CCNA – WAN 2
Here you will find answers to WAN Questions – Part 2
If you are not sure about Frame Relay, please read my Frame Relay tutorial.
Question 1
Users have been complaining that their Frame Relay connection to the corporate site is very slow. The network administrator suspects that the link is overloaded. Based on the partial output of the Router#show frame relay pvc command shown in the graphic, which output value indicates to the local router that traffic sent to the corporate site is experiencing congestion?
A. DLCI=100
B. last time PVC status changed 00:25:40
C. in BECN packets 192
D. in FECN packets 147
E. in DF packets 0
Answer: C
Explanation
First we should grasp the concept of BECN & FECN through an example:
Suppose Router A wants to send data to Router B through a Frame Relay network. If the network is congested, Switch 1 (a DCE device) will set the FECN bit value of that frame to 1, indicating that frame experienced congestion in the path from source to destination. This frame is forwarded to Switch 2 and to Router B (with the FECN bit = 1).
Switch 1 knows that the network is congesting so it also sends frames back to Router A with BECN bit set to 1 to inform that path through the network is congested.
In general, BECN is used on frames traveling away from the congested area to warn source devices that congestion has occurred on that path while FECN is used to alert receiving devices if the frame experiences congestion.
BECN also informs the transmitting devices to slow down the traffic a bit until the network returns to normal state.
The question asks “which output value indicates to the local router that traffic sent to the corporate site is experiencing congestion” which means it asks about the returned parameter which indicates congestion -> BECN.
Question 2
When troubleshooting a Frame Relay connection, what is the first step when performing a loopback test?
A. Set the encapsulation of the interface to HDLC.
B. Place the CSU/DSU in local-loop mode.
C. Enable local-loop mode on the DCE Frame Relay router.
D. Verify that the encapsulation is set to Frame Relay.
Answer: A
Explanation
The first thing when performing a loopback test on a Frame Relay connection is to reconfigure the encapsulation of the interface to HDLC protocol instead of Frame Relay protocol. The main reason is Frame Relay requires a pair of DCE/DTE which cannot be used in a loopback test.
For more information about steps of trouble shooting Frame Relay, please read: http://www.cisco.com/en/US/tech/tk713/tk237/technologies_tech_note09186a008014f8a7.shtml#topic20
For your information, below is a paragraph quoted from the above link:
“Serial0 is down, line protocol is down”
This output means you have a problem with the cable, channel service unit/data service unit (CSU/DSU), or the serial line. You need to troubleshoot the problem with a loopback test. To do a loopback test, follow the steps below:
1. Set the serial line encapsulation to HDLC and keepalive to 10 seconds. To do so, issue the commands encapsulation hdlc and keepalive 10 under the serial interface.
2. Place the CSU/DSU or modem in local loop mode. If the line protocol comes up when the CSU, DSU or modem is in local loopback mode (indicated by a “line protocol is up (looped)” message), it suggests that the problem is occurring beyond the local CSU/DSU. If the status line does not change states, there is possibly a problem in the router, connecting cable, CSU/DSU or modem. In most cases, the problem is with the CSU/DSU or modem.
3. Ping your own IP address with the CSU/DSU or modem looped. There should not be any misses. An extended ping of 0×0000 is helpful in resolving line problems since a T1 or E1 derives clock from data and requires a transition every 8 bits. B8ZS ensures that. A heavy zero data pattern helps to determine if the transitions are appropriately forced on the trunk. A heavy ones pattern is used to appropriately simulate a high zero load in case there is a pair of data inverters in the path. The alternating pattern (0×5555) represents a “typical” data pattern. If your pings fail or if you get cyclic redundancy check (CRC) errors, a bit error rate tester (BERT) with an appropriate analyzer from the telco is needed.
4. When you are finished testing, make sure you return the encapsulation to Frame Relay.
Question 3
What occurs on a Frame Relay network when the CIR is exceeded?
