lacp port-priority [value]
Sets the LACP port priority for an interface, which determines which ports become active in an LACP EtherChannel when the maximum number of allowed ports is reached.
Definition: lacp port-priority [value] is a Cisco IOS interface config command. Sets the LACP port priority for an interface, which determines which ports become active in an LACP EtherChannel when the maximum number of allowed ports is reached.
Overview
The `lacp port-priority` command is an interface-level configuration command used on Cisco IOS devices to set the Link Aggregation Control Protocol (LACP) port priority for a specific interface. LACP is an IEEE 802.3ad standard protocol that dynamically bundles multiple physical links into a single logical EtherChannel, providing increased bandwidth and redundancy. The port priority determines which ports are selected to become active in the EtherChannel when the number of ports exceeds the maximum allowed (typically 8 or 16, depending on the platform).
Lower numerical values indicate higher priority. This command is critical in scenarios where you need to control which links are preferred in a bundle, especially when connecting to devices that may have asymmetric port capabilities or when you want to ensure that certain high-bandwidth or critical links are always active. Without setting port priority, LACP uses default priorities (32768) and may select ports based on other factors like port number, which may not align with your design intent.
This command is typically used in conjunction with `channel-group` and `lacp system-priority` to fine-tune EtherChannel behavior. It fits into the broader network configuration workflow after you have decided to use LACP (rather than static EtherChannel or PAgP) and have identified the interfaces to be bundled. You would reach for this command when you need to influence which ports become active in a LACP EtherChannel, for example, to prefer 10 Gigabit Ethernet ports over 1 Gigabit Ethernet ports, or to ensure that ports connected to a critical server remain active.
The command is available in privileged EXEC mode (configure terminal) and requires at least privilege level 15. Changes take effect immediately and are written to the running configuration. It is important to note that the port priority is only relevant when the number of ports in the bundle exceeds the maximum allowed; otherwise, all ports are active.
Also, the priority is per-interface and is advertised to the LACP peer, so both sides must agree on the active ports based on the system and port priorities. A common mistake is setting the priority on the wrong interface or forgetting to apply it to all interfaces in the channel group. The command does not affect the running config until the interface is part of a channel group configured with LACP mode (active or passive).
lacp port-priority [value]When to Use This Command
- Controlling which ports are active in a 4-port EtherChannel when only 2 ports are allowed, ensuring critical links stay active.
- Prioritizing high-bandwidth or redundant links over lower-speed or less reliable links in a multi-switch LACP bundle.
- Ensuring specific ports (e.g., uplinks to core) are preferred over access ports in a mixed EtherChannel.
- Troubleshooting LACP negotiation by adjusting priority to force a specific port to become active.
Parameters
| Parameter | Syntax | Description |
|---|---|---|
| value | <0-65535> | Sets the LACP port priority. Valid values range from 0 to 65535. Lower values indicate higher priority. The default is 32768. Common mistake: using values outside the range or not understanding that the priority is compared with the peer's port priority; the lower value wins. |
Command Examples
Setting LACP port priority to 100 on an interface
interface GigabitEthernet0/1
lacp port-priority 100Switch(config-if)# lacp port-priority 100
Switch(config-if)# end
Switch# show lacp neighbor
Flags: S - Device is requesting Slow LACPDUs
F - Device is requesting Fast LACPDUs
A - Device is in Active mode P - Device is in Passive mode
Channel group 1 neighbors
Partner's information:
LACP port Admin Oper Port Port
Port Flags Priority Key Key Number State
Gi0/1 SA 100 0x1 0x1 0x101 0x3D
Gi0/2 SA 32768 0x1 0x1 0x102 0x3DThe 'lacp port-priority 100' command sets the priority to 100 (lower is better). In the 'show lacp neighbor' output, the 'LACP port Priority' column shows 100 for Gi0/1, indicating it has higher priority than the default 32768 on Gi0/2.
Verifying LACP port priority after configuration
show etherchannel 1 port-channelPort-channel: Po1 ------------- Age of the Port-channel = 00d:00h:05m:32s Logical slot/port = 1/1 Number of ports = 2 HotStandby port = null Passive port list = null Port state = Port-channel Ag-Inuse Protocol: LACP Ports: 2 Max = 2 Ports in the Port-channel: Index Load Port EC state No of bits ------+------+------+------------------+----------- 0 00 Gi0/1 Active 0 1 00 Gi0/2 Active 0 Time since last port bundled: 00d:00h:05m:30s Gi0/1 Time since last port Un-bundled: 00d:00h:00m:00s Never
The output shows the EtherChannel summary. Both ports are Active. If the maximum number of ports were set to 1, the port with lower LACP priority (Gi0/1) would remain active, and the other would become HotStandby.
