0\/1 - 48\nSwitch(config-if-range)# lldp transmit\nSwitch(config-if-range)# lldp receive\nSwitch(config-if-range)# exit\n<\/code><\/pre>\n<\/span>Step 4: Fine-Tune Advertisement Timers (Optional)<\/span><\/h3>\nIn environments requiring faster discovery convergence or reduced multicast chatter, adjust the transmission interval, holdtime, and re-initialization delay:<\/p>\n
Switch(config)# lldp timer 15\nSwitch(config)# lldp holdtime 60\nSwitch(config)# lldp reinit 2\n<\/code><\/pre>\n\nlldp timer <seconds><\/code>: Frequency of periodic advertisements (default is 30 seconds).<\/li>\nlldp holdtime <seconds><\/code>: Duration the receiving device should retain information before discarding it (default is 120 seconds).<\/li>\nlldp reinit <seconds><\/code>: Delay before re-sending initialization packets on an interface after a link bounce (default is 2 seconds).<\/li>\n<\/ul>\n
\n<\/span>Configuring LLDP-MED for VoIP and IP Endpoint Discovery<\/span><\/h2>\nLLDP Media Endpoint Discovery (LLDP-MED), defined under ANSI\/TIA-1057, extends base LLDP capabilities to facilitate automated provisioning between network switches and media endpoints such as IP phones, conference systems, and video codecs. LLDP-MED communicates Voice VLAN IDs, Differentiated Services Code Point (DSCP) priorities, 802.1p Class of Service (CoS) tags, and fine-grained Power over Ethernet (PoE) demands.<\/p>\n
<\/span>Step 1: Define a Voice Network-Policy Profile<\/span><\/h3>\nLLDP-MED requires a defined network policy profile that packages the operational parameters of the real-time application.<\/p>\n
Switch(config)# network-policy profile 100 voice\nSwitch(config-network-policy)# voice vlan 150 cos 5\nSwitch(config-network-policy)# voice-signaling vlan 150 cos 3\nSwitch(config-network-policy)# exit\n<\/code><\/pre>\n<\/span>Step 2: Assign the Network Policy to Edge Interfaces<\/span><\/h3>\nApply the policy profile to switchports serving third-party or dual-homed VoIP telephones. Ensure the interface is configured as an access port with access and voice VLAN assignments:<\/p>\n
Switch(config)# interface GigabitEthernet1\/0\/10\nSwitch(config-if)# switchport mode access\nSwitch(config-if)# switchport access vlan 10\nSwitch(config-if)# switchport voice vlan 150\nSwitch(config-if)# network-policy 100\n<\/code><\/pre>\n<\/span>Step 3: Enable LLDP-MED Specific TLVs and Power Negotiation<\/span><\/h3>\nCisco switches transmit inventory, capability, and power TLVs by default once LLDP is globally up. You can verify or explicitly instruct the interface to send advanced power-negotiation and inventory attributes:<\/p>\n
Switch(config-if)# lldp med-tlv-select inventory-management\nSwitch(config-if)# lldp med-tlv-select network-policy\nSwitch(config-if)# lldp med-tlv-select power-management\n<\/code><\/pre>\n<\/span>Step 4: Configure Fast-Start Discovery<\/span><\/h3>\nWhen an endpoint boots up, the standard 30-second transmission interval causes significant configuration delays. LLDP-MED Fast-Start accelerates this exchange by sending frames at rapid 1-second intervals upon link detection.<\/p>\n
Switch(config)# lldp med-fast-start-repeat-count 5\n<\/code><\/pre>\nThis forces the switch to broadcast five LLDP-MED packets immediately when the link state transitions to up, accelerating the endpoint’s address acquisition and VLAN assignment.<\/p>\n
\n<\/span>Enabling LLDP on Cisco Nexus Switches (NX-OS)<\/span><\/h2>\nCisco Nexus data center platforms (Nexus 3000, 7000, and 9000 running NX-OS) employ a modular control plane where services run in isolated processes. Unlike Catalyst IOS\/IOS-XE, LLDP must be enabled through the NX-OS feature<\/code> subsystem before configuration syntax becomes available.<\/p>\n<\/span>Step 1: Enable the LLDP Feature Subsystem<\/span><\/h3>\nEnter configuration mode and initialize the process:<\/p>\n
switch# configure terminal\nswitch(config)# feature lldp\n<\/code><\/pre>\nTo confirm the process is active:<\/p>\n
switch(config)# show feature | grep lldp\nlldp 1 enabled\n<\/code><\/pre>\n<\/span>Step 2: Configure Interface Transmit and Receive Flags<\/span><\/h3>\nIn NX-OS, enabling feature lldp<\/code> activates the protocol across all supported Ethernet and fabric interfaces by default. To disable or customize on specific downlinks:<\/p>\nswitch(config)# interface Ethernet1\/1\nswitch(config-if)# no lldp transmit\nswitch(config-if)# no lldp receive\n<\/code><\/pre>\nTo adjust global NX-OS transmission intervals:<\/p>\n
switch(config)# lldp timer 30\nswitch(config)# lldp holdtime 120\n<\/code><\/pre>\n<\/span>Key Differences Between IOS-XE and NX-OS<\/span><\/h3>\n\n- Activation Command<\/strong>: IOS-XE uses
