Implementing Cisco IP Routing (ROUTE v2.0)

 

QUESTION 11

A network administrator uses IP SLA to measure UDP performance and notices that packets on one router have a higher one-way delay compared to the opposite direction. Which UDP characteristic does this scenario describe?

 

A.

latency

B.

starvation

C.

connectionless communication

D.

nonsequencing unordered packets

E.

jitter

 

Correct Answer: A

Explanation:

Cisco IOS IP SLAs provides a proactive notification feature with an SNMP trap. Each measurement operation can monitor against a pre-set performance threshold. Cisco IOS IP SLAs generates an SNMP trap to alert management applications if this threshold is crossed. Several SNMP traps are available: round trip time, average jitter, one-way latency, jitter, packet loss, MOS, and connectivity tests.

Here is a partial sample output from the IP SLA statistics that can be seen:

router#show ip sla statistics 1

Round Trip Time (RTT) for Index 55

Latest RTT: 1 ms

Latest operation start time: *23:43:31.845 UTC Thu Feb 3 2005 Latest operation return code: OK

RTT Values:

Number Of RTT: 10 RTT Min/Avg/Max: 1/1/1 milliseconds Latency one-way time:

Number of Latency one-way Samples: 0

Source to Destination Latency one way Min/Avg/Max: 0/0/0 milliseconds Destination to Source Latency one way Min/Avg/Max: 0/0/0 milliseconds

Reference:

http://www.cisco.com/en/US/technologies/tk648/tk362/tk920/technologies_white_paper09186a008 02d5efe.html

 

 

QUESTION 12

Under which condition does UDP dominance occur?

 

A.

when TCP traffic is in the same class as UDP

B.

when UDP flows are assigned a lower priority queue

C.

when WRED is enabled

D.

when ACLs are in place to block TCP traffic

 

Correct Answer: A

Explanation:

Mixing TCP with UDP

It is a general best practice to not mix TCP-based traffic with UDP-based traffic (especially Streaming-Video) within a single service-provider class because of the behaviors of these protocols during periods of congestion. Specifically, TCP transmitters throttle back flows when drops are detected. Although some UDP applications have application-level windowing, flow control, and retransmission capabilities, most UDP transmitters are completely oblivious to drops and, thus, never lower transmission rates because of dropping. When TCP flows are combined with UDP flows within a single service-provider class and the class experiences congestion, TCP flows continually lower their transmission rates, potentially giving up their bandwidth to UDP flows that are oblivious to drops. This effect is called TCP starvation/UDP dominance.

TCP starvation/UDP dominance likely occurs if (TCP-based) Mission-Critical Data is assigned to the same service-provider class as (UDP-based) Streaming-Video and the class experiences sustained congestion. Even if WRED is enabled on the service-provider class, the same behavior would be observed because WRED (for the most part) manages congestion only on TCP-based flows.

Reference:

http://www.cisco.com/c/en/us/td/docs/solutions/Enterprise/WAN_and_MAN/QoS_SRND/QoS-SRND-Book/VPNQoS.html

 

 

QUESTION 13

Prior to enabling PPPoE in a virtual private dialup network group, which task must be completed?

 

A.

Disable CDP on the interface.

B.

Execute the vpdn enable command.

C.

Execute the no switchport command.

D.

Enable QoS FIFO for PPPoE support.

 

Correct Answer: B

Explanation:

Enabling PPPoE in a VPDN Group

Perform this task to enable PPPoE in a virtual private dial-up network (VPDN) group.

Restrictions

This task applies only to releases prior to Cisco IOS Release 12.2(13)T.

SUMMARY STEPS

clip_image002

1. enable

2. configure terminal

3. vpdn enable

4. vpdn-group name

5. request-dialin

6. protocol pppoe

 

DETAILED STEPS

Command or Action

Step 1

enable

Example:

Router> enable

Enables privileged EXEC mode.

Enter your password if prompted.

Step 2

configure terminal

Example:

Router# configure terminal

Enters global configuration mode.

Step 3

vpdn enable

Example:

Router(config)# vpdn enable

Enables virtual private dialup networking.

