sorry new to brocade switching but:
When in layer2 mode with the icx6610 is the only mtu option either jumbo or no jumbo? I can't see where you can edit the size of the mtu outisde of the jumbo key word for an Ethernet packet.
You are correct, on Layer 2 code you can only enabled Jumbo Frames at the global level.
In L3 you can enbale on ports and VLAN level.
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