Interconnecting Cisco Networking Devices Part 2 (ICND2 v3.0)
Question No: 151 DRAG DROP – (Topic 4)
1) a router is this type of device: DTE2) the most common type of virtual circuit: PVC3) provides status messages between DTE and DCE devices: LMI4) identifies the virtual connection between the DTE and the switch: DLCI
Configuring the LMI Type on a Frame Relay Interface http://www.ciscopress.com/articles/article.asp?p=170741amp;seqNum=3 Frame Relay DLCIs And Mappings http://www.mcmcse.com/cisco/guides/frame_relay_dlci.shtml
Question No: 152 – (Topic 4)
What does the frame-relay interface-dlci command configure?
local DLCI on the subinterface
remote DLCI on the main interface
remote DCLI on the subinterface
local DLCI on the main interface
Answer: A Explanation:
To assign a data-link connection identifier (DLCI) to a specified Frame Relay subinterface on the router or access server, or to assign a specific permanent virtual circuit (PVC) to a DLCI, or to apply a virtual template configuration for a PPP session, use the frame-relay interface-dlci interface configuration command
Example 4-23 Example of frame-relay interface-dlci Command and the Output of show frame-relay map
R4(config)#interface s1/2.403 point-to-point R4(config-subif)#frame-relay interface-dlci ?
lt;16-1007gt; Define a switched or locally terminated DLCI R4(config-subif)#frame-relay interface-dlci 403 ?
cisco Use CISCO Encapsulation
ietf Use RFC1490/RFC2427 Encapsulation
ppp Use RFC1973 Encapsulation to support PPP over FR protocol Optional protocol information for remote end
R4#show frame-relay map
Serial1/2.403 (up): point-to-point dlci, dlci 403(0xC9,0x3090), broadcast status defined, active
Question No: 153 – (Topic 4)
Which feature does PPP use to encapsulate multiple protocols?
Answer: A Explanation:
PPP permits multiple network layer protocols to operate on the same communication link. For every network layer protocol used, a separate Network Control Protocol (NCP) is provided in order to encapsulate and negotiate options for the multiple network layer protocols. It negotiates network-layer information, e.g. network address or compression options, after the connection has been established
Question No: 154 – (Topic 4)
Which two options are valid WAN connectivity methods? (Choose two.)
On each WAN connection, data is encapsulated into frames before itcrosses the WAN link. The following are typical WAN protocols:1. High-level Data Link Control (HDLC): The Cisco default encapsulation type onpoint-to-point connections, dedicated links, and circuit- switches connections.2. PPP: Provides router-to-router and host-to-network connections over synchronous andasynchronous circuits. PPP was designed to work with several network layer protocols,including IP.3. Frame-relay: A successor to X.25. This protocol is an industry-standard, switchesdata-link layer protocol that handles multiple virtual circuits
Question No: 155 – (Topic 4)
What are two characteristics of Frame Relay point-to-point subinterfaces? (Choose two.)
They create split-horizon issues.
They require a unique subnet within a routing domain.
They emulate leased lines.
They are ideal for full-mesh topologies.
They require the use of NBMA options when using OSPF.
Configuring Frame Relay Subinterfaces
On partially meshed Frame Relay networks, the problem of split horizon can be overcome by using Frame Relay subinterfaces. Frame Relay provides a mechanism to allow a physical interface to be partitioned into multiple virtual interfaces. In a similar way, using subinterfaces allows a partially meshed network to be divided into a number of smaller, fully meshed point-to-point networks. Generally, each point-to-point subnetwork is assigned a unique network address. This allows packets received on one physical interface to be sent out from the same physical interface, albeit forwarded on VCs in different subinterfaces.
There are two types of subinterfaces supported by Cisco routers: point-to-point and multipoint subinterfaces.
Question No: 156 – (Topic 4)
Which Layer 2 protocol encapsulation type supports synchronous and asynchronous circuits and has built-in security mechanisms?
