Cisco Certified Network Associate (CCNA) Practice Exam

How should a router that is being used in a Frame Relay network be configured to avoid split horizon issues?

1. Configure a separate sub-interface for each PVC with a unique DLCI and subnet assigned to the sub-interface.

2. Configure each Frame Relay circuit as a point-to-point line to support multicast and broadcast traffic.

3. Configure many sub-interfaces on the same subnet.

4. Configure a single sub-interface to establish multiple PVC connections to multiple remote router interfaces.

The correct answer is: Configure a separate sub-interface for each PVC with a unique DLCI and subnet assigned to the sub-interface.

Configuring a separate sub-interface for each Permanent Virtual Circuit (PVC) with a unique Data Link Connection Identifier (DLCI) and subnet assignment is essential in a Frame Relay network to avoid split horizon issues. Frame Relay inherently uses split horizon rules to prevent routing loops, meaning that multicast and broadcast traffic are not sent back out the same interface from which they were received. By assigning each PVC its own sub-interface along with a unique DLCI and separate subnet, it essentially creates a distinct logical interface for each circuit. This setup allows the router to treat each link as a separate connection to multiple remote networks. With this configuration, routers can send and receive broadcasts and multicasts properly because each sub-interface operates independently, effectively bypassing the split horizon rule that governs a single interface. This method ensures that routing information can be shared without running into the limitations imposed by split horizon, enabling more reliable network communication and efficient routing across the Frame Relay connections.