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EtherChannelCCNA 200-301

Only Some Ports Bundling in EtherChannel — Not All Members Active

Presenting Symptom

An EtherChannel is configured between two switches, but only some member ports are bundled; the remaining ports remain in standalone mode, causing inconsistent load balancing and potential loops.

Network Context

Two Cisco Catalyst 2960 switches (IOS 15.0) are connected via four Gigabit Ethernet ports configured as a single LACP EtherChannel. The network is a small branch office with a single VLAN. The EtherChannel is intended to provide increased bandwidth and redundancy between the access and distribution layers.

Diagnostic Steps

1

Check EtherChannel summary

show etherchannel summary
Flags:  D - down        P - bundled in port-channel
        I - stand-alone s - suspended
        H - Hot-standby (LACP only)
        R - Layer3      S - Layer2
        U - in use      N - not in use, no aggregation
        f - failed to allocate aggregator

        M - not in use, minimum links not met
        u - unsuitable for bundling
        w - waiting to be aggregated
        d - default port


Number of channel-groups in use: 1
Number of aggregators:           1

Group  Port-channel  Protocol    Ports
------+-------------+-----------+----------------------------------------------
1      Po1(SU)         LACP      Gi0/1(P)    Gi0/2(P)    Gi0/3(I)    Gi0/4(I)

The output shows that only Gi0/1 and Gi0/2 are bundled (P), while Gi0/3 and Gi0/4 are in stand-alone (I) state. This indicates that not all ports are successfully negotiating LACP.

2

Check LACP neighbor details on one of the non-bundled ports

show lacp neighbor interface gigabitEthernet 0/3
Flags:  S - Device is sending Slow LACPDUs   F - Device is sending Fast LACPDUs
        A - Device is in Active mode       P - Device is in Passive mode


Partner information:

                  LACP port                        Admin    Oper    Port    Port
Port      Flags   State  Priority      Dev ID          Age key   Key   Number  State
Gi0/3     FA      ACTIVE 32768         0x0000.0000.0000  0s   0x0    0x0    0x0     0x0

The partner device ID is all zeros, meaning the neighbor is not sending LACP frames. This suggests a misconfiguration on the neighbor switch or a physical issue.

3

Check LACP configuration on the local switch for the non-bundled ports

show running-config interface gigabitEthernet 0/3
interface GigabitEthernet0/3
 switchport mode trunk
 channel-group 1 mode passive

The port is configured with channel-group 1 mode passive. For LACP to form, at least one side must be active. If the neighbor is also passive, the channel will not form.

4

Check LACP configuration on the neighbor switch for the corresponding ports

show running-config interface gigabitEthernet 0/3
interface GigabitEthernet0/3
 switchport mode trunk
 channel-group 1 mode passive

Both sides are configured as passive. LACP requires at least one side to be active to initiate negotiation. This is the root cause.

Root Cause

The LACP EtherChannel is only partially bundled because some member ports are configured with channel-group mode passive on both ends. LACP requires at least one side to be active to initiate negotiation; when both sides are passive, no LACP frames are exchanged, and the ports remain in stand-alone state.

Resolution

Change the LACP mode on one side to active for the affected ports. For example, on the local switch: interface range gigabitEthernet 0/3-4 channel-group 1 mode active This will cause the local switch to actively send LACP frames, allowing negotiation to complete. Alternatively, change both sides to active for consistency.

Verification

Run 'show etherchannel summary' again. Expected output: Group Port-channel Protocol Ports ------+-------------+-----------+---------------------------------------------- 1 Po1(SU) LACP Gi0/1(P) Gi0/2(P) Gi0/3(P) Gi0/4(P) All four ports should now show (P) bundled.

Prevention

1. Use a consistent LACP mode across all member ports: configure all ports as active to ensure negotiation always initiates. 2. Avoid mixing LACP modes on the same EtherChannel; if using passive, ensure the neighbor is active. 3. Verify LACP configuration during initial setup with 'show etherchannel summary' and 'show lacp neighbor'.

CCNA Exam Relevance

On the CCNA 200-301 exam, this scenario may appear as a troubleshooting question where you must identify why an EtherChannel is not fully operational. The exam tests understanding of LACP modes (active/passive) and the requirement that at least one side must be active. Candidates must know the 'show etherchannel summary' command and interpret the flags (P, I, S).

Exam Tips

1.

Memorize the LACP mode requirements: active-active or active-passive works; passive-passive does not.

2.

In 'show etherchannel summary', a port with flag 'I' means stand-alone (not bundled) — often due to LACP mode mismatch.

3.

Always check both sides of the link when troubleshooting EtherChannel issues.

Commands Used in This Scenario

show etherchannel summary

Displays the status and configuration of all EtherChannel interfaces on the switch, used to verify channel bundling, port membership, and protocol state.

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