channel-group [id] mode [active|passive|on]
Assigns an interface to a port-channel and sets the LACP negotiation mode.
Overview
The 'channel-group' command on Cisco NX-OS (Nexus) is used to assign a physical Ethernet interface to a port-channel (also known as an EtherChannel). A port-channel aggregates multiple physical links into a single logical link, providing increased bandwidth and redundancy. The command specifies the port-channel ID and the LACP (Link Aggregation Control Protocol) mode: active, passive, or on. LACP is an IEEE standard (802.3ad) that allows dynamic negotiation and management of the aggregation. In active mode, the interface actively sends LACP packets to negotiate the channel. In passive mode, it responds to LACP packets but does not initiate. The 'on' mode creates a static port-channel without LACP, requiring manual configuration on both ends. This command is typically used in data center environments where high availability and bandwidth are critical, such as connecting switches to servers or inter-switch links. On Nexus platforms, the port-channel interface must exist (either pre-configured or auto-created) before adding members. The command is entered in interface configuration mode for each physical interface that will be part of the port-channel. Verification is done using 'show port-channel summary' to see the status of the port-channel and its members, and 'show lacp neighbor' to check LACP negotiation details. Troubleshooting involves checking for mismatched modes, speed/duplex mismatches, or physical layer issues. The command is fundamental for network engineers designing resilient and high-performance networks.
channel-group [id] mode [active|passive|on]When to Use This Command
- Aggregating multiple physical links between two switches for increased bandwidth and redundancy.
- Connecting a server with dual NICs to a Nexus switch using LACP for load balancing.
- Creating a static port-channel without LACP negotiation for compatibility with non-LACP devices.
- Configuring LACP active mode to initiate negotiation and form a dynamic port-channel.
Parameters
| Parameter | Syntax | Description |
|---|---|---|
| id | 1-4096 | The port-channel number. This must match the port-channel interface ID. On Nexus, the range is typically 1-4096. |
| mode | active | passive | on | Specifies the LACP negotiation mode. 'active' enables LACP and initiates negotiation. 'passive' enables LACP but waits for peer. 'on' forces the link into a static port-channel without LACP. |
Command Examples
Configure LACP Active on Ethernet1/1
interface ethernet1/1
channel-group 10 mode activeThis command configures interface Ethernet1/1 to be part of port-channel 10 with LACP active mode, meaning the interface will actively negotiate LACP with the peer.
Configure Static Port-Channel (mode on)
interface ethernet1/2
channel-group 20 mode onThis forces the interface into port-channel 20 without LACP negotiation, used when the peer does not support LACP.
Understanding the Output
The channel-group command itself does not produce output; verification is done via 'show port-channel summary' or 'show lacp neighbor'. In 'show port-channel summary', the output shows each port-channel with its member interfaces and status. Key fields include: Group (port-channel number), Port-Channel (interface name), Type (e.g., Eth for Ethernet), Protocol (LACP or none), Member Ports (list of interfaces), and Flags. Flags like 'P' indicate bundled (active) ports, 'D' indicates down, 'S' indicates suspended. Healthy values show all member ports as 'P' (bundled). Problem values include 'D' (down) or 'S' (suspended) indicating misconfiguration or link issues. 'show lacp neighbor' displays LACP details: neighbor system ID, port, and state. A healthy LACP session shows 'Bndl' (bundled) state; 'Ind' (individual) or 'Down' indicates problems.
Configuration Scenarios
LACP Active Port-Channel between Two Nexus Switches
Two Nexus switches are connected via two 10G interfaces. LACP is used for dynamic aggregation.
Topology
[Nexus-A] --- e1/1 --- [Nexus-B]
--- e1/2 ---Steps
- 1.On Nexus-A, create port-channel interface 1.
- 2.Configure interface e1/1 and e1/2 with channel-group 1 mode active.
- 3.On Nexus-B, create port-channel interface 1.
- 4.Configure corresponding interfaces with channel-group 1 mode active (or passive).
