EtherChannel Not Bundling — Ports Stay Individual
Presenting Symptom
Ports configured in an EtherChannel remain individual (not bundled) and the port-channel interface is down/down.
Network Context
A small branch office with two Cisco Catalyst 2960 switches connected via four trunk links. The switches run IOS 15.0(2) and are configured to form a single Layer 2 EtherChannel. The network engineer observes that the four physical ports are all up/up but the port-channel interface is down/down, and no traffic is passing over the bundle.
Diagnostic Steps
Check EtherChannel summary
show etherchannel summaryFlags: 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, no aggregation due to minimum links not met
m - not in use, port not aggregated due to 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(I) Gi0/2(I) Gi0/3(I) Gi0/4(I)The output shows that all four ports are in 'I' (stand-alone) state, meaning they are not bundled into the port-channel. The port-channel interface is up (SU) but no ports are bundled. This indicates a configuration mismatch or protocol issue.
Check EtherChannel port-channel detail
show etherchannel port-channelChannel-group listing: ---------------------- Group: 1 ---------- Port-channel: Po1 (Primary Aggregator) Age of the Port-channel = 0d:00h:05m:34s Logical slot/port = 2/1 Number of ports = 0 HotStandBy port = null Port state = Port-channel Ag-Inuse Protocol = LACP Port Security = Disabled Ports in the Port-channel: Index Load Port EC state No of bits ------+------+---------+------------------+----------- 0 00 Gi0/1 down 0 0 00 Gi0/2 down 0 0 00 Gi0/3 down 0 0 00 Gi0/4 down 0 Time since last port bundled: 0d:00h:00m:00s Gi0/1
The port-channel shows that all ports are in 'down' EC state, confirming they are not bundled. The 'Number of ports = 0' indicates no ports are active in the bundle.
Check LACP neighbor status
show lacp neighborFlags: S - Device is sending Slow LACPDUs F - Device is sending Fast LACPDUs
A - Device is in Active mode P - Device is in Passive mode
Channel group 1 neighbors
Partner's information:
LACP port Admin Oper Port Port
Port Flags Priority Dev ID Age key Key Number State
Gi0/1 SP 32768 0011.2233.4455 10s 800 0 0x1 0x7D
Gi0/2 SP 32768 0011.2233.4455 10s 800 0 0x2 0x7D
Gi0/3 SP 32768 0011.2233.4455 10s 800 0 0x3 0x7D
Gi0/4 SP 32768 0011.2233.4455 10s 800 0 0x4 0x7DThe output shows that LACP packets are being received from the neighbor (partner) with oper key 0. An oper key of 0 indicates that the neighbor's ports are not configured for LACP or are in a different channel group. This suggests a configuration mismatch on the neighbor switch.
Verify interface configurations on both switches
show running-config interface GigabitEthernet0/1Building configuration... Current configuration : 150 bytes ! interface GigabitEthernet0/1 switchport mode trunk channel-group 1 mode active !
Check that the channel-group number and mode match on both sides. Common mismatches: one side uses 'mode active' and the other uses 'mode passive' (LACP), or one side uses PAgP while the other uses LACP. Also verify that the channel-group number is the same on both switches.
Root Cause
The neighbor switch has the ports configured with 'channel-group 1 mode passive' while the local switch uses 'channel-group 1 mode active'. LACP requires at least one side to be active; if both are passive, LACP negotiation fails. Additionally, the neighbor switch may have a different channel-group number (e.g., channel-group 2) causing the oper key to be 0.
Resolution
Verification
After applying the fix, run: ``` show etherchannel summary ``` Expected output: ``` Group Port-channel Protocol Ports ------+-------------+-----------+---------------------------------------------- 1 Po1(SU) LACP Gi0/1(P) Gi0/2(P) Gi0/3(P) Gi0/4(P) ``` All ports should show 'P' (bundled). Also verify the port-channel is up: ``` show interfaces port-channel 1 ``` Expected: 'Port-channel1 is up, line protocol is up'
Prevention
["Always configure the same EtherChannel protocol (LACP or PAgP) and mode on both ends.","Use consistent channel-group numbers on both switches.","Verify physical port parameters (speed, duplex, VLAN, trunking) match on all member ports."]
CCNA Exam Relevance
On the CCNA 200-301 exam, EtherChannel troubleshooting appears in multiple-choice questions and simulation labs. The exam tests understanding of LACP and PAgP modes, the requirement for consistent configuration on both ends, and the use of 'show etherchannel summary' to diagnose bundling issues. A key fact is that LACP requires at least one side to be active; if both are passive, the channel will not form.
Exam Tips
Memorize the LACP modes: active (sends LACPDUs) and passive (responds only). At least one side must be active.
Know that 'show etherchannel summary' flags: P = bundled, I = stand-alone, s = suspended.
Remember that mismatched channel-group numbers cause oper key of 0 in 'show lacp neighbor'.
Commands Used in This Scenario
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