[mod50ack]

The difference is legal, not technical. You don't have the right to redistribute copyrighted material with permission, except according to exceptions to copyright law (which are narrow enough to not apply here). Cisco gives permission for users to use the software only if downloaded directly from Cisco, and doesn't grant anybody permission to mirror and redistribute it.

Can you tell if a copy was downloaded from Cisco directly? No. Does it make a technical difference? No. But those are the rules Cisco chose, and so there it is.

One potential reason I can think of for this happening is Cisco being required to count the number of downloads of the software (or something like that). But, in the end, there's no requirement that there be logical sense to a rule like this.

[userbinator]

Can you tell if a copy was downloaded from Cisco directly? No. Does it make a technical difference? No. But those are the rules Cisco chose, and so there it is.

Is it enforceable if there is no observable difference?

[mod50ack]

Legally, it is enforceable. That's not the same as practically enforceable.