Understanding the Output
The 'lacp port-priority' command itself does not produce output; it configures the interface. To verify the effect, use 'show lacp neighbor' or 'show etherchannel summary'. In 'show lacp neighbor', the 'LACP port Priority' column displays the configured priority (lower value = higher priority).
In 'show etherchannel summary', the 'EC state' column shows 'Active' for bundled ports; if a port is not bundled due to priority, it may show 'Hot-Stby' or 'Suspended'. A good configuration ensures critical ports have lower priority values (e.g., 100) than others (default 32768). Watch for ports that are unexpectedly not bundled; check their LACP priority and system priority.
Configuration Scenarios
Preferring 10 Gigabit Ethernet ports over 1 Gigabit Ethernet ports in a LACP EtherChannel
A data center switch has a LACP EtherChannel consisting of two 10G ports and two 1G ports. The maximum number of active ports is 2. The goal is to ensure the 10G ports are always active and the 1G ports are standby.
Topology
SW1(Gi1/0/1,Gi1/0/2)---10G links---(Gi1/0/1,Gi1/0/2)SW2
SW1(Gi1/0/3,Gi1/0/4)---1G links---(Gi1/0/3,Gi1/0/4)SW2Steps
- 1.Step 1: Enter global configuration mode: configure terminal
- 2.Step 2: Enter interface configuration for the first 10G port: interface GigabitEthernet1/0/1
- 3.Step 3: Set LACP port priority to a low value: lacp port-priority 100
- 4.Step 4: Add the interface to the channel group: channel-group 1 mode active
- 5.Step 5: Repeat for the second 10G port: interface GigabitEthernet1/0/2, lacp port-priority 100, channel-group 1 mode active
- 6.Step 6: For the 1G ports, set a higher priority: interface GigabitEthernet1/0/3, lacp port-priority 32768, channel-group 1 mode active
- 7.Step 7: Repeat for the second 1G port: interface GigabitEthernet1/0/4, lacp port-priority 32768, channel-group 1 mode active
! interface GigabitEthernet1/0/1 lacp port-priority 100 channel-group 1 mode active ! interface GigabitEthernet1/0/2 lacp port-priority 100 channel-group 1 mode active ! interface GigabitEthernet1/0/3 lacp port-priority 32768 channel-group 1 mode active ! interface GigabitEthernet1/0/4 lacp port-priority 32768 channel-group 1 mode active !
Verify: show etherchannel 1 port-channel Expected output: Port-channel1 is up, line protocol is up. Active ports: Gi1/0/1, Gi1/0/2. Standby ports: Gi1/0/3, Gi1/0/4.
Watch out: Ensure the maximum number of active ports is set appropriately (default is 8). If the max is higher than the number of ports, all ports will be active regardless of priority.
Ensuring a specific port remains active in a multi-switch LACP bundle with limited active ports
A network engineer needs to guarantee that a specific port connected to a critical server remains active in a LACP EtherChannel that has a maximum of 4 active ports out of 6 total. The server is connected to port Gi0/1.
Topology
SW1(Gi0/1)---server
SW1(Gi0/2-6)---other switchesSteps
- 1.Step 1: Enter global configuration mode: configure terminal
- 2.Step 2: Enter interface configuration for the critical port: interface GigabitEthernet0/1
- 3.Step 3: Set a very low port priority: lacp port-priority 1
- 4.Step 4: Add to channel group: channel-group 1 mode active
- 5.Step 5: For other ports, keep default priority or set higher: interface range GigabitEthernet0/2-6, lacp port-priority 32768, channel-group 1 mode active
! interface GigabitEthernet0/1 lacp port-priority 1 channel-group 1 mode active ! interface range GigabitEthernet0/2-6 lacp port-priority 32768 channel-group 1 mode active !
Verify: show lacp 1 internal Expected output: Port Gi0/1 shows port priority 1, state: active. Other ports show priority 32768.
Watch out: The LACP system priority also affects selection. If the peer switch has a lower system priority, its port priorities may override. Ensure both sides are configured consistently.
Troubleshooting with This Command
When troubleshooting LACP EtherChannel issues, the `lacp port-priority` command is not directly used for diagnosis, but understanding its effect is crucial. The primary show commands for troubleshooting are `show lacp [channel-group-number] internal` and `show lacp [channel-group-number] neighbor`. Healthy output for `show lacp internal` shows each port's state as 'active' or 'standby', with the port priority displayed.
Problem indicators include ports in 'down' or 'err-disabled' state, or ports that are expected to be active but are in standby. Focus on the 'Port State' column: '0x3c' or '0x3d' indicates active, while '0x7c' or '0x7d' indicates standby. Also check the 'Port Priority' field to ensure it matches your configuration.
