2 bandwidth limit for the same cable modem

[JAG]

My ISP is providing a high bandwidth for local intranet that is users of the same ISP can connect with a bandwidth of 2 Mbps where as downloading
from the internet has only 256 kbps. How this is implemented?
Even any Hint will be helpful
thnx in advance

[Keefe]

I would think that they have implemented a special rule on their router will allows higher transfer speeds on their "internal" network, while still giving you the slower transfer speeds to the open internet.