2013 Latest Cisco 350-001 Exam Section 1: Frame Relay (10 Questions)
QUESTION NO: 1
Routers TK1, TK2, and TK3 are configured in a hub and spoke frame relay environment,
with router TK1 as the hub. You have configured Router TK1, Router TK2, and Router
TK3 to run IGRP over the frame relay connections. No sub-interfaces are used. You have
configured a single IP subnet on all the Frame Relay interfaces. Router TK1 can reach
both router TK2 and TK3, but TK2 and TK3 can not reach each other.
What is the probable cause of this problem?
A. Router TK1 is missing frame maps.
B. Router TK2 and Router TK3 are not performing frame map updates.
C. LMI mismatches between routers TK2 and TK3.
D. Split-horizon is enabled on Router TK1.
E. Split-horizon is disabled on Router TK1.
The rule of split horizons is the problem with distance vector protocols such as IGRP. The split horizon rule prohibits a router from advertising a route through an interface that the router itself uses to reach that destination. Without sub-interfaces, split-horizon goes into effect, and all routes learned from the Serial interface will not be advertised out of that interface. Incorrect Answers: A, B. If the problem was related to missing frame maps or missing updates, then any given location would have issues reaching any location. In this case, router TK2 and TK3 are both able to reach TK1 with no problems.
QUESTION NO: 2
You are troubleshooting a frame relay problem with the serial0 interface on one of your TestKing routers. When the interface is brought up, it stays up for a short time before it goes back down. You issue the show interface command, and from this you can see that your interface shows LMI status messages sent, but none received. What could be the problem?
A. There are too many input errors on the line.
B. The Frame-Relay lmi-type is set incorrectly.
C. Too many sub-interfaces are exceeding IDB limits.
D. The DCD not set correctly for a Frame-Relay circuit.
E. Keepalives are not set correctly on both ends.
In a frame relay configuration, the router’s interface always assumes that the connection is up first. Only after missing three consecutive LMI status messages will the interface go down. This explains why the interface shows an “up” status for a short time before going back down. In this case the counters for LMI sent is increasing while the counters for LMI rcvd is still 0. This clearly indicates a case of misconfigured LMI type. For a detailed discussion on how to troubleshoot serial lines, refer the link below.
C. IDB units are Individual Data Blocks, which are units that consume memory resources
for each sub-interface that is created. In order to surpass the IDB limits of most routers,
thousands of sub-interfaces will need to be created. In addition, after this threshold is met,
no more sub-interfaces can be created. Since this question is referring to an already
configured router, this is not the problem.
D, E. Although both of these issues could cause problems with the serial lines staying up,
they do not explain the fact that LMI status inquiries are received back. Even with
keepalives or DCD information set incorrectly, the LMI messages should still be sent and
QUESTION NO: 3 The TestKing WAN consists of a frame relay network using ANSI LMI. What is the maximum theoretical number of DLCI’s that can be advertised on a Frame-Relay interface with an MTU of 1500 bytes when using ANSI LMI?
The formula for finding the maximum number of DLCI’s for ANSI is (1500-13)/5=max DLCIs = 297.4. See below for the specifics for how this formula is generated: Analysis In a PVC information packet, the Report Type (RT) portion is one byte long and the KeepAlive (KA) portion is two bytes long. For the ANSI and Q933a LMIs, the PVC information is 3 bytes long, whereas for the Cisco LMI it is 6 bytes long due to the additional “bw” (for BandWidth) value. The “bw” value represents the Committed
configured to forward this information.
The static overhead in each case is 13 bytes [Entire LMI packet minus IEs (10 bytes) +
RT (1 byte) + KA (2 bytes)]. We can subtract this number from the Maximum
Transmission Unit (MTU) to get the total available bytes for DLCI information. We then
divide that number by the length of the PVC IE (5 bytes for ANSI and Q933a, 8 bytes for
Cisco) to get the maximum theoretical number of DLCIs for the interface:
For ANSI or Q933a, the formula is: (MTU – 13) / 5= max DLCIs.
For Cisco, the formula is (MTU – 13) / 8= max DLCIs.
