lldp receive
Enables LLDP reception on an interface, allowing the device to receive LLDP advertisements from neighboring devices for network discovery and topology mapping.
Definition: lldp receive is a Cisco IOS interface config command. Enables LLDP reception on an interface, allowing the device to receive LLDP advertisements from neighboring devices for network discovery and topology mapping.
Overview
The `lldp receive` command, issued in interface configuration mode, enables the reception of Link Layer Discovery Protocol (LLDP) advertisements on a specific Cisco IOS interface. LLDP is a vendor-neutral, IEEE 802.1AB standard protocol that allows network devices to advertise their identity, capabilities, and neighbors on an Ethernet network. By enabling LLDP reception, the device listens for LLDP frames from directly connected neighbors, populating the local LLDP neighbor database.
This information is critical for network discovery, topology mapping, and inventory management, especially in multi-vendor environments where Cisco Discovery Protocol (CDP) is not supported. The command is typically used in conjunction with `lldp transmit` to enable full LLDP operation, though it can be enabled independently if only neighbor discovery is needed. Network engineers reach for this command when they need to discover adjacent devices, verify physical connectivity, or build an accurate network topology diagram.
It is an alternative to CDP, which is Cisco proprietary, and is essential when integrating non-Cisco switches, routers, or access points. In the broader workflow, enabling LLDP reception is often one of the first steps in network discovery, followed by verification with `show lldp neighbors`. The command takes effect immediately and is saved to the running configuration; it does not require a reload.
LLDP operates at Layer 2, using multicast address 01:80:c2:00:00:0e, and advertisements are sent periodically (default 30 seconds) with a hold time multiplier (default 4). The command is available in privileged EXEC mode (enable) and requires global `lldp run` to be enabled first. Important IOS behavior: LLDP is disabled by default on most Cisco IOS platforms; it must be enabled globally with `lldp run` before interface-level commands take effect.
The `lldp receive` command can be used on physical interfaces, subinterfaces, and port-channel interfaces. It does not impact routing or forwarding directly but provides valuable operational data for network management systems (NMS) and troubleshooting connectivity issues. Understanding LLDP and its configuration is a core skill for CCNA and CCNP candidates, as it appears in exam topics related to network access, IP connectivity, and automation.
lldp receiveWhen to Use This Command
- Enable LLDP receive on an access port to discover connected IP phones or switches.
- Configure LLDP receive on a trunk port to learn about neighboring switch capabilities and VLAN information.
- Enable LLDP receive on a router interface to discover directly connected routers for OSPF neighbor verification.
- Use with 'lldp transmit' to enable full LLDP operation for network monitoring tools.
Command Examples
Enable LLDP receive on an interface
interface GigabitEthernet0/1
lldp receiveRouter(config-if)# lldp receive Router(config-if)#
The command is entered in interface configuration mode. No output is shown if successful; the prompt returns without error.
Verify LLDP receive status on an interface
show lldp interface GigabitEthernet0/1GigabitEthernet0/1: Tx: enabled Rx: enabled Tx state: IDLE Rx state: WAIT_FOR_FRAME
The output shows LLDP transmit and receive status. 'Rx: enabled' confirms LLDP receive is active. 'Rx state: WAIT_FRAME' indicates the interface is listening for LLDP frames.
Understanding the Output
The 'lldp receive' command itself produces no output on success. To verify, use 'show lldp interface [interface]'. The key field is 'Rx: enabled' which confirms LLDP reception is active.
'Rx state' shows the current state of the LLDP receive process: 'WAIT_FOR_FRAME' means it is listening, 'FRAME_RECEIVED' means a frame was just received, and 'IDLE' may indicate no activity. If 'Rx: disabled' appears, LLDP receive is not enabled. In a real network, ensure both Tx and Rx are enabled for full LLDP operation.
Use 'show lldp neighbors' to see discovered devices; if none appear, check that LLDP receive is enabled on the interface and that the neighbor also has LLDP enabled.
Configuration Scenarios
Enable LLDP Reception on an Interface Connecting to a Third-Party Switch
A network engineer needs to discover a non-Cisco switch connected to GigabitEthernet0/1. CDP is not supported on the third-party device, so LLDP must be enabled to receive neighbor advertisements.
