Chapter 8's Review Questions

1: Can a single Frame Relay PVC be assigned different DLCIs on each end of a virtual circuit?
A1: Answer: Yes. The term to know is “locally significant,” which means that a particular DLCI is significant only on the link between two frame devices. Think of DLCIs as the speed-dial numbers stored in your cell phone.
2: What are the three possible states for a Frame Relay PVC? Explain.
A2: Answer: Refer to Table 8-2 and Trouble Ticket 4. The three possible states for a PVC are active, inactive, and deleted.
3: What is the result if one end of the PVC is set to the default Cisco LMI type and the other end is set to ANSI or Q933A?
A3: Answer: As long as the Frame Relay switch attached to the local router is configured for the same LMI, the PVC works just fine. Remember that LMI is the signaling between the router and local frame switch, not an end-to-end function.
4: Can you ping yourself in Frame Relay? Why or why not?
A4: Answer: On point-to-point interfaces, yes. On multipoint interfaces, however, Frame Relay is NBMA, and in a hub-and-spoke topology there is no mapping for yourself. Certainly you could put in a map statement for yourself if you really wanted to make this happen.
5: Headquarters is connected to several branch office routers through a Frame Relay cloud. You know for a fact that the hub router is version 12.1, but you are not sure about all the remotes. Keepalive activity is occurring at most of the remote offices but not all of them. What should you check?
A5: Answer: Work through the layers. The physical connection is fine, but you are not receiving any kind of signal from a couple of pretty old existing sites. Perhaps the remote routers are something less than IOS 11.2 and need LMI configured on them. The command is frame-relay lmi-type [cisco | ansi | q933].
6: Headquarters is connected to several branch office routers through a Frame Relay cloud. The engineer at one of the branch offices is having problems communicating with another branch office. How can you help him out?
A6: Answer: Determine how the branch office is communicating. Determine whether the engineer can ping the other branch offices. Take a methodical approach and work through the layers, addressing the following points:

  • Find out whether the interfaces are up.

  • Check ports and cables.

  • Are you getting LMI?

  • Is there an encapsulation mismatch?

  • Are the DLCIs active and assigned properly?

  • Is there a static or dynamic mapping problem?

  • Did you forget the broadcast keyword for the routing updates?

  • Do you have a route?

  • Do you have split-horizon issues?

  • Are there any ACLs?

7: Explain the output of show frame-relay map in the following example:
r1#show frame-relay map
Serial1 (up): ip 192.168.5.6 dlci 104(0x68,0x1880), dynamic,
              broadcast,, status defined, active

A7: Answer: The show frame-relay map example indicates that s1 is up. DLCI 104 (68 in hex) maps to 192.168.5.6 using Inverse ARP. It displays dynamic, broadcast by the default nature of Inverse ARP and the PVC is active.
8: You have decided to contact your service provider about getting a higher CIR to allocate more bandwidth because you have been experiencing consistent problems with dropped packets due to congestion on the PVC. What command did you use to determine this?
A8: Answer: The show frame-relay pvc command is helpful in checking dropped packets and FECNs and BECNs. The presence of FECNs and BECNs does not necessarily indicate that frames were dropped by the service provider. That depends on how they police. If the service provider is generous and only marks excess frames as DE, you may make out fine.
9: In an all-Cisco-shop Frame Relay, Cisco encapsulation is fine. What Frame Relay encapsulation type is available for other vendors?
A9: Answer: The Frame Relay encapsulation types are the default Cisco and IETF for other vendors.
10: Point-to-point subinterfaces are often used in configuring Frame Relay to avoid the routing issues with main interfaces and multipoint configurations. Do you need an IP address on the main interface if using point-to-point subinterfaces?
A10: Answer: You should not configure an IP address on the main interface when configuring Frame Relay point-to-point subinterfaces. If one is configured, you can use no ip address to remove it and configure each subinterface with an address from a different subnet.
11: How does a router get a DLCI?
A11: Answer: Data-link connection identifiers (DLCIs) can be learned via Inverse ARP or manually configured. If manually assigned, you get the DLCI assignments from the service provider.
12: You are attempting to fix a bad IP address on a Frame Relay interface, but the mapping is still showing the old address. What should you do?
A12: Answer: The clear frame-relay-inarp command clears the dynamic Inverse ARP table.
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