Common symptoms this command helps diagnose include: a high-priority port not becoming active (check if the peer's port priority is lower, or if the system priority is lower on the peer), or unexpected standby ports (likely due to misconfigured priorities). A step-by-step diagnostic flow: 1) Verify the EtherChannel is up with `show etherchannel summary`. 2) Check the number of active ports with `show etherchannel port-channel`. 3) If fewer ports are active than expected, use `show lacp <channel> internal` to see each port's state and priority. 4) Compare the port priorities with the peer using `show lacp <channel> neighbor`. 5) If a port with higher priority (lower number) is standby, check the system priority on both sides with `show lacp sys-id`. The system with lower system priority wins; if equal, port priority is compared. 6) Also verify that the maximum number of active ports is not exceeded.
Correlate with `show interfaces` to check for physical errors or speed/duplex mismatches. The `debug lacp` command can provide real-time negotiation details, but use with caution in production. Remember that port priority only matters when the number of ports in the bundle exceeds the maximum allowed; if all ports are active, priority is irrelevant.
Also, changes to port priority take effect immediately, but the LACP negotiation may take a few seconds to re-elect active ports. If a port is stuck in standby, re-issue the `lacp port-priority` command with a lower value and verify with `clear lacp <channel> counters` to reset the negotiation.
CCNA Exam Tips
CCNA exam tip: LACP port priority is used to determine which ports become active when the maximum number of ports is reached; lower value = higher priority.
CCNA exam tip: The default LACP port priority is 32768; you can set it from 1 to 65535.
CCNA exam tip: LACP port priority is per-interface, while LACP system priority is global; both affect port selection.
CCNA exam tip: In the exam, you may be asked to configure LACP so that a specific port is preferred; use 'lacp port-priority' with a low value.
Common Mistakes
Mistake: Setting the priority too high (e.g., 65535) thinking it gives preference; actually lower is better.
Mistake: Forgetting to set the LACP system priority as well; port priority only matters if system priority is equal.
Mistake: Applying the command to the wrong interface or not verifying with 'show lacp neighbor'.
lacp port-priority [value] vs lacp system-priority [value]
These two LACP commands are commonly confused because both influence bundle negotiation but operate at different levels: lacp port-priority per interface determines which ports become active when the bundle is full, while lacp system-priority sets the global system ID priority to decide which switch controls the bundle.
| Aspect | lacp port-priority [value] | lacp system-priority [value] |
|---|---|---|
| Scope | Per-interface | Global (system-wide) |
| Configuration Mode | Interface configuration | Global configuration |
| Effect on LACP | Controls port selection within a bundle | Determines which switch is the system with higher priority |
| Persistence | Applied per interface, survives reload | Applied globally, persists across reboots |
| Precedence | Lower value means more likely to be active | Lower value means higher system priority |
| Typical Use | Ensure critical ports remain active in a bundle | Prevent ambiguity or split bundles between switches |
Use lacp port-priority [value] when you need to control which specific interfaces stay active in an EtherChannel if the number of eligible ports exceeds the maximum allowed.
Use lacp system-priority [value] when you need to designate which switch should control the LACP negotiation and bundle formation across multiple switches.
Platform Notes
In IOS-XE (e.g., Catalyst 9000 series), the `lacp port-priority` command syntax is identical to classic IOS. However, the output of `show lacp internal` may have slightly different formatting, but the key fields (port priority, state) remain. In NX-OS (e.g., Nexus switches), the equivalent command is `lacp port-priority <value>` under interface configuration mode, but note that NX-OS uses a different default priority (32768 as well) and the command is applied per interface.
The verification command on NX-OS is `show lacp interface ethernet <slot/port>`. On ASA firewalls, LACP is supported in transparent or routed mode, and the command is `lacp port-priority <value>` under interface configuration, but the ASA uses a different default (32768) and the maximum number of active ports is 8. In IOS-XR (e.g., ASR 9000), the command is `lacp port-priority <value>` under interface configuration, but note that IOS-XR uses a different LACP implementation and the command may be available only in certain releases.
For IOS versions, the command has been available since 12.2(33)SXH and later. In older IOS (12.x), the command may not exist; instead, use `port-priority` under the interface (without the 'lacp' keyword). In 15.x and 16.x, the syntax is consistent.
Always check the specific platform documentation, as some platforms may have a maximum port priority value of 65535, while others may limit to 255. Also, on some platforms, the port priority is only used when the system priority is equal; otherwise, system priority takes precedence.
Related Commands
channel-group [id] mode [mode]
Assigns an interface to an EtherChannel bundle with a specified channel-group number and mode (active, passive, or desirable) to aggregate multiple physical links into a single logical link for redundancy and increased bandwidth.
lacp system-priority [value]
Sets the LACP system priority to determine which switch controls the EtherChannel bundle when negotiating with a peer.
show etherchannel summary
Displays the status and configuration of all EtherChannel interfaces on the switch, used to verify channel bundling, port membership, and protocol state.
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