350-401 · Question #251
One switch has EtherChannel configured as auto. What options on the other switch can be configured to establish an EtherChannel bundle?
The correct answer is C. Desirable. When one switch port is configured for EtherChannel as auto (PAGP passive), the other switch port must be configured as desirable (PAGP active) to actively negotiate and form an EtherChannel bundle.
Question
One switch has EtherChannel configured as auto. What options on the other switch can be configured to establish an EtherChannel bundle?
Options
- AAuto
- BActive
- CDesirable
- DPassive
How the community answered
(51 responses)- A16% (8)
- B4% (2)
- C75% (38)
- D6% (3)
Why each option
When one switch port is configured for EtherChannel as `auto` (PAGP passive), the other switch port must be configured as `desirable` (PAGP active) to actively negotiate and form an EtherChannel bundle.
If both switches are configured with `auto` mode (PAGP passive), neither will initiate EtherChannel negotiation, so a bundle will not form.
`Active` mode is part of LACP (Link Aggregation Control Protocol), not PAGP (Port Aggregation Protocol), which is implied by the `auto` mode.
The `desirable` mode for PAGP actively attempts to form an EtherChannel, initiating negotiation. When paired with `auto` mode (which is PAGP passive and only responds to negotiation requests), `desirable` will trigger the negotiation, allowing the EtherChannel to form.
`Passive` mode is also part of LACP, not PAGP, and would not actively initiate negotiation if the other side is `auto`.
Concept tested: EtherChannel negotiation modes (PAGP)
Source: https://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst3850/software/release/3se/lan_feature_config/guide/b_lan_3se_3850_feature_config_guide/b_lan_3se_3850_feature_config_guide_chapter_0100.html#ID360
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