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Q91. What is Nagle's algorithm used for? 

A. To increase the latency 

B. To calculate the best path in distance vector routing protocols 

C. To calculate the best path in link state routing protocols 

D. To resolve issues caused by poorly implemented TCP flow control. 

Answer:

Explanation: 

Silly window syndrome is a problem in computer networking caused by poorly implemented TCP flow control. A serious problem can arise in the sliding window operation when the sending application program creates data slowly, the receiving application program consumes data slowly, or both. If a server with this problem is unable to process all incoming data, it requests that its clients reduce the amount of data they send at a time (the window setting on a TCP packet). If the server continues to be unable to process all incoming data, the window becomes smaller and smaller, sometimes to the point that the data transmitted is smaller than the packet header, making data transmission extremely inefficient. The name of this problem is due to the window size shrinking to a "silly" value. When there is no synchronization between the sender and receiver regarding capacity of the flow of data or the size of the packet, the window syndrome problem is created. When the silly window syndrome is created by the sender, Nagle's algorithm is used. Nagle's solution requires that the sender sends the first segment even if it is a small one, then that it waits until an ACK is received or a maximum sized segment (MSS) is accumulated. 

Reference: http://en.wikipedia.org/wiki/Silly_window_syndrome 


Q92. Which two statements about logging are true? (Choose two.) 

A. Log messages are sent to the console port by default. 

B. Log messages are displayed in a Telnet session by default. 

C. Interface status changes are logged at the Notification level. 

D. Interface status changes are logged at the Informational level. 

E. System restart messages are logged at the Critical level. 

F. Reload requests are logged at the Notification level. 

Answer: A,C 

Explanation: 

By default, switches send the output from system messages and debug privileged EXEC commands to a logging process. The logging process controls the distribution of logging messages to various destinations, such as the logging buffer, terminal lines, or a UNIX syslog server, depending on your configuration. The process also sends messages to the console. 

Table 29-3 Message Logging Level Keywords 

Level Keyword 

Level 

Description 

Syslog Definition 

emergencies 

System unstable 

LOG_EMERG 

alerts 

Immediate action needed 

LOG_ALERT 

critical 

Critical conditions 

LOG_CRIT 

errors 

Error conditions

LOG_ERR 

warnings 

Warning conditions 

LOG_WARNING 

notifications 

Normal but significant condition 

LOG_NOTICE 

informational 

Informational messages only 

LOG_INFO 

debugging 

Debugging messages 

LOG_DEBUG 

The software generates four other categories of messages: 

. Error messages about software or hardware malfunctions, displayed at levels warnings through emergencies. These types of messages mean that the functionality of the switch is affected. For information on how to recover from these malfunctions, see the system message guide for this release. 

. Output from the debug commands, displayed at the debugging level. Debug commands are typically used only by the Technical Assistance Center. 

Interface up or down transitions and system restart messages, displayed at the notifications level. This message is only for information; switch functionality is not affected. 

. Reload requests and low-process stack messages, displayed at the informational level. This message is only for information; switch functionality is not affected. 

References: http://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst2950/software/release/12-

1_9_ea1/configuration/guide/scg/swlog.html

http://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst2960/software/release/12-2_55_se/configuration/guide/scg_2960/swlog.html 


Q93. Refer to the exhibit. 

All of the routers on this network are running RIP. If you edit the R3 RIP process configuration to reduce the number of hops from R3 to R1, which statement about the configuration change is true? 

A. Configuring no passive-interface for GigabitEthernet0/0 in the R3 RIP process reduces the number of hops to R1 by 2. 

B. Configuring no passive-interface for GigabitEthernet0/0 in the R3 RIP process reduces the number of hops to R1 by 1. 

C. Configuring no passive-interface for GigabitEthernet0/1 in the R3 RIP process reduces the number of hops to R1 by 3. 

D. Configuring no passive-interface for GigabitEthernet0/1 in the R3 RIP process reduces the number of hops to R1 by 1. 

Answer:

Explanation: 

By changing the link from R3 to R2 to not be passive, traffic can then take the direct route from R3-R2-R1 instead of the longer path of R3-R6-R5-R4-R1, resulting in two less hops. 


Q94. An NSSA area has two ABRs connected to Area 0. Which statement is true? 

A. Both ABRs translate Type-7 LSAs to Type-5 LSAs. 

B. The ABR with the highest router ID translates Type-7 LSAs to Type-5 LSAs. 

C. Both ABRs forward Type-5 LSAs from the NSSA area to backbone area. 

D. No LSA translation is needed. 

Answer:


Q95. Which statement about the bgp soft-reconfig-backup command is true? 

