Core
EtherChannel
EtherChannel bundles multiple physical links into one logical link to increase bandwidth and provide redundancy while avoiding STP blocking of individual members.
What you need to know
- Two negotiation protocols exist: PAgP (Cisco proprietary) and LACP (IEEE 802.3ad, open standard).
- PAgP modes: desirable (active) and auto (passive); desirable-desirable or desirable-auto form a channel, auto-auto does not.
- LACP modes: active and passive; active-active or active-passive form a channel, passive-passive does not.
- Mode on with on forms a channel unconditionally without any negotiation protocol.
- All bundled ports must match speed, duplex, trunk/access mode, and allowed VLANs before joining the channel.
- Up to 8 active links can be bundled in a single EtherChannel (with additional standby links using LACP).
- STP treats the entire EtherChannel as a single logical link, avoiding blocking of individual member ports.
Configuration commands
| Command | Mode | Purpose |
|---|---|---|
| interface range fastethernet 0/1 - 2 | config | Select the physical interfaces to bundle. |
| channel-group 1 mode active | config-if-range | Add interfaces to EtherChannel 1 using LACP active mode. |
| channel-group 1 mode passive | config-if-range | Add interfaces using LACP passive mode. |
| channel-group 1 mode desirable | config-if-range | Add interfaces using PAgP desirable mode. |
| channel-group 1 mode auto | config-if-range | Add interfaces using PAgP auto mode. |
| channel-group 1 mode on | config-if-range | Force the channel to form without negotiation. |
| interface port-channel 1 | config | Configure the logical port-channel interface. |
| switchport mode trunk | config-if | Configure the port-channel interface as a trunk (applies to all members). |
Verify it
- show etherchannel summary
- show etherchannel port-channel
- show interfaces port-channel 1
- show spanning-tree
- show run interface port-channel 1
Common mistakes
- Mixing incompatible modes such as PAgP auto with LACP passive, which never forms a channel.
- Configuring mismatched switchport settings (speed, duplex, VLANs) across member ports before bundling.
- Forgetting to apply trunk/access configuration on the port-channel interface itself.
- Using auto-auto (PAgP) or passive-passive (LACP), which fails to negotiate a channel.
- Changing member port configuration directly instead of through the port-channel interface, causing inconsistency errors.
Practise EtherChannel in a real CLI
Generated labs, graded against the simulated network state.