A. All TCP traffic is marked discard eligible.
B. All UDP traffic is marked discard eligible and a BECN is sent.
C. All TCP traffic is marked discard eligible and a BECN is sent.
D. All traffic exceeding the CIR is marked discard eligible.
Answer: D
Explanation
Committed information rate (CIR): The minimum guaranteed data transfer rate agreed to by the Frame Relay switch. Frames that are sent in excess of the CIR are marked as discard eligible (DE) which means they can be dropped if the congestion occurs within the Frame Relay network.
Note: In the Frame Relay frame format, there is a bit called Discard eligible (DE) bit that is used to identify frames that are first to be dropped when the CIR is exceeded.
Question 4
What are two characteristics of Frame Relay point-to-point subinterfaces? (Choose two)
A. They create split-horizon issues.
B. They require a unique subnet within a routing domain.
C. They emulate leased lines.
D. They are ideal for full-mesh topologies.
E. They require the use of NBMA options when using OSPF.
Answer: B C
Question 5
The output of the show frame-relay pvc command shows ”PVC STATUS=INACTIVE”. What does this mean?
A. The PVC is configured correctly and is operating normally,but no data packets have been detected for more than five minutes.
B. The PVC is configured correctly, is operating normally and is no longer actively seeking the address the remote route,
C. The PVC is configured correctly, is operating normally and is waiting for interesting to trigger a call to the remote router.
D. The PVC is configured correctly on the local switch, but there is a problem on the remote end of the PVC.
E. The PVC is not configured on the switch.
Answer: D
Explanation
The PVC STATUS displays the status of the PVC. The DCE device creates and sends the report to the DTE devices. There are 4 statuses:
+ ACTIVE: the PVC is operational and can transmit data
+ INACTIVE: the connection from the local router to the switch is working, but the connection to the remote router is not available
+ DELETED: the PVC is not present and no LMI information is being received from the Frame Relay switch
+ STATIC: the Local Management Interface (LMI) mechanism on the interface is disabled (by using the “no keepalive” command). This status is rarely seen so it is ignored in some books.
Question 6
Which encapsulation type is a Frame Relay encapsulation type that is supported by Cisco routers?
A. Q933-A Annex A
B. IETF
C. ANSI Annex D
D. HDLC
Answer: B
Explanation
Cisco supports two Frame Relay encapsulation types: the Cisco encapsulation and the IETF Frame Relay encapsulation, which is in conformance with RFC 1490 and RFC 2427. The former is often used to connect two Cisco routers while the latter is used to connect a Cisco router to a non-Cisco router. You can test with your Cisco router when typing the command Router(config-if)#encapsulation frame-relay ? on a WAN link. Below is the output of this command (notice Cisco is the default encapsulation so it is not listed here, just press Enter to use it).
Note: Three LMI options are supported by Cisco routers are ansi, Cisco, and Q933a. They represent the ANSI Annex D, Cisco, and ITU Q933-A (Annex A) LMI types, respectively.
HDLC is a WAN protocol same as Frame-Relay and PPP so it is not a Frame Relay encapsulation type.
Question 7
Router A is unable to reach Router B. Both routers are running ios version 12.0. After reviewing the command output and graphic, what is the most likely cause of the problem?
A. incorrect bandwidth configuration
B. incorrect LMI configuration
C. incorrect map statement
D. incorrect IP address
Answer: C
Explanation
With this topology and the DLCI, we can only think of “incorrect map statement”. From the topology we can deduce traffic with a DLCI of 75 will be sent to 192.168.2.1 but the text below wrongly shows “DLCI 50″ for the next router 192.168.2.1 -> C is correct.
@9tut:
thx
@9tut,
is IETF encapsulation type not supported by frame relay?
@9tut, same question as with moloy. Encountered that problem before just cant recall if its in netad and the answer is IETF.
@9tut
Which encapsulation type is a Frame Relay encapsulation type that is supported by Cisco routers?
A. Q9333-A Annex A
B. IETF
C. ANSI Annex D
D. HDLC
Three LMI options are supported by Cisco routers: ansi, Cisco, and q933a. Encapsulation are Cisco & IETF.
But Ans choosed as ANSI (c).
It is a mistake, I updated Question 6 answer. Thanks for your detection!
