CCNA 640-802 Questions/Answers

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Oct 24, 2013 (3 years and 11 months ago)

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CCNA 640-802 Questions/Answers – WAN


2013 1


At which layer of the OSI model Frame Relay operate? (Choose two)
A. Application
B. Network
C. Data Link
D. Transport
E. Presentation
F. Physical

Answer: C, F
Frame Relay is a popular high performance WAN protocol that operates at the physical and data link
layers of the OSI reference model. Frame relay is a type of WAN connection use to connect one site to
many remote sites through a single physical circuit; this operation makes it easy to construct reliable and
inexpensive networks.
Frame Relay network is very simple. Frame Relay connections are created by configuring network routers
or other devices to communicate with a service provider Frame Relay switch. The service provider
configures the Frame Relay switch, which helps keep end-user configuration tasks to a minimum.
Frame Relay has lower overhead than X.25 because it has fewer capabilities. For example, Frame Relay
does not provide error correction; modern WAN facilities offer more reliable connection services and a
higher degree of reliability than older facilities. The Frame Relay node simply drops packets without
notification when it detects errors. Any necessary error correction, such as retransmission of data, is left
to the endpoints. This makes propagation from customer end to customer end through the network very
fast.
Frame Relay network uses permanent virtual circuits (PVCs). PVC is the logical path along an originating
Frame Relay link, through the network, and along a terminating Frame Relay link to its ultimate
destination. Compare this to the physical path used by a dedicated connection. In a network with Frame
Relay access, PVC uniquely defines the path between two endpoints.
Each virtual circuit is identified by a Data Link Connection Identifier (DLCI), which is simply a number
between 0 and 1023. In fact, Cisco routers can only use DLCI numbers in the range 16 through 1007 to
carry user data.

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CCNA 640-802 Questions/Answers – WAN


2013 2


Which of the following protocols detects looped links?
A. CHAP
B. PAP
C. WEP
D. LCP
E. DLCI

Answer: D
LCP provides four notable features, summarized in following table. Feature list in the table is optional
and is disabled by default.


LCP notices looped links quickly using a feature called magic numbers. When using PPP, the router sends
PPP LCP messages instead of Cisco-proprietary keepalives across the link; these messages include a
magic number, which is different on each router. If a line is looped, the router receives an LCP message
with its own magic number instead of getting a message with the other router’s magic number. When a
router receives its own magic number, that router knows that the frame it sent has been looped back, so
the router can take down the interface, which speeds convergence.

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CCNA 640-802 Questions/Answers – WAN


2013 3



You need to configure Frame Relay multipoint subinterface that enables R3 to communicate with R1 and
R2. Routers are connected using 256 kbps link. Which commands need to be configured on R3?
A.
R3(config)#interface Serial3/1
R3(config-if)#no ip address
R3(config-if)#encapsulaion frame-relay
R3(config-if)#interface serial 3/1.301 point-to-point
R3(config-subif)#ip address 172.16.1.3 255.255.255.248
R3(config-subif)#frame-relay interface-dlci 103
R3(config-subif)#frame-relay interface-dlci 203
R3(config-subif)#bandwidth 256
B.
R3(config)#interface Serial3/1
R3(config-if)#no ip address
R3(config-if)#encapsulation frame-relay
R3(config-if)#interface serial 3/1.301 multipoint
R3(config-subif)#ip address 172.16.1.1 255.255.255.248
R3(config-subif)#ip address 172.16.1.2 255.255.255.248
R3(config-subif)#frame-relay interface-dlci 203
R3(config-subif)#frame-relay interface-dlci 103
R3(config-subif)#bandwidth 256
C.
R3(config)#interface Serial3/1
R3(config-if)#no ip address
R3(config-if)#encapsulation frame-relay
R3(config-if)#interface serial 3/1.301 point-to-point
R3(config-subif)#ip address 172.16.1.3 255.255.255.248
R3(config-subif)#frame-relay interface-dlci 301

CCNA 640-802 Questions/Answers – WAN


2013 4


R3(config-subif)#frame-relay interface-dlci 302
R3(config-subif)#bandwidth 256
D.
R3(config)#interface Serial3/1
R3(config-if)#no ip address
R3(config-if)#encapsulation frame-relay
R3(config-if)#interface serial 3/1.301 multipoint
R3(config-subif)#ip address 172.16.1.3 255.255.255.248
R3(config-subif)#frame-relay interface-dlci 301
R3(config-subif)#frame-relay interface-dlci 302
R3(config-subif)#bandwidth 256

