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Network Warrior, 2nd Edition by Gary A. Donahue

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Cross-Stack EtherChannel

Sometimes you can create an EtherChannel across two physical switches. For example, when 3750s are stacked, the stack becomes a single logical entity and each physical switch acts like a blade. Configuring an EtherChannel across two physical switches in the stack is possible, and even recommended to eliminate single physical failure points. Nothing special is required to accomplish this once the stack has been configured—just configure each port to be in the same port-channel group:

3750-IOS(config)#int range g1/0/1 , g2/0/1
3750-IOS(config-if-range)#channel-group 10 mode on
Creating a port-channel interface Port-channel 10

Cisco calls this cross-stack EtherChannel, and it has some interesting capabilities and limitations. For example, you can have 16 ports in a cross-stack EtherChannel, with 8 active and 8 in standby. You cannot use PAgP, though, so your modes are confined to active, passive, and on.

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