QUESTION NO: 4 The Testking frame relay network is displayed in the diagram below, along with the partial configuration of router TK1:
What command must be added to interface serial 0/0 of TK1 to allow it to ping TK3?
A. frame-relay inverse-arp ip
B. frame-relay interface-dlci 302
C. encapsulation frame-relay ietf
D. frame-relay map ip 192.168.1.3 102 broadcast
E. None of the above
The frame relay map command is used to map layer 3 addresses to layer 2 DLCI information. In this case, the router TK1 is configured to statically map IP address
192.168.1.3 to DLCI 102.
A. Inverse ARP creates dynamic address mappings, as contrasted with the frame-relay map command, which defines static mappings between a specific protocol address and a specific DLCI. In this case, there is not a PVC that directly connects TK1 and TK3, so Inverse ARP alone will not be sufficient.
B. This command should be used on point to point subinterfaces, not on the physical serial interface because it will map all IP addresses to the 302 DLCI, which is incorrect.
C. This command should be used to connect a Cisco router to a non-Cisco frame relay router.
QUESTION NO: 5 The TK1 frame relay router is configured for frame relay traffic shaping as shown in the diagram below:
ip address 192.168.1.1 255.255.0
frame-relay interface-dlci 101
map-class frame-relay ccie
frame-relay cir 128000
frame-relay bc 16000
frame-relay be 0
frame-relay adaptive-shaping becn
Router TK1 is receiving BECNs. What is the lowest rate TK1 will shape its output traffic to?
A. 0 kbps
B. 16 kbps
C. 64 kbps
D. 128 kbps
E. 384 kbps
The minimum CIR is value is specified by the “frame-relay mincir” command. This command is optional, and if it is omitted from the configuration, the default value is found by dividing the CIR value that is specified by two. In this specific example, it is 128000/2 for a minimum value of 64 kbps, so choice C is correct. Some additional information on Frame Relay Adaptive Traffic Shaping can be found below: The Adaptive Frame Relay Traffic Shaping for Interface Congestion feature enhances Frame Relay traffic shaping functionality by adjusting permanent virtual circuit (PVC) sending rates based on interface congestion. When this new feature is enabled, the traffic-shaping mechanism monitors interface congestion. When the congestion level exceeds a configured value called queue depth, the sending rate of all PVCs is reduced to the minimum committed information rate (minCIR). As soon as interface congestion drops below the queue depth, the traffic-shaping mechanism changes the sending rate of the PVCs back to the committed information rate (CIR). This process guarantees the minCIR for PVCs when there is interface congestion.
NoteThe sum of the minCIR values for all PVCs on the interface must be less than the usable interface bandwidth. This new feature works in conjunction with backward explicit congestion notification (BECN) and Foresight functionality. If interface congestion exceeds the queue depth when adaptive shaping for interface congestion is enabled along with BECN or ForeSight, then the PVC sending rate is reduced to the minCIR. When interface congestion drops below the queue depth, then the sending rate is adjusted in response to BECN or ForeSight. Reference: http://www.cisco.com/en/US/products/sw/iosswrel/ps1839/products_feature_guide09186a0080087b91.htm
QUESTION NO: 6
The TestKing frame relay network is shown in the display below:
At which interfaces can the DE bit be set for frame relay packets flowing from TK1 to TK2? (Select all that apply)
Answer: A, B, C, D Explanation
The frame relay provider’s backbone is shared by many users and possibly multiple services. To keep you (and everybody else) from sending more data than the network can hold, frames sent above your contracted rate may be marked as Discard Eligible (DE). DE bits are set by the carrier network, not your equipment. They are also an indication of congestion within the frame relay network, so the DE bits are set on the interior of the carrier network, not at the provider edge to customer edge portion. If your equipment receives DE-marked frames, this indicates that data sent at this rate in the future may get dropped. This may be an early indicator of traffic rates that you didn’t plan for in the design of your frame relay WAN.
Frame relay equipment notices congestion when it sees frames marked with the Forward
Error Correction Notification (FECN) and Backward Error Correction (BECN) bits.
These merely indicate an overload within the carrier network, and are only of value in
monitoring the carrier’s health.