! Nexus-A interface port-channel1 no shutdown interface ethernet1/1 channel-group 1 mode active interface ethernet1/2 channel-group 1 mode active ! Nexus-B interface port-channel1 no shutdown interface ethernet1/1 channel-group 1 mode active interface ethernet1/2 channel-group 1 mode active
Verify: Use 'show port-channel summary' to verify both member ports are bundled (P). Use 'show lacp neighbor' to see LACP state.
Watch out: Ensure both sides use the same LACP mode (active-active or active-passive). If one side is passive and the other is passive, no negotiation occurs.
Static Port-Channel to a Non-LACP Server
A server with two NICs does not support LACP. A static port-channel is configured on the Nexus switch.
Topology
[Nexus] --- e1/1 --- [Server]
--- e1/2 ---Steps
- 1.On Nexus, create port-channel interface 10.
- 2.Configure interfaces e1/1 and e1/2 with channel-group 10 mode on.
- 3.On the server, configure the NICs in a static team (e.g., load balancing).
interface port-channel10 no shutdown interface ethernet1/1 channel-group 10 mode on interface ethernet1/2 channel-group 10 mode on
Verify: Use 'show port-channel summary' to see both ports bundled. No LACP neighbors will appear.
Watch out: Static mode requires identical configuration on both ends; any mismatch (e.g., speed) can cause issues without LACP to detect.
Troubleshooting with This Command
When troubleshooting port-channel issues on Nexus, start with 'show port-channel summary' to see the status of each member. Look for flags: 'P' (bundled) is good, 'D' (down) indicates link down, 'S' (suspended) means the port is not participating due to misconfiguration (e.g., speed/duplex mismatch, VLAN mismatch, or LACP mode mismatch). If LACP is used, 'show lacp neighbor' shows the peer's system ID and port state. A healthy LACP session shows 'Bndl' (bundled) for the port state; 'Ind' (individual) means the port is not aggregated, often due to mode mismatch. Check 'show interface' for physical errors. Common issues: one side configured as 'active' and the other as 'passive' works, but both 'passive' fails. Speed and duplex must match on all member links. On Nexus, ensure the port-channel interface itself is not shutdown. Also, verify that the allowed VLANs on the port-channel match the member interfaces. Use 'show port-channel database' for detailed member info. If a port is suspended, check 'show port-channel compatibility-parameters' to see why. For static mode, ensure both ends are configured identically; LACP is not available to detect mismatches. Finally, check for hardware limitations: some Nexus models have a maximum number of port-channels or members per port-channel.
CCNA Exam Tips
Remember that 'mode active' and 'mode passive' both use LACP, but only active initiates negotiation.
Static port-channels (mode on) do not use LACP and cannot detect mismatched configurations on the peer.
On Nexus, the port-channel interface must be created before or automatically when the first member is added.
Common Mistakes
Mixing LACP modes (active/passive) with static (on) on different sides of the same link causes the port-channel to fail.
Forgetting to create the port-channel interface before adding members (though Nexus auto-creates it, but best practice is to configure it explicitly).
Applying channel-group to a port that is already a member of another port-channel without removing it first.
Platform Notes
On Cisco NX-OS (Nexus), the 'channel-group' command behaves similarly to Cisco IOS, but there are key differences. In NX-OS, the port-channel interface is automatically created when the first member is added, but it is best practice to explicitly configure it. NX-OS supports up to 4096 port-channels (depending on model). The 'mode on' is equivalent to 'no lacp' in IOS. NX-OS also supports 'lacp rate' command to set fast or slow LACP rate. For vPC (Virtual Port Channel), the configuration is similar but requires additional steps. On other platforms like Arista, the equivalent command is 'channel-group <id> mode <active/passive/on>' as well. On Juniper, it's 'set interfaces aeX aggregated-ether-options lacp active' and 'set interfaces ge-0/0/0 ether-options 802.3ad aeX'. NX-OS version differences: older versions may have different default LACP rates. Always check the specific Nexus model documentation for maximum port-channel limits.
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