📘 CCNA 200-301 v1.1
2.4 Configure and Verify (Layer 2/Layer 3) EtherChannel (LACP)
1. What is EtherChannel?
EtherChannel is a technology that allows you to bundle multiple physical Ethernet links into one logical link.
This logical link is treated by switches or routers as a single interface.
Why EtherChannel is used
- To increase bandwidth between devices (for example, between two switches).
- To provide redundancy — if one physical link fails, traffic continues through other links.
- To simplify configuration — because multiple links are managed as one logical interface instead of separately.
2. How EtherChannel Works
When EtherChannel is configured, multiple physical interfaces are grouped together.
These interfaces:
- Must have the same speed and duplex settings.
- Must belong to the same VLAN (if it’s a Layer 2 EtherChannel).
- Are seen as a single logical interface called a Port Channel.
Port Channel Interface
When you configure EtherChannel, a new interface appears in the configuration, for example:
interface Port-channel1
All configuration (like VLAN, IP address, trunking, etc.) is done on this Port-channel interface, not on the individual physical interfaces.
3. EtherChannel Types (Based on Negotiation Protocol)
EtherChannel can be created using:
- PAgP (Port Aggregation Protocol) – Cisco proprietary.
- LACP (Link Aggregation Control Protocol) – IEEE standard (802.3ad).
For the CCNA 200-301 exam, focus on LACP, because it is vendor-neutral and works between Cisco and non-Cisco devices.
4. LACP (Link Aggregation Control Protocol)
What is LACP
- LACP is defined in IEEE 802.3ad standard.
- It is used to automatically form EtherChannel between devices.
- It negotiates which links can be active and ensures that both ends agree on the EtherChannel settings.
LACP Modes
Each interface participating in LACP can be configured in one of two modes:
| Mode | Description | Negotiates EtherChannel? |
|---|---|---|
| Active | Actively tries to form an EtherChannel by sending LACP packets. | Yes |
| Passive | Waits for the other side to start negotiation. | Yes (but only if the other side is Active) |
Important Rule:
- Active + Passive → EtherChannel forms
- Active + Active → EtherChannel forms
- Passive + Passive → No EtherChannel
5. Types of EtherChannel (Layer 2 vs Layer 3)
a) Layer 2 EtherChannel
- Used between switches.
- The Port-channel interface acts as a switchport.
- Can be configured as:
- Access Port (for a single VLAN)
- Trunk Port (to carry multiple VLANs)
Example
Between two switches connecting VLAN traffic.
Switch1 --- EtherChannel --- Switch2
b) Layer 3 EtherChannel
- Used between routers or Layer 3 switches.
- The Port-channel interface is configured as a routed port (not a switchport).
- It can have an IP address assigned.
Example
Used between two Layer 3 devices (like multilayer switches) to route IP traffic.
interface Port-channel1
no switchport
ip address 10.1.1.1 255.255.255.0
6. Requirements for EtherChannel Configuration
All physical interfaces must have matching settings:
- Same speed and duplex.
- Same VLAN membership (for Layer 2).
- Same trunking mode (either all access or all trunk).
- Same allowed VLANs (if trunk).
- No SPAN (port mirroring) or routed configuration on the physical ports.
- Interfaces must not be in shutdown mode.
If these settings don’t match, the EtherChannel will fail to form.
7. LACP Configuration Steps (Layer 2 Example)
Here’s how to configure Layer 2 LACP EtherChannel between two switches.
Step 1: Select interfaces
Switch(config)# interface range gigabitEthernet0/1 - 2
Step 2: Set switchport mode
Switch(config-if-range)# switchport mode trunk
Step 3: Configure EtherChannel with LACP
Switch(config-if-range)# channel-group 1 mode active
This creates Port-channel1 using LACP in active mode.
Step 4: Verify Port-channel
Switch# show etherchannel summary
You should see something like:
Group Port-channel Protocol Ports
------+-------------+----------+-------------------------
1 Po1(SU) LACP Gi0/1(P) Gi0/2(P)
Meaning of Flags
- S – Layer 2 (Switch)
- U – In use
- P – Port is bundled in the channel
- D – Down
8. LACP Configuration (Layer 3 Example)
If you want to make a Layer 3 EtherChannel, follow these steps:
Switch(config)# interface range gigabitEthernet0/1 - 2
Switch(config-if-range)# no switchport
Switch(config-if-range)# channel-group 1 mode active
Switch(config)# interface port-channel1
Switch(config-if)# no switchport
Switch(config-if)# ip address 10.1.1.1 255.255.255.0
Verify using:
Switch# show etherchannel summary
Switch# show ip interface brief
9. Verification Commands
1. show etherchannel summary
- Displays EtherChannel groups, protocol, and status.
2. show interfaces port-channel
- Displays details of the Port-channel interface.
3. show running-config
- Displays configuration of EtherChannel.
4. show spanning-tree interface port-channel
- Shows how EtherChannel participates in Spanning Tree.
5. show interfaces etherchannel
- Displays load-balancing and operational details.
10. Load Balancing in EtherChannel
EtherChannel can distribute traffic among member links.
Load balancing is based on hash algorithms, such as:
- Source MAC address
- Destination MAC address
- Source and destination IP address
- Source and destination port numbers (for Layer 4 traffic)
You can check the load balancing method with:
Switch# show etherchannel load-balance
You can change it with:
Switch(config)# port-channel load-balance src-dst-ip
11. Troubleshooting EtherChannel
If EtherChannel doesn’t form:
- Check mode compatibility (Active + Passive or Active + Active).
- Ensure same configurations (speed, duplex, VLAN, trunk mode).
- Use
show etherchannel summaryandshow interfaces statusto verify.
12. Summary Table
| Type | Layer | Command Example | IP Address | Notes |
|---|---|---|---|---|
| Layer 2 EtherChannel | Data Link (Switchport) | switchport mode trunkchannel-group 1 mode active | No | Used between switches |
| Layer 3 EtherChannel | Network (Routed Port) | no switchportchannel-group 1 mode active | Yes | Used between routers or multilayer switches |
13. Key Points to Remember for the Exam
✅ EtherChannel combines multiple links into one logical connection.
✅ LACP is IEEE 802.3ad standard; uses Active and Passive modes.
✅ Active + Passive or Active + Active = EtherChannel forms.
✅ All physical interfaces must have identical settings.
✅ Verify using show etherchannel summary.
✅ Can be configured as Layer 2 (switchport) or Layer 3 (routed).
✅ Increases bandwidth and provides redundancy.