Answer: D
Frame Relay subinterfaces can be configured to create PVC (Primary Virtual Circuit) connections
through a Frame Relay cloud. When configuring subinterfaces for Frame Relay you need to configure IP
address on the physical interface. This is achieved with no ip address command on particular physical
interface, because IP address will be assigned to the subinetraface.
To configure subinterface for Frame Relay you must associate DLCI (Data Link Connection Identifier)
with subinterface with frame-relay interface-dlci

command.
Another way is to associate DLCI with IP address with frame-relay map command, like follows:
R3(config)#interface Serial3/1
R3(config-if)#no ip address
R3(config-if)#encapsulation frame-relay
R3(config-if)#interface serial 3/1.301 multipoint
R3(config-subif)#ip address 172.16.1.3 255.255.255.248
R3(config-subif)#frame-relay map ip 172.16.1.1103
R3(config-subif)#frame-relay map ip 172.16.1.2203
R3(config-subif)#bandwidth 256
In point-to point subinterfaces each interface resides in different subnet. Point-to-point subinterface
configuration consists of only one PVC connection through the Frame Relay cloud.
In our case R1 and R2 need to be configured as follows:
R1(config)#interface Serial4/2
R1(config-if)#ip address 172.16.1.1 255.255.255.248
R1(config-if)#encapsulation frame-relay
R1(config-subif)# frame-relay map ip 172.16.1.2 103 broadcast

and

CCNA 640-802 Questions/Answers – WAN


2013 5


R2(config)#interface Serial3/0
R2(config-if)#ip address 172.16.1.2 255.255.255.248
R2(config-if)#encapsulation frame-relay
R2(config-subif)# frame-relay map ip 172.16.1.1 203 broadcast

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CCNA 640-802 Questions/Answers – WAN


2013 6


You want to connect remote office through 1.544 Mbps connection to WAN provider, from your
company router for data traffic. What should you configure to accomplish previous?
A. ATM
B. Frame Relay
C. X.25
D. Leased Line

Answer: B
Most efficient option for data traffic is Frame Relay. Frame Relay is packet switching technology for data
only, with medium speed requirements. Frame Relay allows multiple connections via virtual circuits
through single interface.
ATM (Asynchronous Transfer Mode) is high speed packet switching technology similar to Frame Relay.
ATM supports video and voice and data traffic. Most common ATM speed is 155 Mbps, and Gigabit
speed is used between ATM switches. Because these connections are more expensive than Frame Relay,
ATM is not cost efficient method for this connection speed.
X.25 operate at Network, Data Link and Physical Layer in OSI model. Because of that it is not efficient.
Leased lines work at Data link and Physical Layer of the OSI model and are used as end-user connections
between sites. To implement leased lines you have to purchase extra equipment, to support interface on
both sides of the link.

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CCNA 640-802 Questions/Answers – WAN


2013 7


Which command is used to configure WAN encapsulation on serial interface connected to T1 line?
(Choose three)
A. Router(config-if)#encapsulation hdlc
B. Router(config-if)#encapsulation frame-relay
C. Router(config-if)#encapsulation ppp
D. Router(config-if)#encapsulation chap
E. Router(config-if)#encapsulation pap

Answer: A, B, C
HDLC is WAN encapsulation method used by default for point-to-point serial links, from Cisco routers.
Frame-Relay is a WAN encapsulation method used for implementation of NBMA (Non-Broadcast
Multiaccess) network. Frame-Relay is Cisco-proprietary WAN encapsulation type. To configure Frame-
Relay between routers from different vendors you have to use IETF (Internet Engineering Task Force)
standard encapsulation type. To configure IETF encapsulation on Frame-Relay connection, you have to
use command:
Router(config-if)#encapsulation frame-relay ietf
PPP is WAN encapsulation method used for point-to-point serial links, between routers from different
vendors.










CCNA 640-802 Questions/Answers – WAN


2013 8


Regarding command Router(config-if)#ppp authentication chap pap, which of the following statements
are true? (Choose two).
A. Interface, on which this command is issued, must be connected to the neighboring switch.
B. Interface, on which this command is issued, is WAN interface.
C. CHAP authentication is allowed, PAP authentication refused on interface.
D. Both authentication methods are allowed and active on interface.
E. CHAP authentication will be allowed, but if remote device don’t support, then PAP authentication will
be attempted.

Answer: B, E
When you are creating a WAN link and also when the other end of a WAN link is NOT a Cisco router,
Point-to-Point Protocol can be used in synchronous, asynchoronous, HSSI, and ISDN links.
1. Get to the interface configuration mode and issue the following command,
Router(config-if)#encapsulation ppp
2. If you want to configure authentication (which is almost always the case), go through the following
steps:
- Choose the authentication type; Password Authentication Protocol (PAP), or Challenge Handshake
Authentication Protocol (CHAP).
Router(config-if)#ppp authentication XXX
where XXX is the authentication type which can be: pap, chap, pap chap, orchap pap. The last two
choices are to use the other authentication type when the first one fails.
CHAP is strongly recommended over PAP for two reasons. First, PAP sends the username and
password in plaintext, while CHAP sends hashed challenges only. Second is that CHAP does an
operation similar to periodic re-authentication in the middle of the communication session such that
it provides more security than PAP.
- Set a username and a password that the remote router would use to connect to your local router.
You can define many username-password pairs for many PPP connections to the same router.
Router(config)#username USER password PASS
, where USER is the host name of the remote router, and PASS is its password. Issue this command
once for each PPP connection. For example if you are connecting RouterA to RouterB and RouterC,
on RouterA issue this command once for each remote router.




