Chapter 4 – Frame Relay
Study Guide
After completion of this chapter, you should be able to:
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1.
Describe the fundamental concepts of Frame Relay technology, including operation, implementation
requirements, maps, and Local Management Interface (LMI) operation.
Configure a basic Frame Relay permanent virtual circuit (PVC), including configuring and troubleshooting Frame
Relay on a router serial interface and configuring a static Frame Relay map.
Describe advanced concepts of Frame Relay technology, including subinterfaces, bandwidth, and flow control.
Configure an advanced Frame Relay PVC, including solving reachability issues, configuring subinterfaces, and
verifying and troubleshooting a Frame Relay configuration.
At what layers of the OSI model does Frame Relay operate? Physical and Data Link
2. How is a Frame Relay connection different from that of a Leased Line?
Frame relay requires only a single access circuit to the Frame relay provider to communicate with multiple
other sites.
3. Why is Frame Relay more cost effective than Leased Lines?
Frame relay customers only pay for the local loop and for the BW they purchase from the network provider.
4. Complete Activity 4.1.1.5 – Identify Frame Relay Terminology and Concepts
5. Define the two types of Virtual Circuits (VC):
a. SVC – established dynamically by sending signaling messages to the network
b. PVC – preconfigured by the carrier, and after they are set up, only operate in Data Transfer and Idle
modes.
6. How is a VC identified? Using DLCI numbers
7. What does it mean that a DLCI is locally significant?
They are unique only to the physical channel on which they reside. Therefore, devices at opposite ends of a
connection can use the same DLCI values to refer to different virtual circuits.
8. How is a Star topology and Full Mesh topology different?
A star topology is created using links back to one central location while a full mesh topology links every
device to every other device. Full Mesh is the most expensive but most reliable topology.
9. What must be done before a Cisco router is able to transmit data over Frame Relay?
It needs to know which local DLCI maps to the Layer 3 address of the remote destination
10. Explain the following types of Frame Relay mapping:
a. Inverse ARP – router knows the DLCI and sends a request for the destination IP address
b. Dynamic Mapping – uses Inverse ARP to populate an address-to-DLCI mapping table on the FR
router.
c. Static Frame Relay Mapping – configuring a manual map for the next-hop IP address to a local DLCI.
11. What is the function of the Local Management Interface (LMI)?
A keepalive mechanism that provides status information about FR connections between the router (DTE)
and FR switch (DCE).
12. What optional information can be included in an LMI?
a. VC Status messages
b. Multicasting
c. Global Addressing
d. Simple flow control
13. What are the three LMI types supported by Cisco routers, and what command is used to configure the LIM
type?
Cisco, ANSI, and Q933A
R1(config-if)# frame-relay lmi-type [cisco | ansi | q933a]
14. Complete Activity 4.1.2.10 – Map the VC to the Port Number
15. Complete Activity 4.1.2.11 – Match Frame Relay Fields to the Definition
16. Complete Activity 4.1.2.12 – Identify LMI Terminology and Concepts
17. What is the function of the default LMI autosense feature?
Based on the LMI status messages it receives from the FR switch, the router automatically configures its
interface with the supported LMI type acknowledged by the frame relay switch. If the LMI type is manually
set, it disables the autosense feature.
18. What is the function of the CIR and how does it affect the cost of the link?
The CIR specifies the maximum average data rate provided to the customer. If customer sends info higher
than the CIR, it is not guaranteed and is marked with the DE bit. The lower the CIR, the lower the cost.
19. What is the difference between the Committed Burst Size (Bc) and Excess Burst Size (Be)?
Bc allows traffic to burst to higher speeds, as available network bandwidth permits. A device can burst up
to the Bc and still expect the data to get through. However, if long bursts persist, then a higher CIR should
be purchased. Be describes the bandwidth available above the CIR up to the access rate of the link. Be is
not negotiated, frames may be transmitted at this level but are most likely dropped.
20. What happens when the DCE sets the BECN bit to 1?
The sending device is notified of congestion on the network in hopes it will reduce flow of frames.
21. What happens when the DCE sets the FECN bit to 1?
The destination device is notified of congestion on the network.
22. What happens when the DCE sets the DE bit to 1?
When there is congestion, these frames will be dropped first.
23. Complete Activity 4.1.3.5 – Identify Frame Relay Bandwidth and Flow Control Terminology
24. Identify the parts in bold of the static frame relay map:
R1(config-if)#frame-relay map ip 200.10.5.1 220
Protocol
Destination IP
Address
Local DLCI
25. What is the Split Horizons rule?
A routing update cannot be forwarded out the interface it was received on.
26. What three ways can routing reachability issues be resolved?
Disable split horizons, use a fully meshed topology, configure subinterfaces on the hub router.
27. Describe Multipoint Subinterfaces:
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Act as NBMA so they do not resolve the split horizon issues
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Can save address space because it uses a single subnet
28. List the two step command to configure a point-to-point subinterface on the Serial 0/0/0 interface with
DCLI 100:
R1(config-if)#int serial 0/0/0.100 point-to-point
R1(config-subif)#frame-relay interface-dlci 100
29. Complete Activity 4.2.2.5 – Match Frame Relay Reachability Terms to Descriptions
30. What command should be used at each step when verifying frame relay operation?
a. Look at interfaces - show interfaces
b. LMI Statistics - show frame-relay lmi
c. PVC status - show frame-relay pvc
d. Clear frame relay maps – show frame-relay map and clear frame-relay inarp