Is it true that MAC addresses are the only kind of addresses that a router will route? Please define the gadget you're referring to for those who responded yes, and could you do the same for those who said no?

While developing a reliable transport protocol, early versions of the protocol discussed in class used a NAK message, sent by the receiver to the sender to indicate a packet was not correctly received. This kind of message, however, is not found in further protocols, like GBN, SR or even TCP. Why not? In other words, why don't these protocols provide a way to signal to the sender that the received message was received with an error

Is there a significant difference between a modem and a router?

Why do you need to have a private network address? Is it feasible that a datagram with an address from a private network may at some time in the future become available on the whole public Internet? Explain.