Two Cisco switches, SW-A and SW-B, need to form an EtherChannel. SW-A is configured with `channel-group 1 mode active`. To ensure the EtherChannel forms successfully, what specific mode must SW-B's corresponding interface be configured for?

To ensure the EtherChannel forms successfully, SW-B's corresponding interface must be configured for `channel-group 1 mode active` or `channel-group 1 mode passive`. This is because SW-A is configured with `mode active`, which implies the use of Link Aggregation Control Protocol (LACP), an open standard for EtherChannel negotiation.

EtherChannel is a port-channeling technology that aggregates multiple physical Ethernet links into a single logical link. This aggregation provides increased bandwidth capacity and link redundancy, ensuring network uptime even if individual physical links fail. Traffic is load-balanced across the active links within the channel.

The command `channel-group 1` assigns the interface to EtherChannel group number 1. The group number must be consistent across all interfaces intended to be part of the same logical EtherChannel on both switches.

When SW-A is configured with `mode active`, it means SW-A is actively participating in LACP negotiation. LACP is defined by IEEE 802.3ad and enables switches to automatically detect, negotiate, and maintain EtherChannel links. A switch configured in `active` mode actively sends LACP packets to its peer, attempting to initiate and establish an EtherChannel.

For SW-B to successfully form an EtherChannel with SW-A, it must also utilize LACP in a compatible mode:

If SW-B is configured with `mode active`, it will also actively send LACP packets, similar to SW-A. When both switches are in `active` mode, they both initiate the negotiation process, and an LACP-based EtherChannel will form successfully.

If SW-B is configured with `mode passive`, it will listen for incoming LACP packets from its peer but will not initiate LACP negotiation itself. Since SW-A is in `active` mode and is actively sending LACP packets, SW-B in `passive` mode will receive these packets, respond to the negotiation requests, and successfully form the LACP-based EtherChannel.

Therefore, SW-B needs to be either `active` (both initiating) or `passive` (SW-A initiates, SW-B responds) to establish the LACP EtherChannel with SW-A.