A router designated to forward packets between autonomous systems (AS) is known as what?

The correct term for a router designated to forward packets between autonomous systems is commonly referred to as a "gateway router." This type of router is critical in managing the flow of data between different networks, particularly when those networks are under separate administrative domains—known as autonomous systems.

In a broader context, gateway routers facilitate BGP (Border Gateway Protocol) operations, which is the core protocol used for exchanging routing information between autonomous systems on the internet. This is essential for ensuring that data packets can be directed through the correct pathways, ultimately reaching their intended destination across various interconnected networks.

The other options do not accurately describe this specific function. For instance, "border system" is not a standard term used in networking, while "edge router" typically refers to a device located at the edge of a network that connects to external networks but does not specifically indicate that it handles traffic between different autonomous systems. "Core router" is associated with routing large amounts of data within a single autonomous system or a backbone network rather than between different systems. Thus, the designation of a router that forwards packets between autonomous systems is aptly captured by the term "gateway router."