itnetworking
Search / GitHub Start with lab 1

PTL-0006 Switching

Configuring Layer 2 EtherChannel with LACP

Bundle multiple physical Ethernet links into a single logical channel using standard Link Aggregation Control Protocol (LACP) to increase bandwidth and provide link redundancy.

Level
Intermediate
Time
40 min
Packet Tracer
8.2+
Simulator
Tested in Packet Tracer
You configure
S1, S2
Last reviewed
On this page

FILES Packet Tracer topology

Download starter file

starter.pkt, 48 KB. Open it in Cisco Packet Tracer 8.2+. Install Packet Tracer.

Solution / reference file

The completed topology with every task configured. Try the lab first and use this to check your work or when you are stuck.

Download solution file

completed.pkt, 49 KB.

File checksums (SHA-256)
starter.pkt
1230da2a9b915522d956e4fa64fe85af5753de36f703a8bde64865c066a114fb
completed.pkt
ed9c34089b572f9d5e38cf6a9e6368bb3cf1e30247cc8cb278ba5debf75a4c0e

Part of BSIT Networking Curriculum Learning Path (step 12 of 56) and CCNA-Aligned Topical Study Path (step 15 of 56).

Category: switching · Difficulty: intermediate · Lab ID: PTL-0006 · Document: reviewed · Simulator: tested pass

In traditional Ethernet switching, connecting multiple parallel physical cables between two switches triggers the Spanning Tree Protocol (STP) to block all but one link to prevent Layer 2 bridging loops. While this provides fault tolerance, it wastes available bandwidth. EtherChannel solves this by bundling multiple physical Ethernet links into a single logical channel (Port-channel). STP views the bundle as a single link, allowing all member links to forward traffic simultaneously with automated load sharing and sub-second failover if an individual link fails.

Learning Objectives#

  • Explain the operational benefits and STP interaction of link aggregation using EtherChannel.
  • Identify the strict configuration prerequisites for bundling switchports into a channel group.
  • Configure IEEE 802.3ad / 802.1AX Link Aggregation Control Protocol (LACP) in active and passive negotiation modes.
  • Configure and manage an 802.1Q trunk on the virtual Port-channel logical interface.
  • Interpret the output of show etherchannel summary and analyze channel group flags.

Prerequisites#

  • Understanding of Layer 2 switching concepts, trunking (802.1Q), and Spanning Tree Protocol (STP).
  • Familiarity with configuring Cisco Catalyst switches via CLI.
  • Cisco Packet Tracer 8.0 or newer.

Topology#

PTL-0006 Topology Diagram
PTL-0006 Topology Diagram

The topology features two Cisco Catalyst 2960 switches connected via redundant FastEthernet links bundled into Port-channel 1 (Po1):

               ┌─────────── FastEthernet0/1 ───────────┐
[Switch S1] ───┤                                       ├─── [Switch S2]
   │           └─────────── FastEthernet0/2 ───────────┘          │
   │           ◄─── Bundled as Port-channel 1 (Po1) ───►          │
 Fa0/6                                                          Fa0/6
   │                                                              │
[PC-A] (192.168.1.1/24)                                        [PC-B] (192.168.1.2/24)
Device Name Model Interface Connected Device Neighbor Interface Cable Type
S1 Catalyst 2960-24TT FastEthernet0/1 Switch S2 FastEthernet0/1 Copper Cross-Over / Straight-Through
S1 Catalyst 2960-24TT FastEthernet0/2 Switch S2 FastEthernet0/2 Copper Cross-Over / Straight-Through
S1 Catalyst 2960-24TT FastEthernet0/6 PC-A FastEthernet0 Copper Straight-Through
S2 Catalyst 2960-24TT FastEthernet0/1 Switch S1 FastEthernet0/1 Copper Cross-Over / Straight-Through
S2 Catalyst 2960-24TT FastEthernet0/2 Switch S1 FastEthernet0/2 Copper Cross-Over / Straight-Through
S2 Catalyst 2960-24TT FastEthernet0/6 PC-B FastEthernet0 Copper Straight-Through

Addressing Table#

Device Interface IPv4 Address Subnet Mask Default Gateway Purpose
S1 VLAN 1 (SVI) 192.168.1.11 255.255.255.0 192.168.1.1 Switch 1 Management
S2 VLAN 1 (SVI) 192.168.1.12 255.255.255.0 192.168.1.1 Switch 2 Management
PC-A FastEthernet0 192.168.1.1 255.255.255.0 N/A Host A Access
PC-B FastEthernet0 192.168.1.2 255.255.255.0 N/A Host B Access