Step 4

vpdn-group name

Example:

Router(config)# vpdn-group group1

Associates a VPDN group with a customer or VPDN profile.

Step 5

request-dialin

Example:

Router(config-vpdn)# request-dialin

Creates a request-dialin VPDN subgroup.

Step 6

protocol pppoe

Example:

Router(config-vpdn-req-in)# protocol pppoe

Enables the VPDN subgroup to establish PPPoE

 

Reference:

http://www.cisco.com/en/US/docs/ios/12_2t/12_2t2/feature/guide/ftpppoec_support_TSD_Island_o f_Content_Chapter.html

 

 

 

 

 

QUESTION 14

A network engineer has been asked to ensure that the PPPoE connection is established and authenticated using an encrypted password. Which technology, in combination with PPPoE, can be used for authentication in this manner?

 

A.

PAP

B.

dot1x

C.

IPsec

D.

CHAP

E.

ESP

 

Correct Answer: D

Explanation:

With PPPoE, the two authentication options are PAP and CHAP. When CHAP is enabled on an interface and a remote device attempts to connect to it, the access server sends a CHAP packet to the remote device. The CHAP packet requests or “challenges” the remote device to respond. The challenge packet consists of an ID, a random number, and the host name of the local router. When the remote device receives the challenge packet, it concatenates the ID, the remote device’s password, and the random number, and then encrypts all of it using the remote device’s password. The remote device sends the results back to the access server, along with the name associated with the password used in the encryption process. When the access server receives the response, it uses the name it received to retrieve a password stored in its user database. The retrieved password should be the same password the remote device used in its encryption process. The access server then encrypts the concatenated information with the newly retrieved password–if the result matches the result sent in the response packet, authentication succeeds.

The benefit of using CHAP authentication is that the remote device’s password is never transmitted in clear text (encrypted). This prevents other devices from stealing it and gaining illegal access to the ISP’s network.

Reference:

http://www.cisco.com/c/en/us/td/docs/ios/12_2/security/configuration/guide/fsecur_c/scfathen.html

 

 

QUESTION 15

A corporate policy requires PPPoE to be enabled and to maintain a connection with the ISP, even if no interesting traffic exists. Which feature can be used to accomplish this task?

 

A.

TCP Adjust

B.

Dialer Persistent

C.

PPPoE Groups

D.

half-bridging

E.

Peer Neighbor Route

 

Correct Answer: B

Explanation:

A new interface configuration command, dialer persistent, allows a dial-on-demand routing (DDR) dialer profile connection to be brought up without being triggered by interesting traffic. When configured, the dialer persistent command starts a timer when the dialer interface starts up and starts the connection when the timer expires. If interesting traffic arrives before the timer expires, the connection is still brought up and set as persistent. The command provides a default timer interval, or you can set a custom timer interval. To configure a dialer interface as persistent, use the following commands beginning in global configuration mode:

 

Command

Purpose

Step 1

Router(config)# interface dialer number

Creates a dialer interface and enters interface configuration mode.

Step 2

Router(config-if)# ip address address mask

Specifies the IP address and mask of the dialer interface as a node in the destination network to be called.

Step 3

Router(config-if)# encapsulation type

Specifies the encapsulation type.

Step 4

Router(config-if)# dialer string dial-string class class-name

Specifies the remote destination to call and the map class that defines characteristics for calls to this destination.

Step 5

Router(config-if)# dialer pool number

Specifies the dialing pool to use for calls to this destination.

Step 6

Router(config-if)# dialer-group group-number

Assigns the dialer interface to a dialer group.

Step 7

Router(config-if)# dialer-list dialer-group protocol protocol-name {permit | deny | list access-list- number}

Specifies an access list by list number or by protocol and list number to define the interesting packets that can trigger a call.

Step 8

Router(config-if)# dialer remote-name user-name

(Optional) Specifies the authentication name of the remote router on the destination subnetwork for a dialer interface.

Step 9

Router(config-if)# dialer persistent [delay [initial] seconds | max-attempts number]

Forces a dialer interface to be connected at all times, even in the absence of interesting traffic.

