> ## Content Index > Fetch the complete content index at: https://www.pinglabz.com/llms.txt > Use this file to discover other available public pages before exploring further. # Configuring EtherChannel with LACP on Cisco Catalyst Switches - URL: https://www.pinglabz.com/configure-lacp-etherchannel-cisco-ios/ - Published: 2025-10-22T21:13:45.000Z - Updated: 2026-07-04T23:01:37.000Z - Description: LACP bundles multiple physical links into one logical pipe—doubling or quadrupling bandwidth while keeping STP happy and providing automatic failover. - Author: Jaime - Tags: VLAN, #Import 2026-08-01 19:54 ## Why Link Aggregation Matters A 10 Gbps uplink between DIST-SW1 and CORE-SW1 runs at capacity. Add another 10 Gbps port - you've just doubled bandwidth and eliminated a single point of failure. But the switch won't automatically load-balance across both ports. EtherChannel bundles them into a single logical link that Spanning Tree sees as one interface, meaning no blocked ports and full utilization of both paths. (This article is part of the PingLabz VLAN series - the [full VLAN and Layer 2 switching guide](https://www.pinglabz.com/vlans-layer-2-switching/) maps the whole cluster in reading order.) LACP (Link Aggregation Control Protocol, IEEE 802.3ad) negotiates the bundle dynamically, ensuring both sides agree before traffic flows. It's the industry standard and far superior to Cisco's legacy PAgP protocol. ## LACP Fundamentals - **EtherChannel**: A logical aggregation of physical links, presented to the OS as a single `port-channel` interface. - **LACP**: The protocol (802.3ad) that dynamically negotiates bundle membership. - **LACP Modes**: - `active`: Initiates LACP negotiation. The port actively sends LACP PDUs. - `passive`: Responds to LACP negotiation but doesn't initiate. Use only if the far end is `active`. - `on`: Static bundling (no protocol). Both sides must have identical port lists. Best practice: **Use `active` on both sides** or `active` on one side and `passive` on the other. ## Configuration: Po1 Between DIST-SW1 and CORE-SW1 We'll bundle ports Gi1/0/1 and Gi1/0/2 between DIST-SW1 (10.0.0.2) and CORE-SW1 (10.0.0.1). Both switches run Catalyst 9000 series. ### DIST-SW1 Configuration ``` DIST-SW1# configure terminal DIST-SW1(config)# interface range GigabitEthernet1/0/1 - 2 DIST-SW1(config-if-range)# no shutdown DIST-SW1(config-if-range)# speed 10000 DIST-SW1(config-if-range)# duplex full DIST-SW1(config-if-range)# channel-group 1 mode active DIST-SW1(config-if-range)# exit ``` The `channel-group 1 mode active` command assigns both ports to channel group 1 using LACP active mode. The switch automatically creates `Port-Channel 1`. ### Configure the Port-Channel Interface ``` DIST-SW1(config)# interface Port-Channel 1 DIST-SW1(config-if)# description Link to CORE-SW1 DIST-SW1(config-if)# mtu 1500 DIST-SW1(config-if)# no shutdown DIST-SW1(config-if)# end ``` The Port-Channel interface is where you apply higher-level config (trunk mode, VLAN membership, etc.). ### CORE-SW1 Configuration (Mirror of DIST-SW1) ``` CORE-SW1# configure terminal CORE-SW1(config)# interface range GigabitEthernet1/0/1 - 2 CORE-SW1(config-if-range)# no shutdown CORE-SW1(config-if-range)# speed 10000 CORE-SW1(config-if-range)# duplex full CORE-SW1(config-if-range)# channel-group 1 mode active CORE-SW1(config-if-range)# exit CORE-SW1(config)# interface Port-Channel 1 CORE-SW1(config-if)# description Link to DIST-SW1 CORE-SW1(config-if)# mtu 1500 CORE-SW1(config-if)# no shutdown CORE-SW1(config-if)# end ``` ### Make Po1 a Trunk (if carrying multiple VLANs) If Po1 carries VLANs 10, 20, 30, 40, 99, 100: ``` DIST-SW1(config)# interface Port-Channel 1 DIST-SW1(config-if)# switchport trunk encapsulation dot1q DIST-SW1(config-if)# switchport mode trunk DIST-SW1(config-if)# switchport trunk allowed vlan 10,20,30,40,99,100 DIST-SW1(config-if)# switchport trunk native vlan 99 