Lab Tasks#

  1. Place two Catalyst 2960 switches on the canvas and interconnect them on ports FastEthernet0/1 and FastEthernet0/2.
  2. Configure basic hostnames and management IP addresses on Switch S1 and S2.
  3. On both switches, select the physical interface range FastEthernet0/1 - 2 and assign them to channel group 1 using LACP active mode.
  4. Verify that Cisco IOS automatically spawns the logical interface Port-channel 1.
  5. Apply trunking configuration directly to the logical interface Port-channel 1.
  6. Inspect the bundled channel status using show etherchannel summary.
  7. Verify trunking across the bundle using show interfaces trunk.
  8. Simulate a link failure by shutting down FastEthernet0/1 and confirm that Port-channel 1 remains up using the remaining link.

Configuration Walkthrough#

Important

EtherChannel Member Port Prerequisites: All physical member interfaces in an EtherChannel bundle MUST have identical:

  • Speed and duplex settings.
  • Switchport mode (all access or all trunk).
  • Access VLAN (if access ports) or Native VLAN and Allowed VLAN list (if trunk ports). If any setting differs, Cisco IOS will suspend the mismatched port and exclude it from the bundle.

1. Switch S1 Configuration#

Connect to Switch S1 CLI:

Switch> enable
Switch# configure terminal
Switch(config)# hostname S1

! Configure Management SVI
S1(config)# interface vlan 1
S1(config-if)# ip address 192.168.1.11 255.255.255.0
S1(config-if)# no shutdown
S1(config-if)# exit

! Bundle Physical Interfaces into Channel-Group 1 using LACP
S1(config)# interface range FastEthernet0/1 - 2
S1(config-if-range)# switchport mode trunk
S1(config-if-range)# channel-group 1 mode active
S1(config-if-range)# exit

! Configure the Logical Port-channel Interface
S1(config)# interface Port-channel 1
S1(config-if)# switchport mode trunk
S1(config-if)# exit

S1(config)# end
S1# copy running-config startup-config

2. Switch S2 Configuration#

Connect to Switch S2 CLI:

Switch> enable
Switch# configure terminal
Switch(config)# hostname S2

! Configure Management SVI
S2(config)# interface vlan 1
S2(config-if)# ip address 192.168.1.12 255.255.255.0
S2(config-if)# no shutdown
S2(config-if)# exit

! Bundle Physical Interfaces into Channel-Group 1
! Using 'active' mode initiates LACP negotiation; 'passive' responds only.
S2(config)# interface range FastEthernet0/1 - 2
S2(config-if-range)# switchport mode trunk
S2(config-if-range)# channel-group 1 mode active
S2(config-if-range)# exit

! Configure the Logical Port-channel Interface
S2(config)# interface Port-channel 1
S2(config-if)# switchport mode trunk
S2(config-if)# exit

S2(config)# end
S2# copy running-config startup-config

Verification#

1. Inspect EtherChannel Summary#

S1# show etherchannel summary

(Sample expected output — illustrative):

Flags:  D - down        P - in port-channel
        I - stand-alone s - suspended
        H - Hot-standby (LACP only)
        R - Layer3      S - Layer2
        U - in use      f - failed to allocate aggregator

Group  Port-channel  Protocol    Ports
------+-------------+-----------+-----------------------------------------------
1      Po1(SU)         LACP      Fa0/1(P)    Fa0/2(P)

Note

Decoding the Output Flags:

  • Po1(SU):
    • S: Layer 2 switchport channel.
    • U: In Use (the logical Port-channel is actively operational).
  • Fa0/1(P) and Fa0/2(P):
    • P: Bundled in Port-channel (actively participating in LACP frame forwarding).
  • If you observe Po1(SD) (D = Down) or Fa0/1(I) (I = Stand-alone), a negotiation or speed/duplex mismatch has prevented bundling.

2. Verify Trunking on the Logical Interface#

S1# show interfaces trunk

(Sample expected output — illustrative):

Port        Mode             Encapsulation  Status        Native vlan
Po1         on               802.1q         trunking      1

Port        Vlans allowed on trunk
Po1         1-1005

Notice that trunking is active on Po1. Physical ports Fa0/1 and Fa0/2 are subsumed under the logical aggregator.