CCNA 640-802 Questions/Answers – WAN


2013 9


Which statement is true about Point-to-Point Protocol? (Choose two)
A. PPP is Cisco proprietary protocol.
B. PPP will work between a Cisco router and a non-Cisco router.
C. PPP offers features like compression, multi-link and authentication (CHAP/PAP).
D. Protocols used by PPP at the Data Link layer are IP and IPX.

Answer: B, C
The Point-to-Point Protocol is another
Data Link layer
protocol that can be used to encapsulate data over
dedicated leased lines. PPP is also commonly used for dial-up connections to corporate networks and the
Internet. As such, PPP works over both synchronous and asynchronous serial interfaces. PPP is an IETF-
standard protocol capable of encapsulating a variety of upper-layer protocols including IP, IPX, and
AppleTalk to name but a few. It has largely replaced an earlier standard known as the Serial Link Internet
Protocol (SLIP). One of the main disadvantages of SLIP is that it only supports point-to-point
connections that use IP at the

PPP offers a wide variety of configurable options that make it a robust choice for encapsulating data over
leased lines. First and foremost, PPP supports authentication, which can be used to confirm the identity of
equipment or users at either end of a point-to-point connection. Both the Password Authentication
Protocol (PAP) and the Challenge Handshake Authentication Protocol (CHAP) can be used for
authentication on a Cisco router. PPP also supports a variety of data compression techniques including
Stacker, Predictor, and Microsoft Point-to-Point Compression (MPPC). Finally, PPP provides the ability
to combine multiple synchronous and asynchronous serial links such that they work as a single logical
connection, a technique referred to as PPP Multilink.
Network layer.
PPP is comprised of multiple protocols at the Data Link Layer, each with different areas of responsibility.
It can also run over a variety of different
physical layer
standards, although EIA/TIA-232 (formerly RS-
232) is the most commonly used. The ways in which the various PPP protocols and standards map to
the
OSI model is shown in the figure below.

CCNA 640-802 Questions/Answers – WAN


2013 10



Figure: Point-to-Point Protocol (PPP) protocols and standards as they relate to the OSI model.
The three protocols used by PPP at the Data Link layer are HDLC, the Link Control Protocol (LCP), and
various implementations of the Network Control Protocol (NCP). Each is described below.

HDLC. HDLC is the data framing method used over PPP links. In the case of PPP, the OSI
standard version is used rather than the Cisco proprietary version. This standardization helps to
ensure that PPP implementations by different vendors can communicate properly.

LCP. The Link Control Protocol is used for establishing, testing, configuring, and terminating
PPP connections. PPP options such as authentication, compression, and multilink are all
configured by LCP. The three main types of LCP frames used on a PPP connection are link-
establishment, link-maintenance, and link-termination.

NCP. Network Control Protocol frames are used to negotiate and configure the Network layer
protocols that can be used over a PPP session. For example, there are specialized NCPs for IP
(IPCP), IPX (IPXCP), AppleTalk (ATCP), and others. NCPs allow PPP to work in conjunction
with many Network layer protocols over the same link.

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CCNA 640-802 Questions/Answers – WAN


2013 11


You are configuring PPP serial link on your company router. You need to enable authentication for the
link with most secure authentication mechanism. Which commands are necessary to accomplish this?
A. Router(config)#int s0/1
Router(config-if)#encapsulation dot1q
Router(config-if)#ppp authentication pap
B. Router(config)#int s0/1
Router(config-if)#encapsulation hdlc
Router(config-if)#ppp authentication pap
C. Router(config)#int s0/1
Router(config-if)#encapsulation ppp
Router(config-if)#ppp authentication pap
D. Router(config)#int s0/1
Router(config-if)#encapsulation ppp
Router(config-if)#ppp authentication chap

Answer: D
PPP is WAN protocol used on Point-to-Point serial links. PPP supports both synchronous and
asynchronous communications. PPP supports two types of authentication: PAP (password Authentication
Protocol) and CHAP (Challenge Handshake Authentication Protocol). When PAP is used username and
password of the originating router are sent over the link in plain text. When CHAP is used, hash of user
name and password and random number are sent to the destination router; user name and password are
not swnd across the link as text. CHAP is more secure than PAP for authentication.
HDLC is used also for point-to-point serial links, but supports only synchronous communications.

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