interface port-channel [id]
Creates or enters the configuration mode for an EtherChannel port-channel interface, used to bundle multiple physical Ethernet links into a single logical link for redundancy and increased bandwidth.
Definition: interface port-channel [id] is a Cisco IOS global config command. Creates or enters the configuration mode for an EtherChannel port-channel interface, used to bundle multiple physical Ethernet links into a single logical link for redundancy and increased bandwidth.
Overview
The `interface port-channel [id]` command is a fundamental building block for configuring EtherChannel on Cisco IOS devices. EtherChannel, also known as Link Aggregation, allows you to bundle multiple physical Ethernet links into a single logical link, providing increased bandwidth and redundancy. This command is used to create or enter the configuration mode for a specific port-channel interface, where you can assign IP addresses, configure VLAN trunking, or apply QoS policies.
The concept behind EtherChannel is to treat multiple physical links as one logical link, leveraging load balancing across the member links while providing fault tolerance: if one link fails, traffic is redistributed among the remaining links without interruption. You would reach for this command when you need to aggregate bandwidth between switches, routers, or between a switch and a server, especially in environments where link redundancy is critical. Alternatives include using individual interfaces without bundling, but that would not provide the same level of redundancy or bandwidth aggregation.
In a broader workflow, you typically first configure the physical interfaces with the `channel-group` command, then use `interface port-channel` to apply logical configurations. Important IOS behaviors: the port-channel interface must be created before or simultaneously with the channel-group assignment; the command is available in global configuration mode; changes take effect immediately and are written to the running configuration; there is no special privilege level beyond the standard 15 for configuration; and the port-channel interface will not appear in the running config until at least one physical member is assigned. This command is essential for CCNA and CCNP candidates as it appears in many real-world scenarios, from campus LAN design to data center networking.
interface port-channel [id]When to Use This Command
- Aggregating two or more trunk links between switches to increase uplink bandwidth and provide redundancy.
- Combining access ports connecting a server to a switch for higher throughput and fault tolerance.
- Configuring a Layer 3 EtherChannel between a router and a switch to provide a high-bandwidth routed link.
- Setting up a cross-stack EtherChannel across multiple switches in a stack for resilient connectivity.
Parameters
| Parameter | Syntax | Description |
|---|---|---|
| id | <1-4096> | The port-channel number, ranging from 1 to 4096. This number must be unique per device and is used to identify the logical interface. Common mistakes include using an ID that conflicts with an existing VLAN interface or exceeding the platform-specific maximum (some older platforms support only up to 64). |
Command Examples
Create and configure a Layer 2 EtherChannel interface
interface port-channel 1Switch(config)#interface port-channel 1 Switch(config-if)#
The command enters interface configuration mode for port-channel 1. If the interface does not exist, it is created. The prompt changes to (config-if)# indicating you are now configuring that logical interface.
Configure a Layer 3 EtherChannel with an IP address
interface port-channel 10
ip address 192.168.1.1 255.255.255.0
no shutdownSwitch(config)#interface port-channel 10 Switch(config-if)#ip address 192.168.1.1 255.255.255.0 Switch(config-if)#no shutdown Switch(config-if)#
After entering port-channel 10, an IP address is assigned to the logical interface, making it a routed port. The 'no shutdown' ensures the interface is administratively up. The output shows each command being accepted without error.
Understanding the Output
The output of 'interface port-channel [id]' is minimal: it simply changes the CLI prompt to indicate you are in interface configuration mode for that port-channel. There is no detailed output; the command is used to enter configuration context. To verify the EtherChannel, use 'show etherchannel summary' or 'show interfaces port-channel [id]'.
In those outputs, look for the port-channel status (up/down), the member ports, and the protocol (LACP or PAgP). A healthy EtherChannel shows all member ports in the same bundle and the port-channel interface in an up/up state. Watch for mismatched port speeds, duplex, or VLAN configurations which can cause the channel to fail.
Configuration Scenarios
Configure EtherChannel between two switches for trunking
Two switches, SW1 and SW2, are connected via four Gigabit Ethernet links. The goal is to bundle these links into a single logical trunk to increase bandwidth and provide redundancy.
