A network administrator is verifying a newly deployed link aggregation bundle between Switch-A and Switch-B. The command `show etherchannel summary` on Switch-A displays Port-channel 5 as `Po5(SD)` with member interfaces `GigabitEthernet1/0/1(I)` and `GigabitEthernet1/0/2(I)` running protocol `LACP`. On Switch-B, `show etherchannel summary` displays `Po5(SD)` with member interfaces `GigabitEthernet1/0/1(I)` and `GigabitEthernet1/0/2(I)` running protocol `PAgP`.
Which TWO statements accurately describe why Port-channel 5 fails to bundle and remains in a down state?
- Switch-A and Switch-B are running conflicting EtherChannel negotiation protocols, which prevents dynamic link aggregation setup.Cevap
- Switch-B physical interfaces were configured with `channel-group 5 mode auto` or `channel-group 5 mode desirable`, which explicitly selects PAgP instead of LACP.Cevap
- CBoth switches are operating in passive negotiation modes, which prevents either switch from sending protocol initiation frames.
- DA native VLAN mismatch exists on Port-channel 5, causing the switches to automatically force member interfaces into standalone `(I)` mode.
Cevap
The bundle fails because Switch-A and Switch-B are configured with mismatched EtherChannel protocols (LACP vs. PAgP), caused by Switch-B using `channel-group 5 mode auto` or `mode desirable`.
EtherChannel requires both endpoints to run the same aggregation protocol. Switch-A is configured for LACP (via `mode active` or `mode passive`), whereas Switch-B is configured for PAgP (via `mode auto` or `mode desirable`). Because LACP and PAgP control frames are incompatible, negotiation fails, leaving member interfaces in standalone state `(I)` and the port-channel down `(SD)`.
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Anahtar Kavram
Layer 2 EtherChannel LACP vs. PAgP Protocol Compatibility and CLI Mode Selection