@9tut
Just want to clarify on question no.2. for conducting loopback test for frame relay, here at our company when we conduct Loop back test we removed Keepalives for frame relay encap. Please clarify on this. Im not saying that the answer is wrong, Im just confused, because when we changed encap from FR to HDLC, the subinterface for that circuit will be removed. please advise. Thank You…
@Brando: We change the encapsulation from FR to HDLC to make sure layer 1 & layer 2 are working correctly so we don’t need the subinterface here. Maybe we will need to reconfigure the subinterfaces again.
Maybe your company does not want to delete the Frame Relay configuration so they keep it and remove keepalives. Here is the link related to the keepalives in Frame Relay, hope it help!
http://www.cisco.com/en/US/docs/ios/12_0t/12_0t5/feature/guide/FRKeep.html
640-802 exam is really difficult…dnt take it easy..
failed today..!!
Really awesome articles here. I will do CCNA this monday and this really help me.
Thanks!!!
please ans. 6 is ietf or ansi ??
i think its ietf
google you lazy…
Hi, could someone explain the answers to Q4 for me please?
Especially : ‘They require a unique subnet within a routing domain.’
Thanks
Matt ,
read frame relay tutorial
I had Question 6 in my exam last week.
@Matt, yes any interface on a router whether physical or subinterface should be in a different subnet from other router interfaces thats where they are coming from.
That was the best BECN/FECN explanation I’ve seen yet. Thank you!
Regarding the IETF question, I was thrown off initially, too. I expected to see an encapsulation option of CISCO. Then I realized that Cisco still supports the nonCisco Router BY using IETF.
Good luck on your exam everyone. Mine is either this Friday or Monday. I’m feeling confident!
God Bless 9tut!
Great stuff, good studying
for question :6 Answer is IETF
@9tut
i have this question from the dump…
The serial0/0 interface of the Tampa router connects the Oriando router.Which two statements are true about the connection between these two routers?(choose two)
A.The only device with which the Tampa router will negotiate a data link is the Orlando router.
B.The link is addressed on the *zero*subnet 10.0.0.0 network.
C.The link uses a three-way handshake for authentication.
D.The link uses a two-way handshake for authentication.
E.Data exchanges between the Oriando and Tampa routers are encrypted
I think the answers are C & A ??
Hey guys, so can anyone tell me if I practise these sims and these questions, ill pass the exam?? I know my stuff as well but still just checking…. Please let me know,, thanks!!!
rye
yes A,C correct
m not able to understand Q.1. plz help me out.
@ccna pal
Q1. Is describing the mechanism frame-relay applies when there is congestion in the path or network during transmitting or receiving. And utilizes the term BECN which stands for Backward Explicit Congestion Notification during transmission, and FECN which stands for Forward Explicit Congestion Notification during receiving.
When there is congestion during transmission, the switch(DCE Device) sets BECN to 1, and sends it to the transmitting router, and also if there is congestion during receiving, the switch(DCE Device) setsFECN to 1, and send it to the receiving router. This is some form of notification to the sender and the receiver.
When you do a “show frame-relay pvc” command, you will see the values of BECN and FECN.
At some point in time the BECN values informs the transmitting router to slow down the traffic until the path or network returns to normal state.
I hope this piece of breakdown in addition to the explanation given above is helpful. Thanks.
planning to take exam on tomorrow morning……any unexpected recent changes in ccna exam…can anyone help??
Which encapsulation type is a Frame Relay encapsulation type that is supported by Cisco routers?
A. Q933-A Annex A
B. IETF
C. ANSI Annex D
D. HDLC
i think Ans………. D:hdlc
replay Ans
@naveed khan
read explanation provided by 9tut.
also read a bit here too:
http://www.mcmcse.com/cisco/guides/frame_relay_encapsulation_types.shtml
no naveed….i think answer is B….correct me if it is wrong…
@naveed
Frame relay encapsulation is a subset of HDLC encapsulation but it does not mean its one of the encapsulation it uses.
I’m not sure if i understand uat r u talking about Franco. Anyway, Naveed the answer is B (IETF)….check this out..is god itself talking…..
“When you configure Frame Relay, you specify an encapsulation of Frame Relay. But unlike HDLC or PPP, with Frame Relay, there are two encapsulation types: Cisco and IETF (Internet Engineering Task Force).”