The Cisco router can be configured to mark packets as DE using the “frame-relay de-list”
command, making choice A also correct.
E: The DE bits are set between the carrier’s frame relay switches, not between the frame relay switches and the customer provided routers. The DE frames are also used only within the network provider, so they would not be marked on interface E since the frame is going directly to the customer router.
QUESTION NO: 7
The TestKing frame relay network is depicted below:
Traffic from TestKing1 to TestKing2 is experiencing congestion. What device sets the BECN bit?
A. TestKing1 sets the BECN bit on outgoing packets.
B. TestKing2 sets the BECN bit on outgoing packets.
C. SwB sets the BECN bit on packets from TestKing1 to TestKing2.
D. SwB sets the BECN bit on packets from TestKing2 to TestKing1.
If device A is sending data to device B across a Frame Relay infrastructure and one of the intermediate Frame Relay switches encounters congestion, congestion being full buffers, over subscribed port, overloaded resources, etc, it will set the BECN bit on packets being returned to the sending device and the FECN bit on the packets being sent to the receiving device. This has the effect of telling the sending router to Back off and apply flow control like traffic Shaping and informs the receiving device that the flow is congested and that it should inform upper layer protocols, if possible, that it should close down windowing etc to inform the sending application to slow down. A FECN tells the receiving device that the path is congested so that the upper layer protocols should expect some delay. The BECN tells the transmitting device that the Frame Relay network is congested and that it should “back off” to allow better throughput. FECN (Forward Error Congestion Notification) BECN (Backward Error Congestion Notification) Reference: http://www.sins.com.au/network/frame-relay-fecn-becn.html
QUESTION NO: 8
The TestKing frame relay network is displayed in the following diagram:
What command must be added to interface serial 0/0 of TestKing1 to allow it to ping the TestKing3 remote site?
A. frame-relay inverse-arp ip
B. framy-relay interface-dlci 302
C. encapsulation frame-relay ietf
D. frame-relay map ip 192.168.1.3 102 broadcast
E. frame-relay map ip 192.168.1.3 302 broadcast
Connecting from Spoke to Spoke: You cannot ping from one spoke to another spoke in a hub and spoke configuration using multipoint interfaces because there is no mapping for the other spokes’ IP addresses. Only the hub’s address is learned via the Inverse Address Resolution Protocol (IARP). If you configure a static map using the frame-relay map command for the IP address of a remote spoke to use the local data link connection identifier (DLCI), you can ping the addresses of other spokes. The local DLCI should be specified when using the “frame-relay map” command, which is 102 in this example.
Configuration:Prasit prasit#show running-configinterface Ethernet0ip address 188.8.131.52 255.255.255.0!interface Serialip address 184.108.40.206 255.255.255.0encapsulation frame-relayframe-relay map ip 220.127.116.11 150frame-relay interface-dlci 150 Reference: http://www.cisco.com/en/US/tech/tk713/tk237/technologies_tech_note09186a008014f8a7.shtml
QUESTION NO: 9 SplitHorizon is often used with Poison Reverse to prevent routing loops. Of the following choices, which statement is FALSE regarding the rule of Split Horizon?
