Both Sides Set to LACP Passive — No Bundle Forming
Presenting Symptom
An EtherChannel between two switches does not form, and both sides show the port-channel interface in a down/down state.
Network Context
Two Cisco Catalyst 2960 switches (running IOS 15.0) are connected via four Gigabit Ethernet links in a small branch office. The interfaces are configured for LACP EtherChannel, but the port-channel remains down. The network engineer has verified physical connectivity and that all interfaces are up/up individually.
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 port-channel is up (SU) but all member ports are in stand-alone state (I). This indicates LACP negotiation is failing; the ports are not forming a 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 AdminFlags OperFlags Port Port
Port Flags Priority Dev ID Age key Key Number State
Gi0/1 SP 32768 0011.2233.4455 10s 0x0 0x0 0x0 0x0
Gi0/2 SP 32768 0011.2233.4455 10s 0x0 0x0 0x0 0x0
Gi0/3 SP 32768 0011.2233.4455 10s 0x0 0x0 0x0 0x0
Gi0/4 SP 32768 0011.2233.4455 10s 0x0 0x0 0x0 0x0The neighbor is sending Slow LACPDUs (S) and is in Passive mode (P). The Oper key and port state are 0x0, indicating no agreement. Both sides are passive, so neither initiates negotiation.
Check LACP internal state
show lacp internalFlags: 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
LACP port AdminFlags OperFlags Port Port
Port Flags State Priority Key Key Number State
Gi0/1 SP bndl 32768 0x1 0x1 0x101 0x3D
Gi0/2 SP bndl 32768 0x1 0x1 0x102 0x3D
Gi0/3 SP bndl 32768 0x1 0x1 0x103 0x3D
Gi0/4 SP bndl 32768 0x1 0x1 0x104 0x3DLocal ports are in Passive mode (P) and state is 'bndl' but that is misleading; the bundle state is local only. The key fact is both sides are passive, so no LACP negotiation occurs.
Verify interface configuration
show running-config interface gigabitEthernet 0/1interface GigabitEthernet0/1 channel-group 1 mode passive !
The interface is configured with 'channel-group 1 mode passive'. This confirms the root cause: both switches are set to LACP passive mode, so neither sends LACPDUs to initiate the bundle.
Root Cause
Both switches are configured with LACP mode 'passive'. In LACP, at least one side must be in 'active' mode to initiate negotiation. When both are passive, no LACPDUs are exchanged, and the EtherChannel does not form.
Resolution
Verification
After applying the fix, verify the EtherChannel forms: show etherchannel summary Expected output: 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, 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(P) Gi0/2(P) Gi0/3(P) Gi0/4(P) The ports now show (P) indicating they are bundled in the port-channel.
Prevention
1. Always ensure at least one side of an LACP EtherChannel is configured as 'active'. 2. Use a consistent configuration template for EtherChannel to avoid mismatched modes. 3. Verify LACP mode during initial setup and after any configuration changes.
CCNA Exam Relevance
On the CCNA 200-301 exam, this scenario tests knowledge of LACP modes (active/passive) and the requirement that at least one side must be active. Questions may present a troubleshooting scenario where an EtherChannel fails to form, and the candidate must identify that both sides are passive. The exam expects candidates to know that 'passive' only responds to LACPDUs, while 'active' initiates negotiation.
Exam Tips
Remember: LACP passive = waits for partner; LACP active = initiates. Both passive = no negotiation.
The 'show etherchannel summary' command is key to quickly identifying stand-alone ports (I flag).
In the exam, be careful not to confuse LACP passive with PAgP desirable/auto; PAgP uses different terminology.
Commands Used in This Scenario
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