Amen Todd!! o:)
@Cac0 @naveed
I thought naveed doubts came from the origin of frame relay encapsulation which is a derivative of HDLC encapsulation, as we all know, but it does not mean FR supports HDLC encapsulation. In cisco routers FR support cisco and IETF only, the following output taken from a cisco router supports this statement:
Router(config-if)#encapsulation frame-relay ?
ietf Use RFC1490/RFC2427 encapsulation
the default is cisco encapsulation and you can adjust to IETF if you are to connect to an another vendor device.
Again, I’m not sure about that. I think you’re confused. Frame Relay comes from X.25 technologie. HDLC is a totally diferent L2 encapsulation for synchronous serial links. Again, Todd says:
“Frame Relay has at its roots a technology called X.25, and it essentially incorporates the components of X.25 that are still relevant to today’s reliable and relatively “clean” Tecommunications networks while leaving out the no-longer-needed error-correction components.”
You tell me…!!! \o/
And there is where yo are mistaken my friend FR encapsulation is a derivative of HDLC
“…The Frame Relay frame is a subset of the HDLC frame type. Therefore, it is delimited with flag fields. The 1-byte flag uses the bit pattern 01111110…” CCNA Exploration Accessing the WAN Chapter 3, page 3.1.3.1 (cisco certified)
The concept of a FR network is a derivative of X.25, we must remember that this technology was not referenced in the OSI model nor TCP/IP therefore its encapsulation did not obey theses stacks that FR does.
I am telling you!! /
Thanks 9tut
send me latest dump plz
hossam.saber4@gmail.com
thanks in advance
today i passed ccna with 900 one question from frame relay
how to view encapsulation (cisco or ietf) in frame relay
is the exam has 1000 question?how they score the correct answer?
Can you please send me CCNA ICND2 dump at rizeed@gmail.com. PLEASE urgently..
thx 9tut , can u please send me the latest ccna dumps on midomashakel_11@hotmail.com , thx sooooo much
I need help please send me latest ccna dumps that i can trust at luckyparshad@yahoo.com
Hi 9tut/anji pls send me latest dump if u have any
my email id is samyak1985@gmail.com
Hi guys, i am very appreciate what you doing. i will take my CCNA on February 17th, could you please send me the last dump? thank you in advance.
my email is noelkenson@gmail.com
which command is used sh which encapsulation is used in frame relay(ietf,cisco)?
sh frame relay lmi or sh frame relay map
which command is used sh which encapsulation is used in frame relay(ietf,cisco)?
sh frame relay lmi or sh frame relay map or sh interfaces serial
i think i got answer but pls check its right….
show interface serial interface-type number
The show interface serial privileged EXEC mode command displays detailed information of a physical interface or a subinterface. The information shown by the show interface serial command offers the following information on Frame Relay:
The type of Frame Relay encapsulation used on an interface or PVC
The keepalive interval configured
The Frame Relay LMI type used
The status of Frame Relay LMI
Information on whether the interface is configured as a Frame Relay DTE or a DCE device
Hi 9tut… Hi Guys! Can you please help me… I will take exam this Feb. Please send me latest dump so that I will have an idea for the exam.. rico.blake@ymail.com
Thanks Guys!
Hi everyone, can anyone help me please.. I’ll be having my exam this feb 15. Please send me the latest dump of the exam if you have. Appreciate much.
Hi everyone, can anyone help me please.. I’ll be having my exam this feb 15. Please send me the latest dump of the exam if you have. Appreciate much. here is my email add: dlanz19@yahoo.com
Thanks 9 tut I passed 982 today
EIGRP ACL vlan&vtp
Hi Emad…it that the SIM test?it is same in SIM at here?
why in a trame hdlc,ppp or frame relay , they don’t have a mac address destintion or source ?
latest dumps :-
http://www.examcollection.com/cisco/Cisco.PrepKing.640-802.v2012-01-03.by.DHARANI.615q.vce.file.html
&
http://www.examcollection.com/cisco/Cisco.Acme.640-802.v2011-07-09.by.Collisio.486q.vce.file.html