3.4.2. Requirements and Verification

Verification:

Switch# 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

Number of channel-groups in use: 1

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

Switch# show etherchannel port-channel

Read a port-channel's flags together, one letter for the layer and one for the status: Po1(SU) is a Layer 2 channel in use, and (RU) would be a Layer 3 channel in use.

EtherChannel Requirements:

• Same speed and duplex on all ports
• Same VLAN configuration (access or trunk)
• Same allowed VLANs on trunks
• Same native VLAN on trunks

Note that STP port cost is not a bundling requirement. Once the members bundle, STP runs on the logical port-channel rather than on the physical interfaces, so a mismatched member cost does not keep a port out of the channel.

⚠️ Exam Trap: If EtherChannel members have mismatched configurations, they won't bundle. Use show etherchannel summary to check for ports in suspended (s) or stand-alone (I) state.