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CCNA FAQ: Frame Relay Configuration

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CCNA FAQ: Frame Relay Configuration

Q1. Imagine two Cisco routers, R1 and R2, using a Frame Relay service. R1 connects to a switch that uses LMI type ANSI T1.617, and R2 connects to a switch that uses ITU Q.933a. What keywords could be used in the R1 and R2 configuration so that the LMIs work correctly?
a. ansi and itu
b. T1617 and q933
c. ansi and q933
d. T1617 and itu
e. This won’t work with two different types.

Answer: C. The correct keywords are ansi and q933. However, the routers autodetect the LMI type by default, so not configuring the LMI also works.

Q2. BettyCo has five sites, with routers connected to the same Frame Relay network. VCs have been defined between each pair of routers. Betty, the company president, will fire anyone who configures anything that could just as easily be left as a default. Which of the following configuration commands, configured for the Frame Relay network, would get the engineer fired? (Choose three answers.)
a. ip address
b. encapsulation
c. lmi-type
d. frame-relay map
e. frame-relay inverse-arp

Answer: C, D, and E. The LMI type is autosensed by default. Inverse ARP is on by default as well, meaning that it does not need to be enabled with the frame-relay inverse-arp command, nor do any static mapping statements need to be added.

Q3. WilmaCo has some routers connected to a Frame Relay network. R1 is a router at a remote site, with a single VC back to WilmaCo’s headquarters. The R1 configuration currently looks like this:
interface serial 0/0
ip address 10.1.1.1 255.255.255.0
encapsulation frame-relay
Wilma, the company president, has heard that point-to-point subinterfaces are cool, and she wants you to change the configuration to use a point-to-point subinterface. Which of the following commands do you need to use to migrate the configuration? (Choose two answers.)
a. no ip address
b. interface-dlci
c. no encapsulation
d. encapsulation frame-relay
e. frame-relay interface-dlci

Answer: A and E. The IP address moves to the subinterface, so it needs to be removed from the serial interface first (with the no ip address command). The encapsulation stays on the physical interface. The frame-relay interface-dlci command must be used on the subinterface so that the router knows which DLCI goes with which subinterface—even if only one DLCI exists.

Q4. WilmaCo has another network, with a main site router that has ten VCs connecting to the ten remote sites. Wilma now thinks that multipoint subinterfaces are even cooler than point-to-point. The current main site router’s configuration looks like this:
interface serial 0/0
ip address 172.16.1.1 255.255.255.0
encapsulation frame-relay
Wilma wants you to change the configuration to use a multipoint subinterface. Which of the following do you need to use to migrate the configuration? (Note: DLCIs 101 through 110 are used for the ten VCs.)
a. interface-dlci 101 110
b. interface dlci 101-110
c. Ten different interface-dlci commands
d. frame-relay interface-dlci 101 110
e. frame-relay interface dlci 101-110
f. Ten different frame-relay interface-dlci commands

Answer: F. You can code only one DLCI on a frame-relay interface-dlci command, and you need one for each VC under the multipoint interface.

Q5. Which of the following commands lists the information learned by Inverse ARP?
a. show ip arp
b. show arp
c. show inverse arp
d. show frame-relay inverse-arp
e. show map
f. show frame-relay map

Answer: F

Q6. Which of the following are Frame Relay PVC status codes for which a router sends frames for the associated PVC? (Choose two answers.)
a. Up
b. Down
c. Active
d. Inactive
e. Static
f. Deleted

Answer: C and E. Up and down are not PVC status codes. Inactive means that the switch thinks a defined PVC is not working, and deleted means that the DLCI is not defined at the switch.

Q7. Central site router RC has a VC connecting to ten remote routers (R1 through R10), with RC’s local DLCIs being 101 through 110, respectively. RC has grouped DLCIs 107, 108, and 109 into a single multipoint subinterface S0/0.789, whose current status is “up and up.” Which of the following must be true? (Choose two answers.)
a. Serial 0/0 could be in an up/down state.
b. The PVC with DLCI 108 could be in an inactive state.
c. The show frame-relay map command lists mapping information for all three VCs.
d. At least one of the three PVCs is in an active or static state.

Answer: B and D. For a Frame Relay subinterface to be in an up/up state, the underlying physical interface must be in an up/up state, and at least one of the PVCs associated with the subinterface must be in one of the two working PVC states (active or static). The reason answer B can also be true is that if the PVC with DLCI 108 is inactive, the PVCs with DLCI 107 or 109 can be active, and the subinterface still be up/up.

Q8. Frame Relay router R1 uses interface S0/0 to connect to a Frame Relay access link. The physical interface is in an up/down state. Which of the following could cause this problem? (Choose two answers.)
a. The access link has a physical problem and cannot pass bits between the router and switch.
b. The switch and router are using different LMI types.
c. The router configuration is missing the encapsulation frame-relay command on interface S0/0.
d. The router received a valid LMI status message that listed some of the DLCIs as inactive.