Topology
R1(Gi0/1)---192.168.1.0/30---(Gi0/1)ThirdPartySwitchSteps
- 1.Step 1: Enter global configuration mode: configure terminal
- 2.Step 2: Enable LLDP globally: lldp run
- 3.Step 3: Enter interface configuration mode for Gi0/1: interface GigabitEthernet0/1
- 4.Step 4: Enable LLDP reception: lldp receive
- 5.Step 5: Exit configuration mode and verify: end, then show lldp neighbors
! Enable LLDP globally lldp run ! interface GigabitEthernet0/1 lldp receive !
Verify: Use `show lldp neighbors` to verify. Expected output shows the third-party switch in the neighbor table with its interface, hold time, and capabilities.
Watch out: LLDP must be enabled globally with `lldp run` before interface-level commands take effect. If `lldp receive` is configured but `lldp run` is missing, the command will be accepted but LLDP will not operate.
Disable LLDP Transmission While Keeping Reception on a Management Interface
On a core switch, the management interface (VLAN 1 SVI) should only receive LLDP advertisements for monitoring purposes, but should not advertise itself to avoid cluttering neighbor tables of upstream devices.
Topology
CoreSwitch(Vlan1)---10.0.0.0/24---(Gi0/0)MgmtSwitchSteps
- 1.Step 1: Enter global configuration mode: configure terminal
- 2.Step 2: Enable LLDP globally: lldp run
- 3.Step 3: Enter interface configuration mode for the SVI: interface Vlan1
- 4.Step 4: Enable LLDP reception only: lldp receive
- 5.Step 5: Disable LLDP transmission: no lldp transmit
- 6.Step 6: Exit and verify: end, then show lldp interface Vlan1
! Enable LLDP globally lldp run ! interface Vlan1 lldp receive no lldp transmit !
Verify: Use `show lldp interface Vlan1` to verify that LLDP reception is enabled and transmission is disabled. Expected output shows 'Tx: disabled' and 'Rx: enabled'.
Watch out: The `no lldp transmit` command is used to disable transmission; simply omitting `lldp transmit` does not disable it if LLDP is globally enabled. Always explicitly configure both directions as needed.
Troubleshooting with This Command
When troubleshooting LLDP reception issues, the first step is to verify that LLDP is globally enabled using `show lldp`. If LLDP is not running, enable it with `lldp run`. Next, check the interface status with `show lldp interface [interface]`.
Healthy output should show 'LLDP: enabled' and 'Rx: enabled' for the interface. If Rx is disabled, the `lldp receive` command may be missing or overridden by a `no lldp receive` configuration. Also verify that the interface is not in a shutdown state and has a valid Layer 2 connection.
Use `show lldp neighbors` to see discovered devices. If no neighbors appear, check that the neighbor device is also sending LLDP advertisements. Common symptoms include: no neighbors listed, partial information (e.g., missing system name), or stale entries.
Stale entries indicate that the neighbor's hold timer expired, possibly due to link flapping or the neighbor stopping LLDP transmission. Focus on the 'Hold time' and 'Age' fields in `show lldp neighbors detail`. A high age relative to the hold time suggests the neighbor may be unreachable.
Also check the LLDP timer settings with `show lldp`; the default transmit interval is 30 seconds and hold multiplier is 4, giving a TTL of 120 seconds. If the neighbor is not seen, verify that the neighbor's LLDP is enabled and that no ACLs or port security features are blocking LLDP frames (destination MAC 01:80:c2:00:00:0e). Use `debug lldp packets` cautiously in a lab to see if LLDP frames are being received.
Correlate with `show interface` to ensure the interface is up/up and has no errors. For complex issues, compare the output of `show lldp neighbors` with `show cdp neighbors` to isolate whether the problem is LLDP-specific or a general connectivity issue. If LLDP works on some interfaces but not others, check for interface-specific configurations like `switchport mode access` or `switchport trunk allowed vlan` that might affect LLDP frame forwarding.
Remember that LLDP operates on the native VLAN for trunk ports; ensure the native VLAN is consistent across the link. Finally, if using LLDP with voice VLANs, verify that the voice VLAN is correctly configured and that LLDP is enabled on the voice VLAN interface.