 

Reference:

http://www.cisco.com/c/en/us/td/docs/ios/dial/configuration/guide/12_4t/dia_12_4t_book/dia_dialer _persist.html

 

 

QUESTION 16

Which PPP authentication method sends authentication information in cleartext?

 

A.

MS CHAP

B.

CDPCP

C.

CHAP

D.

PAP

 

Correct Answer: D

Explanation:

PAP authentication involves a two-way handshake where the username and password are sent across the link in clear text; hence, PAP authentication does not provide any protection against playback and line sniffing.

CHAP authentication, on the other hand, periodically verifies the identity of the remote node using a three-way handshake. After the PPP link is established, the host sends a “challenge” message to the remote node. The remote node responds with a value calculated using a one-way hash function. The host checks the response against its own calculation of the expected hash value. If the values match, the authentication is acknowledged; otherwise, the connection is terminated.

Reference:

http://www.cisco.com/c/en/us/support/docs/wan/point-to-point-protocol-ppp/10241-ppp-callin-hostname.html

 

 

QUESTION 17

Which protocol uses dynamic address mapping to request the next-hop protocol address for a specific connection?

 

A.

Frame Relay inverse ARP

B.

static DLCI mapping

C.

Frame Relay broadcast queue

D.

dynamic DLCI mapping

 

Correct Answer: A

Explanation:

Dynamic address mapping uses Frame Relay Inverse ARP to request the next-hop protocol address for a specific connection, given its known DLCI. Responses to Inverse ARP requests are entered in an address-to-DLCI mapping table on the router or access server; the table is then used to supply the next-hop protocol address or the DLCI for outgoing traffic.

Reference:

http://www.cisco.com/c/en/us/td/docs/ios/12_2/wan/configuration/guide/fwan_c/wcffrely.html

 

 

QUESTION 18

What is the default OSPF hello interval on a Frame Relay point-to-point network?

 

A.

10

B.

20

C.

30

D.

40

 

Correct Answer: A

Explanation:

Before you troubleshoot any OSPF neighbor-related issues on an NBMA network, it is important to remember that an NBMA network can be configured in these modes of operation with the ip ospf network command:

The Hello and Dead Intervals of each mode are described in this table:

Network Type

Hello Interval (secs)

Dead Interval (secs)

Point-to-Point

10

40

Point-to-Multipoint

30

120

Broadcast

10

40

Non-Broadcast

30

120

 

Reference:

http://www.cisco.com/c/en/us/support/docs/ip/open-shortest-path-first-ospf/13693-22.html

 

 

QUESTION 19

PPPoE is composed of which two phases?

 

A.

Active Authentication Phase and PPP Session Phase

B.

Passive Discovery Phase and PPP Session Phase

C.

Active Authorization Phase and PPP Session Phase

D.

Active Discovery Phase and PPP Session Phase

 

Correct Answer: D

Explanation:

PPPoE is composed of two main phases:

Reference:

http://www.cisco.com/c/en/us/td/docs/security/asa/asa92/configuration/vpn/asa-vpn-cli/vpn-pppoe.html

 

 

QUESTION 20

Which statement is true about the PPP Session Phase of PPPoE?

 

A.

PPP options are negotiated and authentication is not performed. Once the link setup is completed, PPPoE functions as a Layer 3 encapsulation method that allows data to be transferred over the PPP link within PPPoE headers.

B.

PPP options are not negotiated and authentication is performed. Once the link setup is completed, PPPoE functions as a Layer 4 encapsulation method that allows data to be transferred over the PPP link within PPPoE headers.

C.

PPP options are automatically enabled and authorization is performed. Once the link setup is completed, PPPoE functions as a Layer 2 encapsulation method that allows data to be encrypted over the PPP link within PPPoE headers.

D.

PPP options are negotiated and authentication is performed. Once the link setup is completed, PPPoE functions as a Layer 2 encapsulation method that allows data to be transferred over the PPP link within PPPoE headers.

 

Correct Answer: D

Explanation:

PPPoE is composed of two main phases:

Reference:

http://www.cisco.com/c/en/us/td/docs/security/asa/asa92/configuration/vpn/asa-vpn-cli/vpn-pppoe.html

 

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