Answer: B and C. For a Frame Relay physical interface to have a line status of “up,” the same physical layer features as used on leased lines must be working. To also have a protocol status of “down,” either the router is missing the encapsulation frame-relay command, or the router and switch disagree about the LMI type.

Q9. There are three virtual circuit design strategies for a Frame Relay cloud. Explain what these are and the advantages and disadvantages associated with each.

Answer: The three Frame Relay virtual circuit design strategies are hub and spoke, partial mesh, and full mesh. Hub and spoke is the cheapest design; however, it also offers the least amount of redundancy. If the hub location fails, the entire WAN mesh goes down. In addition, the hub and spoke design increases the amount of delay for packets traveling between the spoke locations. This can be devastating for VoIP traffic. Partial mesh designs connect key sites with multiple virtual circuits. This offers redundancy for those key locations, but can become a more costly design. Full mesh offers the ultimate level of redundancy and delay guarantees, but requires a huge monthly cost to support the large number of circuits.

Q10. Write a brief definition for the following terms:

  • Local Management Interface
  • Data Link Connection Identifier
  • Local Access Rate
  • Committed Information Rate
Answer: Local Management Interface (LMI): This is the language spoken between your Frame Relay router and the service provider that is used to provide DLCI status and traffic statistics.
Data Link Connection Identifier (DLCI): This is the Data Link address used to identify virtual circuits in the Frame Relay cloud.
Local Access Rate: This is the maximum physical speed your interface connected to the Frame Relay cloud can use.
Committed Information Rate: This is the level of bandwidth the service provider commits to give you on a regular basis.

Q11. When you connect a router to a Frame Relay network, the service provider transmits DLCI information to your router via LMI. How does the router then find the Layer 3 address to associate with the circuit?

Answer: After your router receives DLCI information, it sends Inverse ARP messages to each DLCI number requesting the Layer 3 address of the remote router.

Q12. When connecting a router to a Frame Relay network with multiple destinations, split-horizon issues can occur. Explain why this is and the two methods you could use to fix these issues.

Answer: Split-horizon is a loop-prevention mechanism that prevents a router from advertising a route out the same interface that received the original route advertisement. It can cause problems with Frame Relay because a hub router could have multiple destinations connected to a single physical interface. When those destinations send advertisements to the hub router, split horizon prevents the router from propagating the advertisements to other remote offices. The two methods you can use to resolve this issue are disabling the split-horizon mechanism or using point-to-point subinterfaces.

Q13. You are troubleshooting a Frame Relay network. It appears that your router is not receiving any DLCI information. What command(s) would you use to begin troubleshooting this problem and why?

Answer: The command you would be most likely to use to troubleshoot the failed DLCI communication is the show frame-relay lmi command. It enables you to focus on the communication with the Frame Relay service provider. If necessary, you may also use the debug frame-relay lmi command to probe deeper into the messages exchanged between your router and the service provider.

Q14. Into what categories of network does Frame Relay fit? (Choose 2.)
A. Circuit-switched
B. Packet-switched
C. Broadcast multi-access
D. NBMA

Answer: B, D. Frame Relay is considered a packet-switched network and operates in much the same way as X.25 and ATM. Rather than have users connected directly together over leased lines, virtual circuits are established through the service provider network. Frame Relay also falls under the NBMA category. This means that, by default, multiple devices can access the network, but broadcast messages are not forwarded. Answer A is incorrect because circuit-switched networks encompass connections that use the telephone company as a backbone. Answer C is incorrect because it describes ethernet connectivity, not Frame Relay.

Q15. Which of the following connections describe an on-demand circuit through the Frame Relay cloud that is created when needed and then destroyed after data has been transmitted?
A. PVC
B. SVC
C. DID
D. DOD

Answer: B, A. SVC is an on-demand circuit through the Frame Relay cloud that is created when needed and then destroyed after data has been transmitted. This circuit type is not commonly used and has been widely replaced by PVCs, which is Answer A. Answers C and D are incorrect because these acronyms have nothing to do with Frame Relay.

Q16. Which of the following are valid LMI signaling types? (Choose 3.)
A. Cisco
B. IETF
C. ANSI
D. Q.933a

Answer: A, C, D. The valid LMI signaling methods are Cisco, ANSI, and Q.933a. Answer B is incorrect because IETF represents the industry standard Frame Relay encapsulation that allows non-Cisco devices to interoperate with Cisco devices over a Frame Relay cloud.

Q17. According to Figure 23.12, what DLCI would be used if a client in Minnesota wanted to send information to a server in California?

A. 501
B. 502
C. 601
D. 602

Answer: A. DLCI addressing works exactly opposite of how most folks think it should work. Rather than send to a destination DLCI number, you leave on a local DLCI number. In this case, the Minnesota router would leave on DLCI 501 to reach the California office. Answer B is incorrect because California would leave on DLCI 502 to get to Arizona. Answers C and D are incorrect because they reference the connection between Minnesota and Texas.

