Cisco Certified Network Associate (CCNA) 200-301 · Free study guide

Objective 2.4 — Configure LACP EtherChannel

EtherChannel combines compatible physical links into one logical interface. The switching or routing system treats the port-channel as a unit, while a hashing method distributes flows across active members. One flow is not normally striped packet by packet over every link.

LACP negotiation

Link Aggregation Control Protocol is the standards-based negotiation method in the CCNA scope. Active mode sends LACP messages; passive waits. Active- active and active-passive can form. Passive-passive does not initiate a bundle. The channel group number is locally significant and does not need to match the neighbor's number, though consistent documentation helps.

Do not mix LACP with static “on” behavior and expect negotiation. Both ends need compatible methods.

Layer 2 port channels

Layer 2 members must agree on relevant switchport parameters such as access or trunk mode, access VLAN, native VLAN, and allowed VLANs. Apply common policy to the logical port-channel where supported so members inherit a consistent design. Spanning tree sees the port-channel as one logical path, preventing individual members from being blocked as separate parallel links.

Layer 3 port channels

For a Layer 3 EtherChannel, convert members and the logical port-channel to routed operation consistently, then put the IP address on the port-channel rather than on individual members. Routing peers use the logical interface. Member physical state still affects total capacity.

Compatibility and suspension

Speed, duplex, Layer 2/Layer 3 mode, and switchport settings must be compatible. Platforms may suspend or leave a member standalone when it disagrees. A port- channel can be up with fewer active links than intended, so verify every member flag, not only the logical state.

IOS command map

For a two-link LACP lab bundle, select the members with interface range GigabitEthernet0/1 - 2, make their Layer 2 settings consistent, and apply channel-group 1 mode active. Configure shared trunk or access policy on interface Port-channel1 as the platform design requires. The peer may use a different local channel-group number, but it must use compatible LACP and link settings.

For a Layer 3 port channel, apply no switchport consistently and place the ip address on interface Port-channel1, not on individual members. Use show etherchannel summary to read protocol and member flags, show lacp neighbor to confirm the peer, and show interfaces Port-channel1 plus the relevant switchport or routing view to verify the logical interface. A bundle that is up with one suspended member is still degraded.

Worked scenario

Two trunk links should form an LACP bundle. One side is active on both; the other has one passive member and one member configured with a different native VLAN. The compatible link can join while the inconsistent link is suspended. Align the member's trunk policy through the logical design, then verify both links are bundled and the required VLANs cross the port-channel.

Verification evidence

Inspect channel summary, protocol, member flags, logical interface state, switchport or routed mode, and traffic counters. Confirm the neighbor's view. Test failure by removing one member only in an authorized lab or maintenance window, then verify the bundle remains and capacity changes as expected.

Common traps

• Configuring passive on both ends.
• Putting IP addresses on Layer 3 members.
• Applying inconsistent trunk settings to Layer 2 members.
• Assuming one flow uses every link simultaneously.
• Checking only that the port-channel is up.

Readiness checklist

• I can predict which LACP mode pairs form.
• I can build Layer 2 and Layer 3 port channels.
• I can identify member incompatibility.
• I verify each member and the logical interface.