DIST-SW1(config-if)# end ``` Repeat on CORE-SW1. ### Load-Balancing Configuration By default, EtherChannel uses source MAC address hashing. For better distribution, especially in core-to-core links, use source and destination MAC: ``` DIST-SW1# configure terminal DIST-SW1(config)# port-channel load-balance src-dst-mac DIST-SW1(config)# end ``` Other options: - `src-mac`: Source MAC only. - `dst-mac`: Destination MAC only. - `src-ip`: Source IP address. - `dst-ip`: Destination IP address. - `src-dst-ip`: Source and destination IP (best for most environments). - `src-port`: TCP/UDP source port. - `dst-port`: TCP/UDP destination port. For data center and campus uplinks, `src-dst-ip` often provides the best balance. ## Verification Commands ### Show EtherChannel Summary ``` DIST-SW1# show etherchannel summary Flags: D - down P - bundled in port-channel I - stand-alone p - bundled in port-channel (inactive) H - Hot-standby (LACP only) R - Layer3 S - Layer2 U - in use f - failed to allocate aggregator Number of channel-groups in use: 1 Number of aggregators: 1 Group Port-channel Protocol Ports ------+-------------+-----------+----------------------------------------------- 1 Po1(SU) LACP Gi1/0/1(P) Gi1/0/2(P) ``` Both ports show `(P)` indicating they are bundled. `Po1(SU)` means the port-channel is in use. ### Show EtherChannel Port-Channel Detail ``` DIST-SW1# show etherchannel port-channel Channel-group listing: ------------------------ Channel-group 1 Protocol: LACP Partner: CORE-SW1 Aging-Time: 30 sec Max-ports: 8 Min-thresh: 0 Ports in the group: ------------------- Port: Gi1/0/1 ---------- Age of the port in the current state: 45 seconds Port: Gi1/0/2 ---------- Age of the port in the current state: 42 seconds Time since last bundle was loaded: 48 seconds Last bundle was loaded by: Gi1/0/1 Time since last unbundle occurred: Never Protocol Expiration Time: 30 seconds Ports requiring a module number update from negotiation: none ``` Both ports are active members. The "last bundle loaded" confirms LACP negotiation succeeded. ### Show LACP Neighbor ``` DIST-SW1# show lacp neighbor Flags: S - Device is requesting Slow LACPDUs F - Device is requesting Fast LACPDUs A - Device is in Active mode P - Device is in Passive mode Channel group 1 neighbors LACP neighbors: 1 Telnet Address IPv4: 10.0.0.1 Partner ID : 1111.1111.1111 Port Number : 1 Partner Port : 1 Port State : 32 Port Priority : 32768 Partner Port Priority: 32768 Aging Time : 30 Telnet Address IPv4: 10.0.0.1 Partner ID : 1111.1111.1111 Port Number : 2 Partner Port : 2 Port State : 32 Port Priority : 32768 Partner Port Priority: 32768 Aging Time : 30 ``` This confirms CORE-SW1 (partner ID 1111.1111.1111) is the other end of the bundle. Port numbers match correctly. ### Verify Trunk VLAN Carriage on Port-Channel ``` DIST-SW1# show interfaces Port-Channel 1 trunk Port Mode Encapsulation Status Native vlan Po1 on 802.1q trunking 99 Port Vlans allowed on trunk Po1 10,20,30,40,99,100 Port Vlans allowed and active in management domain Po1 10,20,30,40,99,100 Port Vlans in spanning tree forwarding state and not pruned Po1 10,20,30,40,99,100 ``` All VLANs are active and not pruned on the trunk. ### Show Interface Status on the Port-Channel ``` DIST-SW1# show interfaces Port-Channel 1 Port-channel 1 is up, line protocol is up (connected) Hardware is EtherChannel, address is 1111.1111.1111 (bia 1111.1111.1111) Description: Link to CORE-SW1 MTU 1500 bytes, BW 20000000 Kbit/sec Encapsulation ARPA, loopback not set Keepalive set (10 sec) Full-duplex, 10 Gb/s ``` Note the bandwidth is reported as 20 Gbps (10 Gbps × 2 links). The line protocol is "up." ## Troubleshooting EtherChannel Bundle Formation ### Symptom: Channel-Group Formed But Ports Show "p" (Suspended) Example: ``` Group Port-channel Protocol Ports ------+-------------+-----------+----------------------------------------------- 1 Po1(SD) LACP Gi1/0/1(p) Gi1/0/2(p) ``` **Causes**: