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I manage a C3560 and have set the sdm-prefer like you said. Enter the command at the # prompt. Do not go to config t. My switch runs at layer 2 but has an IPv6 management address. Not sue if you must do this.
That's bizarre. Are you sure your IP isn't in that range? What's you subnet mask?If you're correct, this looks like a massive fail by your ISP. I don't even know how they would be sending you those packets. It would be interesting to do a wiresha...