A. It can cause problems on cetain Frame-Relay Hub-and Spoke configurations.
B. It is enabled by default on multipoint Frame-Relay subinterfaces.
C. It can be disabled for IP/RIP and IPX/RIP.
D. It aids in preventing routing loops.
E. None of the above.
For both point to point and point to multipoint sub-interfaces, split horizon is disabled by default. For physical serial frame relay multipoint interfaces, it is enabled by default. Frame Relay subinterfaces provide a mechanism for supporting partially meshed Frame
A can talk to station B, and station B can talk to station C, then station A should be able to talk to station C directly. This is true on LANs, but is not true on Frame Relay networks unless A is directly connected to C. Additionally, certain protocols such as AppleTalk and transparent bridging could not be supported on partially meshed networks because they require “split horizon,” in which a packet received on an interface cannot be transmitted out the same interface even if the packet is received and transmitted on different virtual circuits. By configuring Frame Relay subinterfaces, a single physical interface is treated as multiple virtual interfaces. This allows us to overcome split horizon rules. Packets received on one virtual interface can now be forwarded out another virtual interface, even if they are configured on the same physical interface. Subinterfaces address these limitations by providing a way to subdivide a partially meshed Frame Relay network into a number of smaller, fully meshed (or point-to-point) subnetworks. Each subnetwork is assigned its own network number and appears to the protocols as if it is reachable through a separate interface. (Note that point-to-point subinterfaces can be unnumbered for use with IP, reducing the addressing burden that might otherwise result.) IP RIP can indeed have split horizon disabled. This can be accomplished via the use of sub-interfaces, or with the “no ip split-horizon” interface command. This will disable split horizons for IP traffic, including RIP. However, IPX RIP traffic can not be disabled so this statement is false.
A: This statement is true. For networks using distance vector routing protocols, spoke site to spoke site connectivity can be affected due to the split horizon rule.
B: Cisco serial interfaces are multipoint interfaces by default unless specified as a point-to-point subinterface. Though less common than point-to-point subinterfaces, it is possible to divide the interface into separate virtual multipoint subinterfaces.
Multipoint interfaces/subinterfaces are still subject to the split-horizon limitations as discussed above.
All nodes attached to a multipoint subinterface belong to the same network number. Typically, multipoint subinterfaces are used in conjunction with point-to-point interfaces in cases where an existing multipoint frame relay cloud is migrating to a subinterfaced point-to-point network design. A multipoint subinterface is used to keep remote sites on a single network number while slowly migrating remote sites to their own point-to-point subinterface network.
D: Routing loop prevention is the reason why split horizon was created.
QUESTION NO: 10 On router TK1, you want to view the status of a frame relay connection. Which “show” commands will display the status of a Frame-Relay PVC? (Select all that apply)
A. show frame relay pvc
B. show frame-relay pvc
C. show frame-relay interface
D. show frame-relay lmi
E. show frame-relay map
F. show frame relay interface
Answer: B, E
The following is the example output from the show frame-relay pvc command, which explicitly displays the PVC status: TK1#show frame-relay pvc
PVC Statistics for interface Serial0 (Frame Relay DCE)
Active Inactive Deleted Static
Local 1 0 0 0
Switched 0 0 0 0
Unused 0 0 0 0
DLCI = 101, DLCI USAGE = LOCAL, PVC STATUS = ACTIVE, INTERFACE = Serial0
input pkts 207 output pkts 239 in bytes 15223
out bytes 14062 dropped pkts 0 in FECN pkts 0
in BECN pkts 0 out FECN pkts 0 out BECN pkts 0
in DE pkts 0 out DE pkts 0
out bcast pkts 17 out bcast bytes 3264
PVC create time 00:11:32, last time PVC status changed 00:11:32
Similarly, for show frame-relay map:
TK1#show frame-relay map
Serial3/1/0.100(D1) (up): point-to-point(D2) dlci, dlci
status defined, active(D5)
Serial3/1/0.120 (up): point-to-point dlci, dlci 402(0x192,0x6420),
status defined, active
A: This is an invalid command, as the Cisco IOS syntax uses frame-relay, not frame relay.
C: The “show frame-relay interface resource” command is a FR to ATM internetworking command that will show PVC stats for Cisco ATM switches. It is not really a valid router IOS command, and it does not show the status of the individual PVC’s
D: The following is sample output from the show frame-relay lmi command when the interface is a data terminal equipment (DTE) device: TK1# show frame-relay lmi
LMI Statistics for interface Serial1 (Frame Relay DTE) LMI TYPE = ANSI Invalid Unnumbered info 0 Invalid Prot Disc 0 Invalid dummy Call Ref 0 Invalid Msg Type 0 Invalid Status Message 0 Invalid Lock Shift 0 Invalid Information ID 0 Invalid Report IE Len 0 Invalid Report Request 0 Invalid Keep IE Len 0 Num Status Enq. Sent 9 Num Status msgs Rcvd 0 Num Update Status Rcvd 0 Num Status Timeouts 9
None of the fields above explicitly show the status of the the PVC.
F: This is an invalid command
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