Speed mismatch, duplex mismatch, or VLAN membership conflict. **Diagnosis**: ``` DIST-SW1# show interfaces GigabitEthernet1/0/1 | include speed|duplex MTU 1500 bytes, BW 10000000 Kbit/sec Full-duplex, 10 Gb/s DIST-SW1# show interfaces GigabitEthernet1/0/2 | include speed|duplex MTU 1500 bytes, BW 1000000 Kbit/sec Half-duplex, 100 Mb/s ``` Here, Gi1/0/2 negotiated 100 Mbps half-duplex. Fix: ``` DIST-SW1(config)# interface GigabitEthernet1/0/2 DIST-SW1(config-if)# no shutdown DIST-SW1(config-if)# speed 10000 DIST-SW1(config-if)# duplex full DIST-SW1(config-if)# end ``` ### Symptom: Ports Assigned to Channel-Group But Not Bundling ``` Group Port-channel Protocol Ports ------+-------------+-----------+----------------------------------------------- 1 Po1(SD) LACP Gi1/0/1(D) Gi1/0/2(D) ``` **Causes**: LACP negotiation failing, typically due to: - One side is `passive` and the other side is also `passive` (no LACP negotiation). - Cable disconnect or link down. - LACP timeout (check `show lacp neighbor` for "Aging Time"). **Diagnosis**: ``` DIST-SW1# show lacp neighbor ! If no neighbors appear, LACP PDUs are not reaching the far end. ! Check physical link: show interfaces GigabitEthernet1/0/1 ``` **Fix**: Ensure at least one side uses `mode active`: ``` DIST-SW1(config)# interface range GigabitEthernet1/0/1 - 2 DIST-SW1(config-if-range)# channel-group 1 mode active DIST-SW1(config-if-range)# end ``` ### Symptom: Port-Channel Created But Incomplete Traffic Flow **Cause**: Not all ports bundled into the channel-group. Only some ports carry traffic. **Diagnosis**: ``` DIST-SW1# show etherchannel summary ! Shows only Gi1/0/1(P) bundled, Gi1/0/2 missing or showing (D). ``` **Fix**: Ensure all intended ports are configured with the same channel-group number: ``` DIST-SW1(config)# interface range GigabitEthernet1/0/1 - 4 DIST-SW1(config-if-range)# channel-group 1 mode active ``` ### Symptom: LACP Timeout After Failover When one port fails, the other quickly takes over, but LACP reports aging issues. **Diagnosis**: ``` DIST-SW1# show lacp neighbor ! "Aging Time" decrements. If it reaches 0, the neighbor is aged out. ``` **Fix**: Ensure both ports are up on both switches. If a port goes down, manually shut it down and bring it back up: ``` DIST-SW1(config)# interface GigabitEthernet1/0/1 DIST-SW1(config-if)# shutdown DIST-SW1(config-if)# no shutdown ``` ## Comparison: LACP vs PAgP Standard LACP (802.3ad)IEEE 802.3ad PAgP (Cisco)Proprietary (Cisco) Interop LACP (802.3ad)Vendor-independent PAgP (Cisco)Cisco only Modes LACP (802.3ad)active, passive, on PAgP (Cisco)desirable, auto, on Performance LACP (802.3ad)Identical PAgP (Cisco)Identical Recommended LACP (802.3ad)**Yes** PAgP (Cisco) Legacy; avoid new configs LACP is the clear winner for any multi-vendor environment. Use PAgP only on old Catalyst 6500 or 4500 running ancient IOS. ## Load-Balancing Best Practices - **Data Center / Campus Core**: Use `src-dst-ip` to distribute traffic across flows. - **Access Layer**: `src-mac` is usually sufficient; most flows originate from different end-users. - **Monitor with `show etherchannel load-balance`**: ``` DIST-SW1# show etherchannel load-balance EtherChannel Load-Balancing Configuration: src-dst-ip EtherChannel Load-Balancing Addresses used for Forwarding: Reachable Tunnel Peer: 10.0.0.1 ``` ## Key Takeaways - **LACP dynamically bundles multiple links** without operator intervention if either side initiates negotiation. - **Use `active` mode on both sides** or `active` on one side and `passive` on the other; never `passive` on both. - **All bundled ports must have identical speed and duplex**; mismatches immediately suspend the port. - **Port-Channel interface is where you configure trunk mode and VLANs**; member ports inherit switchport behavior. - **Verify with `show etherchannel summary` and `show lacp neighbor`** to confirm bundle health and negotiation state.