1. What is used to identify the path to the next frame-relay switch in a Frame Relay network?
- CIR
- DLCI
- FECN
- BECN
Explanation: VCs are identified by DLCIs. DLCI values typically are assigned by the Frame Relay service provider (for example, the telephone company).
2. Why are Frame Relay paths referred to as virtual?
- There are no dedicated circuits to and from the Frame Relay carrier.
- Frame Relay PVCs are created and discarded on demand.
- The connections between PVC endpoints act like dialup circuits.
- There are no dedicated circuits inside the Frame Relay carrier cloud.
Explanation: Unlike leased lines, there are no dedicated circuits in the carrier’s Frame Relay network for end-to-end customer connectivity. Most providers use PVCs (some use SVCs) to create and discard circuits as customers purchase them without needing to deploy additional cabling.
3. Which statement accurately describes the split horizon problem with regard to a multipoint topology?
- Split horizon must be disabled for all non-IP protocols.
- Split horizon creates IP routing loops in multipoint domains.
- Split horizon does not apply to broadcasts, so it does not protect protocols that use broadcast updates.
- Split horizon prevents any point from accepting a valid update and forwarding to all the other points.
Explanation: Whether using a single physical interface, or an interface configured as a multipoint subinterface, when the remote ends of the virtual circuits are on the same subnet, it is subject to split horizon. If point-to-point subinterfaces are used with each virtual circuit on a separate subnet, split horizon is no longer an issue.
4. What are two reasons Frame Relay is more cost-effective than leased lines? (Choose two.)
- time division multiplexing
- uses less equipment
- optimized packet routing
- shares bandwidth across a large customer base
- dynamic IP addressing
Explanation: Frame Relay requires a single access line or circuit to the provider’s frame network cloud, regardless of the number of remote networks. A router with a single WAN interface and CSU/DSU is needed, along with a single access circuit. Frame Relay allows a provider to efficiently share the bandwidth within its cloud instead of deploying a large number of individual dedicated point-to-point links.
5. Match the status of a DLCI from the show frame-relay pvc command with its meaning.
6. What reliability advantage does Frame Relay offer over leased lines?
- Frame Relay access circuits are higher grade circuits than leased lines.
- The pathways for virtual circuits inside the carrier are meshed.
- From end to end, a single virtual circuit uses a fixed error-checked path.
- Frame Relay uses more sophisticated error detection methods.
Explanation: A Frame Relay cloud typically is a meshed network of circuits and Layer 2 switches (usually ATM). This allows for redundancy within the provider’s network that does not exist with a dedicated leased line.
7. Refer to the exhibit. What is placed in the address field of a frame that will travel from the Orlando office to the DC office?
- MAC address of the Orlando router
- MAC address of the DC router
- 192.168.1.25
- 192.168.1.26
- DLCI 100
- DLCI 200
Explanation: The Layer 2 encapsulation is Frame Relay, with the local DLCI used as the address.
8. Which situation favors a multipoint topology over point-to-point?
- when VLSM cannot be used to conserve addresses
- when using routing protocols other than IP
- when using a frame mesh topology to save access circuits
- when using a routing protocol that requires broadcast updates
Explanation: Point-to-point topologies typically requires a separate subnet for each point-to-point connection. In many networks VLSM is used to subnet one of the subnets as /30 networks. If this is not an option, multipoint topology can be used. Multipoint topology means that all the VCs share the same subnet address. (Note: In today’s modern networks, VLSM usually is an option.)
9. What is an advantage of configuring subinterfaces in a Frame Relay environment?
- makes the DLCIs globally significant
- eliminates the need for using Inverse ARP
- reduces split horizon issues
- improves flow control and bandwidth usage
Explanation: When point-to-point subinterfaces are used, each VC is on a separate subnet; therefore, split horizon is not an issue. From the perspective of the router, each VC is on a separate (logical) interface. This eliminates split horizon as an issue.
10. Which protocol can provide error correction for data that is transmitted over a Frame Relay link?
- FECN
- FTP
- LMI
- TCP
- UDP
Explanation: Frame Relay does not provide any error correction. Only the upper-layer protocol TCP, used by the host, provides any error detection when Frame Relay is used as the Layer 2 transport.
11. Drag the commands on the left to the description on the right.
12. At which rate does a service provider guarantee to transfer data into the Frame Relay network?
- baud rate
- timing rate
- data transfer rate
- committed information rate
Explanation: The CIR is the amount of data that the network receives from the access circuit. The service provider guarantees that the customer can send data at the CIR. All frames received at or below the CIR are accepted.
13. How are DLCI numbers assigned?
- They are assigned by a DLCI server.
- They are assigned arbitrarily by the user.
- They are assigned by the service provider.
- They are assigned based on the host IP address.
Explanation: The DLCI numbers are assigned by the service provider. Most providers allow the customer to choose its own DLCI numbers as long as they are valid numbers.
14. A router can reach multiple networks through a Frame Relay interface. How does the router know which DLCI to assign to the IP address of the destination network?
- It consults the Frame Relay map.
- It consults the routing table to find the DLCI.
- It uses Frame Relay switching tables to map DLCIs to IP addresses.
- It uses RARP to find the IP address of the corresponding DLCI.
Explanation: Frame Relay maps are used to map the remote network address to the local DLCI.
15. Drag the term on the left to the associated definition on the right.