Topology
SW1(Gi0/0-3)---(Gi0/0-3)SW2Steps
- 1.Step 1: Enter global configuration mode on SW1: configure terminal
- 2.Step 2: Create the port-channel interface: interface port-channel 1
- 3.Step 3: Configure the logical interface as a trunk: switchport mode trunk
- 4.Step 4: Exit back to global config: exit
- 5.Step 5: Configure each physical interface: interface range gigabitethernet 0/0-3
- 6.Step 6: Set the channel-group: channel-group 1 mode active
- 7.Step 7: Repeat steps 1-6 on SW2 with the same port-channel number.
! SW1 Configuration interface port-channel 1 switchport mode trunk ! interface range gigabitethernet 0/0-3 channel-group 1 mode active ! ! SW2 Configuration interface port-channel 1 switchport mode trunk ! interface range gigabitethernet 0/0-3 channel-group 1 mode active
Verify: Use 'show etherchannel summary' to verify the port-channel is up and all member links are in use. Expected output shows port-channel 1 (Po1) in layer 2 mode, with status SU (standby/up) and member ports Gi0/0-3 in the same bundle.
Watch out: Ensure both switches use the same EtherChannel protocol mode (e.g., LACP active) and that the physical interfaces are configured identically (same speed, duplex, VLAN settings). Mismatched configurations can cause the bundle to fail.
Configure routed EtherChannel between a router and a switch
A router (R1) and a switch (SW1) are connected via two Gigabit Ethernet links. The goal is to create a routed EtherChannel to provide a single logical routed link with higher bandwidth.
Topology
R1(Gi0/0-1)---(Gi0/0-1)SW1Steps
- 1.Step 1: On R1, enter global config: configure terminal
- 2.Step 2: Create the port-channel interface: interface port-channel 1
- 3.Step 3: Assign an IP address: ip address 10.0.0.1 255.255.255.252
- 4.Step 4: Exit and configure physical interfaces: interface range gigabitethernet 0/0-1
- 5.Step 5: Assign to channel-group: channel-group 1 mode active
- 6.Step 6: On SW1, configure the port-channel as a routed interface: no switchport
- 7.Step 7: Assign IP address: ip address 10.0.0.2 255.255.255.252
- 8.Step 8: Configure physical interfaces with channel-group.
! R1 Configuration interface port-channel 1 ip address 10.0.0.1 255.255.255.252 ! interface range gigabitethernet 0/0-1 channel-group 1 mode active ! ! SW1 Configuration interface port-channel 1 no switchport ip address 10.0.0.2 255.255.255.252 ! interface range gigabitethernet 0/0-1 channel-group 1 mode active
Verify: Use 'show interfaces port-channel 1' to verify the interface is up/up and has the correct IP address. Also use 'show etherchannel summary' to confirm the bundle is operational.
Watch out: On the switch, you must use 'no switchport' to make the port-channel a routed interface; otherwise, it will default to layer 2 mode and the IP address will be rejected.
Troubleshooting with This Command
When troubleshooting EtherChannel issues, the `interface port-channel` command itself is not directly used for diagnostics, but it is essential to verify the configuration of the logical interface. Healthy output from `show interfaces port-channel 1` shows the interface status as 'up, line protocol is up' and the bandwidth reflects the aggregate of member links. Problem indicators include the interface being 'down/down' or 'administratively down', which often indicates a misconfiguration or physical issue.
Key fields to focus on in `show etherchannel summary` are the 'Status' column: 'SU' means the port-channel is up and all member ports are in use; 'SD' indicates the bundle is down; 'P' means the port is bundled; 'I' means individual (not bundled). Common symptoms this command helps diagnose include: a port-channel not forming because of mismatched parameters (speed, duplex, VLAN allowed list), or member ports being in 'err-disabled' state due to spanning-tree or security violations. A step-by-step diagnostic flow: 1) Check physical interfaces with `show interfaces status` to ensure they are up/up. 2) Verify the channel-group configuration on each physical interface with `show running-config interface [interface]`. 3) Use `show etherchannel summary` to see the overall bundle status. 4) If the bundle is down, use `show etherchannel port-channel` to see detailed protocol information. 5) For LACP, use `show lacp neighbor` to verify the peer is exchanging LACP packets.