3. Verify End-to-End Switch Reachability#

From Switch S1, ping Switch S2's SVI:

S1# ping 192.168.1.12
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 192.168.1.12, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 1/2/4 ms

Shut down member port FastEthernet0/1 on S1:

S1(config)# interface FastEthernet0/1
S1(config-if)# shutdown
S1(config-if)# end

Re-run ping and check summary:

S1# ping 192.168.1.12
Success rate is 100 percent (5/5)
S1# show etherchannel summary

Notice Po1(SU) remains in use with Fa0/2(P) carrying all traffic without dropping the logical connection.

Troubleshooting#

  • Problem: show etherchannel summary shows Po1(SD) and member ports show (D) or (s).
    • Check 1: Ensure all member ports have identical duplex, speed, and switchport mode. A common mistake is configuring trunk on one physical interface while another is access.
    • Check 2: Verify that the channel group number matches on member interfaces.
  • Problem: Member ports show (I) (Individual/Stand-alone).
    • Check: (I) indicates that the local switch is trying to negotiate LACP, but the remote switch is not responding. Ensure the remote switch has matching channel-group 1 mode active (or passive), and that both ends are connected to the correct ports.
  • Problem: Spanning Tree blocks the Port-channel interface.
    • Check: Run show spanning-tree. STP should block at the logical Port-channel level only if a genuine multi-switch loop exists. If physical member ports appear individually in the spanning-tree output, EtherChannel bundling has failed.

Key Takeaways#

  • EtherChannel combines up to 8 active physical links into a single logical link, multiplying aggregate throughput and providing seamless link redundancy.
  • LACP (IEEE 802.3ad / 802.1AX) is an open industry-standard protocol; at least one side must be set to active mode for negotiation to succeed.
  • Configuration changes should be applied directly to the logical interface Port-channel 1 to ensure all member ports maintain identical parameters.
  • STP operates on the Port-channel interface as a unified whole, preventing unnecessary port blocking on parallel physical connections.

References#

  • Cisco Systems, Catalyst 2960 Switch Software Configuration Guide, Rel. 12.2(55)SE: Configuring EtherChannels (Accessed 2026-10-26).
  • IEEE, IEEE Standard for Local and Metropolitan Area Networks--Link Aggregation: IEEE 802.1AX-2020.

Files and Validation Status#

Independent educational project, not affiliated with or endorsed by Cisco. Lab passwords are provided for educational simulation purposes only.

Reference configurations

Final device configurations from the solution. Like the solution file, these give the answers away.

S1 S1.txt, 632 B 
! ==========================================
! Switch S1 Configuration
! Lab: Configuring Layer 2 EtherChannel with LACP (PTL-0006)
! ==========================================
enable
configure terminal
hostname S1

! Management Interface
interface vlan 1
 ip address 192.168.1.11 255.255.255.0
 no shutdown
 exit
ip default-gateway 192.168.1.1

! Bundle Physical Interfaces into Channel Group 1 (LACP Active)
interface range FastEthernet0/1 - 2
 switchport mode trunk
 channel-group 1 mode active
 exit

! Logical Port-channel Interface
interface Port-channel 1
 switchport mode trunk
 exit

end
copy running-config startup-config

Download S1.txt

S2 S2.txt, 632 B 
! ==========================================
! Switch S2 Configuration
! Lab: Configuring Layer 2 EtherChannel with LACP (PTL-0006)
! ==========================================
enable
configure terminal
hostname S2

! Management Interface
interface vlan 1
 ip address 192.168.1.12 255.255.255.0
 no shutdown
 exit
ip default-gateway 192.168.1.1

! Bundle Physical Interfaces into Channel Group 1 (LACP Active)
interface range FastEthernet0/1 - 2
 switchport mode trunk
 channel-group 1 mode active
 exit

! Logical Port-channel Interface
interface Port-channel 1
 switchport mode trunk
 exit

end
copy running-config startup-config

Download S2.txt

Verification guide

Device models, cabling, expected show output and negative tests for this lab: Verification & Packet Tracer Assembly Guide: PTL-0006.

  • Switching
  • EtherChannel
  • LACP
  • Spanning Tree
  • Cisco IOS

This page is generated from labs/switching/etherchannel-lacp/README.md in the repository. Corrections go there.

Search

Type at least two letters, for example OSPF, DHCP relay or VLAN.