Answer: B Explanation:
High-Level Data Link Control (HDLC) – HDLC is the default encapsulation type on point-to- point, dedicated links, and circuit-switched connections. It is used typically when communicating between two Cisco devices. It is a bit-oriented synchronous data link layer protocol.
Point-to-Point Protocol (PPP) – Provides router-to-router and host-to network connections over synchronous and asynchronous circuits. PPP was designed to work with several network layer protocols, such as IP, and IPX. PPP also has built in security mechanisms such as PAP and CHAP X.25/Link Access Procedure, Balanced (LAPB) – ITU-T standard that defines how connections between DTE and DCE are maintained for remote terminal access and computer communications in public data networks. X.25 specifies LAPB, a data line layer protocol. X.25 is a predecessor to Frame Relay.
Frame Relay – Industry standard, switched data link layer protocol that handles multiple virtual circuits. It is a next-generation to X.25 that is streamlined to eliminate some of the time-consuming processes (such as error correction and flow control) that were employed in X.25.
Question No: 157 – (Topic 4)
Which two statements about using the CHAP authentication mechanism in a PPP link are true? (Choose two.)
CHAP uses a two-way handshake.
CHAP uses a three-way handshake.
CHAP authentication periodically occurs after link establishment.
CHAP authentication passwords are sent in plaintext.
CHAP authentication is performed only upon link establishment.
CHAP has no protection from playback attacks.
Answer: B,C Explanation:
Understanding and Configuring PPP CHAP Authentication http://www.cisco.com/en/US/tech/tk713/tk507/technologies_tech_note09186a00800b4131. shtml
One-Way and Two-Way Authentication
CHAP is defined as a one-way authentication method. However, you use CHAP in both directions to create a two-way authentication. Hence, with two-way CHAP, a separate three-way handshake is initiated by each side. In the Cisco CHAP implementation, by default, the called party must authenticate the calling party (unless authentication is completely turned off). Therefore, a one-way authentication initiated by the called party is the minimum possible authentication. However, the calling party can also verify the identity of the called party, and this results in a two-way authentication.
One-way authentication is often required when you connect to non-Cisco devices.
Question No: 158 – (Topic 4)
The command frame-relay map ip 10.121.16.8 102 broadcast was entered on the router. Which of the following statements is true concerning this command?
This command should be executed from the global configuration mode.
The IP address 10.121.16.8 is the local router port used to forward data.
102 is the remote DLCI that will receive the information.
This command is required for all Frame Relay configurations.
The broadcast option allows packets, such as RIP updates, to be forwarded across the PVC.
Answer: E Explanation:
The command frame-relay map ip 10.121.16.8 102 broadcast means to map the remote IP 10.121.16.8 to the local DLCI 102. When the “broadcast” keyword is included, it turns Frame Relay network as a broadcast network, which can forward broadcasts.
Question No: 159 – (Topic 4)
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?
last time PVC status changed 00:25:40
in BECN packets 192
in FECN packets 147
in DF packets 0
Answer: C Explanation:
First we should grasp the concept of BECN amp; 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 -gt;BECN.
Question No: 160 – (Topic 4)
Refer to the exhibit.
What is the meaning of the term dynamic as displayed in the output of the show frame- relay map command shown?
The Serial0/0 interface is passing traffic.
The DLCI 100 was dynamically allocated by the router
The Serial0/0 interface acquired the IP address of 172.16.3.1 from a DHCP server
The DLCI 100 will be dynamically changed as required to adapt to changes in the Frame Relay cloud
The mapping between DLCI 100 and the end station IP address 172.16.3.1 was learned through Inverse ARP
Answer: E Explanation:
The term dynamic indicates that the DLCI number and the remote router IP address
172.16.3.1 are learned via the Inverse ARP process.
Inverse ARP is a technique by which dynamic mappings are constructed in a network, allowing a device such as a router to locate the logical network address and associate it with a permanent virtual circuit (PVC).