Correlate with `show spanning-tree` to ensure the port-channel is not being blocked. Also, use `show logging` to see any EtherChannel-related error messages. The `debug etherchannel` command can provide real-time information, but use with caution in production.
CCNA Exam Tips
CCNA exam tip: Remember that the port-channel number must match on both sides of the link for the EtherChannel to form.
CCNA exam tip: You must assign physical interfaces to the port-channel using 'channel-group [number] mode [active|passive|desirable|auto|on]' under each physical interface.
CCNA exam tip: The exam may test that all physical interfaces in the channel must have the same speed, duplex, and VLAN configuration (if Layer 2).
CCNA exam tip: For Layer 3 EtherChannels, you must issue 'no switchport' on the port-channel interface before assigning an IP address.
Common Mistakes
Mistake 1: Forgetting to assign physical interfaces to the port-channel with the 'channel-group' command, resulting in the port-channel being empty and down.
Mistake 2: Configuring the port-channel interface with an IP address without first using 'no switchport' on a Layer 3 switch, causing the IP to be rejected.
Mistake 3: Using inconsistent EtherChannel modes (e.g., one side set to 'active' and the other to 'desirable' with PAgP) leading to negotiation failure.
interface port-channel [id] vs channel-group [id] mode [mode]
Both commands are essential for configuring EtherChannel on Cisco IOS, yet they operate at different levels: 'interface port-channel' creates or enters the logical bundle interface, while 'channel-group' binds a physical interface to that bundle. They are often used together but serve distinct roles, leading to confusion among new engineers.
| Aspect | interface port-channel [id] | channel-group [id] mode [mode] |
|---|---|---|
| Scope | Logical bundle interface (port-channel) | Physical interface assignment to bundle |
| Configuration Mode | Global configuration mode | Interface configuration mode (physical port) |
| Persistence | Creates the logical interface; persists in running config | Associates physical port with bundle; removed if no matching port-channel exists |
| Precedence | Should be configured first; else auto-created with default parameters | Can auto-create port-channel if not present (depending on mode) |
| Typical Use | Configure bundle-level settings (e.g., trunking, IP address, STP) | Add member links to EtherChannel with specific PAgP or LACP mode |
Use interface port-channel [id] when you need to configure global parameters on the EtherChannel bundle, such as VLAN trunking, IP addressing, or spanning-tree settings.
Use channel-group [id] mode [mode] on a physical interface when you want to add that port to an EtherChannel bundle and define the channeling protocol mode (active, passive, or desirable).
Platform Notes
In IOS-XE (e.g., Catalyst 9000 series), the syntax is identical to classic IOS, but the output of `show etherchannel summary` may include additional fields like 'Protocol' and 'Flags'. The NX-OS equivalent command is `interface port-channel [id]` as well, but NX-OS uses a different configuration hierarchy: you must first create the port-channel with `interface port-channel [id]` and then assign member interfaces using `channel-group [id] mode [active|passive|on]` under each physical interface. On ASA firewalls, EtherChannel is supported but the command is `interface port-channel [id]` as well, though the ASA uses a different configuration mode (e.g., `interface port-channel1`).
For IOS-XR, the equivalent is `interface Bundle-Ether [id]`; the concept is similar but the command syntax differs significantly. Between IOS versions, the maximum number of port-channels has increased: 12.x supported up to 64, 15.x up to 128, and 16.x (IOS-XE) up to 512. The `interface port-channel` command exists in all IOS versions, but the `channel-group` command's mode options (auto, desirable, on, active, passive) vary: PAgP modes (auto/desirable) are only available on older IOS, while LACP modes (active/passive) are standard from IOS 12.2 onward.
Always check the platform documentation for specific limitations.
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.
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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