CCNA Exam Tips
CCNA exam tip: LLDP is a vendor-neutral protocol; Cisco devices support both CDP and LLDP. Know that 'lldp receive' is an interface command.
CCNA exam tip: To enable LLDP globally, use 'lldp run' in global config. Without it, interface commands have no effect.
CCNA exam tip: LLDP and CDP can run simultaneously. The exam may test which protocol is used for specific scenarios (e.g., multi-vendor environments require LLDP).
CCNA exam tip: Remember that 'lldp receive' only enables reception; to send advertisements, also configure 'lldp transmit'.
Common Mistakes
Mistake 1: Enabling 'lldp receive' without first enabling 'lldp run' globally — the interface command will be accepted but LLDP will not operate.
Mistake 2: Forgetting to enable 'lldp transmit' when full LLDP operation is needed — the device will receive but not send advertisements.
Mistake 3: Applying 'lldp receive' on a Layer 3 interface without verifying that the interface is up/up — LLDP only works on active interfaces.
lldp receive vs lldp transmit
lldp receive and lldp transmit are per-interface commands used to control LLDP behavior. They are often confused because they are typically enabled together for full bidirectional LLDP operation, but each command independently controls one direction of LLDP traffic. Understanding the difference is crucial for troubleshooting neighbor discovery issues.
| Aspect | lldp receive | lldp transmit |
|---|---|---|
| Direction | Inbound (receive) | Outbound (transmit) |
| Effect on Neighbor Table | Populates neighbor entries | Does not populate neighbor table |
| Typical Use Case | Topology discovery from neighbors | Advertising local device info |
| Default State | Enabled if LLDP globally enabled | Enabled if LLDP globally enabled |
| Dependency | Requires global LLDP enable | Requires global LLDP enable |
Use lldp receive when you want the interface to learn about neighbors but not advertise itself, e.g., for passive monitoring.
Use lldp transmit when you want the interface to advertise its capabilities without learning about neighbors, e.g., on a server port.
Platform Notes
In IOS-XE (e.g., Catalyst 9000 series), the `lldp receive` command syntax is identical to classic IOS. However, IOS-XE may have additional LLDP features such as LLDP-MED (Media Endpoint Discovery) for VoIP devices. The output of `show lldp neighbors` is similar but may include additional fields like 'Network Policy' for LLDP-MED.
In NX-OS (e.g., Nexus switches), the equivalent command is `lldp receive` under interface configuration mode, but NX-OS uses a different global enable: `feature lldp` must be configured first. The NX-OS syntax for disabling transmission is `no lldp transmit`. For ASA firewalls, LLDP is not supported in classic ASA software; however, ASA with FirePOWER services (running a Linux-based system) may support LLDP on management interfaces.
In IOS-XR (e.g., ASR 9000), LLDP is enabled globally with `lldp` and interface-level commands are `lldp receive` and `lldp transmit`, similar to IOS. Note that IOS-XR uses a different configuration hierarchy (under `interface` sub-mode). For IOS versions prior to 12.2(33)SX, LLDP may not be available; it was introduced in later trains.
Always verify platform support with documentation. On some older IOS versions, the command `lldp receive` may not exist; instead, LLDP is controlled globally with `lldp run` and interface-level enable/disable is not supported. In such cases, LLDP is either enabled or disabled on all interfaces.
For CCNA/CCNP studies, focus on IOS 15.x and IOS-XE 16.x, which have consistent behavior.
Related Commands
lldp run
Globally enables Link Layer Discovery Protocol (LLDP) on the switch, allowing it to advertise and receive device information from directly connected LLDP-capable neighbors.
lldp transmit
Enables LLDP transmission on an interface, allowing the device to advertise its identity and capabilities to neighboring LLDP-enabled devices.
show lldp neighbors
Displays information about directly connected LLDP-capable devices, including device ID, local interface, hold time, capability, and port ID, used to verify LLDP neighbor discovery and troubleshoot Layer 2 connectivity.
Practice for the CCNA 200-301
Test your knowledge with practice questions covering all CCNA 200-301 exam domains.
Practice CCNA 200-301 Questions