Q18. A router connected to a Frame Relay service provider can occasionally send faster than the subscribed _________, but never faster than the _________.
A. Local Access Rate, CIR
B. Virtual Circuit Speed, CIR
C. CIR, Virtual Circuit Speed
D. CIR, Local Access Rate

Answer: D. A router connected to a Frame Relay service provider can often send faster than the Committed Information Rate (CIR), but never faster than the Local Access Rate. The CIR describes the minimum amount of bandwidth that the service provider contractually guarantees the client. The Local Access Rate references the fastest physical speed the line can handle. Answers B and C are incorrect because there is no such thing as a Virtual Circuit Speed. Answer A is incorrect because the terms are reversed.

Q19. If your router is sending too much information into the Frame Relay cloud, the service provider tags any return traffic with a ______ to notify your router to reduce its transmission rate.
A. D
B. BECN
C. FECN
D. Burst

Answer: B. The service provider tags any return traffic with a Backwards Explicit Congestion Notification (BECN) marking. By default, your router ignores these notifications. Answer A is incorrect because Discard Eligible (De) describes markings placed on any traffic sent above the CIR. Answer C is incorrect because Forward Explicit Congestion Notification (FECN) markings are placed on packets if there is no return traffic that can be marked with BECNs to tell the sender to slow down. Answer D is what happens to a balloon if you poke it with a needle.

Q20. By default, Cisco routers receive LMI messages from the service provider that provide all usable DLCI numbers for the local circuit. How does your router find out the remote devices it is able to reach?
A. The router sends Hello messages down each virtual circuit.
B. The router uses CDP to discover its directly connected neighbors.
C. The router uses Inverse ARP messages.
D. The router does not need to do anything; LMI signaling from the service provider autoconfigures the router.

Answer: C. After the routers receive the DLCI information through LMI signaling, they send Inverse ARP messages through to the other side of the connection. This enables them to discover the remote IP addresses they are able to reach. Answer A is incorrect because Hello messages are specific to routing protocols such as OSPF and EIGRP. Answer B is incorrect because Cisco Discovery Protocol enables you to see information just about directly connected Cisco devices. Answer D is incorrect because LMI can only give your routers the DLCI numbers it can use to reach remote devices, but cannot tell the router how the remote devices are configured.

Q21. You have two routers connected over a Frame Relay network. The router in Arizona has the IP address 10.1.1.1/24 and uses a local DLCI of 512. The router in Michigan has the IP address 10.1.1.2/24 and uses a local DLCI of 598. Which syntax among the following choices correctly creates a static map that enables Arizona to reach Michigan and allows routing protocol functionality?
A. frame-relay map ip 10.1.1.2 512 broadcast
B. frame-relay map ip 10.1.1.1 512 broadcast
C. frame-relay map ip 10.1.1.2 598 broadcast
D. frame-relay map ip 10.1.1.1 598 broadcast

Answer: A. The correct syntax of the Frame Relay map command is frame-relay map ip <remote_ip_address> <local_dlci> broadcast. The broadcast keyword enables routing protocol updates to function. In this case, Arizona is trying to reach the remote IP address in Michigan of 10.1.1.2, and uses the local DLCI of 512 to get there. All other answers use either the wrong DLCI or IP address.

Q22. You are configuring your router’s Serial 0 interface to communicate across the Frame Relay cloud with a non-Cisco router. You would like to use the Inverse ARP feature of the router to avoid configuring static maps; what command would you use to enable this feature?
A. encapsulation frame-relay
B. inverse-arp frame-relay
C. ietf inverse-arp
D. encapsulation frame-relay ietf

Answer: D. To use the industry standard Frame Relay encapsulation, you need to type in encapsulation frame-relay ietf. This enables Inverse ARP to map your Frame Relay circuits for you. Answer A is incorrect because this uses the Cisco proprietary Frame Relay encapsulation that does not work with any non-Cisco gear. The other two answers use invalid syntax and commands.

Q23. You are troubleshooting your Frame Relay connections. After typing in the show frame-relay pvc command, one of your PVCs shows up as DELETED. What causes this?
A. Your router is incorrectly configured. You need to add the right DLCI information and the circuit should come up.
B. The remote router is incorrectly configured.
C. You are physically disconnected from the service provider.
D. You need to switch from a multipoint configuration to a point-to-point configuration and create a subinterface for each PVC you plan on using.

Answer: A. Three primary PVC states indicate the status of the line. ACTIVE means there are no problems. INACTIVE means that there is a problem with the remote router, which rules out Answer B. DELETED means that there is a problem with your local router. Typically, this is caused by using the incorrect DLCI information. Answer D is eliminated because multipoint and point-to-point designs use DLCI information in the same way. If the DLCI shows up as DELETED under a multipoint configuration, it shows up as DELETED under a point-to-point configuration. Finally, if you were physically disconnected from the service provider, you would not see DLCI information (because LMI is used to send the DLCI status to your router), making answer C incorrect.

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