lldp run<\/code>, whereas NX-OS uses feature lldp<\/code>.<\/li>\n- Subsystem Architecture<\/strong>: Disabling the feature on NX-OS (
no feature lldp<\/code>) completely tears down the daemon and flushes runtime memory, whereas no lldp run<\/code> on IOS-XE turns off frame processing while retaining interface-level command bindings.<\/li>\n- Data Center Bridging (DCBX)<\/strong>: NX-OS integrates DCBX over LLDP natively for Priority Flow Control (PFC) and Enhanced Transmission Selection (ETS) in Fibre Channel over Ethernet (FCoE) and RoCE environments.<\/li>\n<\/ol>\n
\n<\/span>How to Verify and Troubleshoot LLDP Discovery<\/span><\/h2>\nOnce activated, validating protocol operation and diagnosing discovery failures requires a systematic examination of global statistics, neighbor tables, and interface parameters.<\/p>\n
<\/span>Step 1: Verify Global Operational State<\/span><\/h3>\nCheck whether LLDP is actively processing packets and review configured timers:<\/p>\n
Switch# show lldp\nGlobal LLDP Information:\n Status: ACTIVE\n LLDP advertisements are sent every 30 seconds\n LLDP hold time advertised is 120 seconds\n LLDP interface reinitialisation delay is 2 seconds\n<\/code><\/pre>\nIf the status reads INACTIVE<\/code>, confirm that lldp run<\/code> (or feature lldp<\/code> on NX-OS) was issued in configuration mode.<\/p>\n<\/span>Step 2: Inspect Connected Neighbors<\/span><\/h3>\nDisplay a summary of all directly connected Layer 2 neighbors:<\/p>\n
Switch# show lldp neighbors\nCapability codes:\n (R) Router, (B) Bridge, (T) Telephone, (C) DOCSIS Cable Device\n (W) WLAN Access Point, (P) Repeater, (S) Station, (O) Other\n\nDevice ID Local Intf Hold-time Capability Port ID\nsw-dist-01.corp Gi1\/0\/24 118 B,R Gi0\/1\npoly-ccx500-4b21 Gi1\/0\/10 115 B,T 0004.f24b.2100\nsrv-kvm-02.infra Gi1\/0\/12 109 S eth0\n\nTotal entries displayed: 3\n<\/code><\/pre>\n<\/span>Step 3: Analyze Detailed Neighbor Parameters<\/span><\/h3>\nTo view the advertised IP management address, firmware revision, VLAN assignment, or PoE requirements of a specific peer, use the detail<\/code> modifier:<\/p>\nSwitch# show lldp neighbors GigabitEthernet1\/0\/10 detail\n------------------------------------------------\nLocal Interface: Gi1\/0\/10\nChassis id: 0004.f24b.2100\nPort id: 0004.f24b.2100\nPort Description: Poly CCX 500\nSystem Name: poly-ccx500-4b21\nSystem Description: Polycom CCX 500 Phone; UC Software 7.2.1\n\nTime remaining: 112 seconds\nSystem Capabilities: B,T\nEnabled Capabilities: B,T\nManagement Addresses:\n IP: 10.150.2.45\nAuto Negotiation - supported, enabled\nPhysical media capabilities:\n 1000baseT(FD)\n 100base-TX(FD)\nMedia Attachment Unit type: 30\nVlan ID: 150\n<\/code><\/pre>\n<\/span>Step 4: Isolate Discovery Failures<\/span><\/h3>\nIf a known physical link is established but no neighbor appears in the table:<\/p>\n
\n- Check Directional Flags<\/strong>: Run
show lldp interface <interface-id><\/code>. Ensure both TX: enabled<\/code> and RX: enabled<\/code> are displayed.<\/li>\n- Review Error Counters<\/strong>: Execute
show lldp errors<\/code>. Increments in Bad Packet Errors<\/code> or TLVs Discarded<\/code> indicate corrupted frames or unsupported vendor TLV lengths.<\/li>\n- Inspect Physical Port Type<\/strong>: LLDP frames carry EtherType
0x88CC<\/code>. Ensure the port is not an unsupported tunnel or encapsulated sub-interface that silently drops standard Layer 2 multicast control frames.<\/li>\n- Physical Layer Mismatches<\/strong>: Unidirectional fiber conditions or autonegotiation mismatches prevent bidirectional frame verification, blocking entry registration.<\/li>\n<\/ol>\n
\n<\/span>Baseline LLDP Deployment Configuration Templates<\/span><\/h2>\nFor automated deployments via script, configuration manager, or copy-paste implementation across fleet hardware, use the following standardized baselines.<\/p>\n
<\/span>Standard Cisco IOS \/ IOS-XE Switch Baseline<\/span><\/h3>\n! ==========================================\n! Standard Cisco IOS-XE Baseline LLDP Setup\n! ==========================================\nconfigure terminal\n!\n! Activate protocol globally\nlldp run\nlldp timer 30\nlldp holdtime 120\nlldp reinit 2\n!\n! Define Voice Network Policy for LLDP-MED\nnetwork-policy profile 1 voice\n voice vlan 100 cos 5\n voice-signaling vlan 100 cos 3\n!\n! Apply standard interface parameters\ninterface range GigabitEthernet1\/0\/1 - 48\n lldp transmit\n lldp receive\n network-policy 1\n exit\n!\nend\nwrite memory\n<\/code><\/pre>\n<\/span>Ansible Deployment Task (IOS-XE)<\/span><\/h3>\n