A. It requires BGP to store all inbound and outbound updates. 

B. It overrides soft reconfiguration for devices that support inbound soft reconfiguration. 

C. When the peer is unable to store updates, the updates are implemented immediately. 

D. It provides soft reconfiguration capabilities for peers that are unable to support route refresh. 

E. It provides outbound soft reconfiguration for peers. 

Answer:


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Q96. What are the minimal configuration steps that are required to configure EIGRP HMAC-SHA2 authentication? 

A. classic router mode, interface XX, authentication mode hmac-sha-256 <password> 

B. named router mode, address-family statement, authentication mode hmac-sha-256 <password> 

C. named router mode, address-family statement, af-interface default, authentication mode hmac-sha-256 <password> 

D. named router mode, address-family statement, authentication mode hmac-sha-256 <password> 

Answer:

Explanation: 

The example below shows how to configure EIGRP HMAC-SHA2 on Cisco router: 

Device(config)# router eigrp name1 

Device(config-router)# address-family ipv4 autonomous-system 45000 

Device(config-router-af)# af-interface ethernet 0/0 

Device(config-router-af-interface)# authentication mode hmac-sha-256 0 password1 

Device(config-router-af-interface)# end 

Reference: http://www.cisco.com/c/en/us/td/docs/ios-xml/ios/iproute_eigrp/configuration/15-sy/ire-15-sy-book/ire-sha-256.html 


Q97. On a network using RIPng, the prefix field of a routing table entry has a value of 0:0:0:0:0:0:0:0. What does this value signify? 

A. The next hop address is unknown. 

B. The next hop address is a site-local address. 

C. The neighboring router has IPv6 ND disabled. 

D. The next hop address must be the originator of the route advertisement. 

E. The associated route follows a default route out of the network. 

Answer:


Q98. Refer to the exhibit. 

Route exchange is failing on a PE edge device configured with this VRF-Lite. Which action can you take to correct the problem? 

A. Configure the vrf-lite capability under the OSPF address families. 

B. Correct the route descriptors. 

C. Correct the OSPF router-ids. 

D. Configure the control plane with a larger memory allocation to allow the device to appear in the routing table. 

Answer:

Explanation: 

Open Shortest Path First version 3 (OSPFv3) operates in nondefault VPN routing and forwarding (VRF) instances for both IPv6 and IPv4 address families and, transports the routes across a Border Gateway Protocol (BGP) or a Multiprotocol Label Switching (MPLS) backbone. On the provider edge (PE) device, customer routes are installed together by OSPFv3 and BGP in a common VRF or address family and each protocol is configured to redistribute the routes of the other. BGP combines the prefixes redistributed into it with a route-distinguisher value defined for the VRF and advertises them to other MPLS-BGP speakers in the same autonomous system using the VPNv4 or VPNv6 address family as appropriate. The OSPFv3 route selection algorithm prefers intra-area routes across the back-door link over inter-area routes through the MPLS backbone. Sham-links are a type of virtual link across the MPLS backbone that connect OSPFv3 instances on different PEs. OSPFv3 instances tunnel protocol packets through the backbone and form adjacencies. Because OSPFv3 considers the sham-link as an intra-area connection, sham-link serves as a valid alternative to an intra-area back-door link. Domain IDs are used to determine whether the routes are internal or external. They describe the administrative domain of the OSPFv3 instance from which the route originates. Every PE has a 48-bit primary domain ID (which may be NULL) and zero or more secondary domain IDs. 

How to Configure VRF-Lite/PE-CE 

. Configuring a VRF in an IPv6 Address Family for OSPFv3 

SUMMARY STEPS 

1. enable 

2. configure terminal 

3. vrf definition vrf-name 

4. rd route-distinguisher 

5. exit 

6. router ospfv3 [process-id] 

7. address-family ipv6 [unicast] [vrf vrf-name] 

8. end 

Reference: http://www.cisco.com/c/en/us/td/docs/ios-xml/ios/iproute_ospf/configuration/15-sy/iro-15-sy-book/iro-vrf-lite-pe-ce.html 


Q99. Refer to the exhibit. 

What kind of load balancing is done on this router? 

A. per-packet load balancing 

B. per-flow load balancing 

C. per-label load balancing 

D. star round-robin load balancing 

Answer:

Explanation: 

Here we can see that for the same traffic source/destination pair of 10.0.0.1 to 14.0.0.2 there were a total of 100 packets (shown by second entry without the *) and that the packets were distributed evenly across the three different outgoing interfaces (34, 33, 33 packets, respectively. 


Q100. What is the preferred method to improve neighbor loss detection in EIGRP? 

A. EIGRP natively detects neighbor down immediately, and no additional feature or configuration is required. 

B. BFD should be used on interfaces that support it for rapid neighbor loss detection. 

C. Fast hellos (subsecond) are preferred for EIGRP, so that it learns rapidly through its own mechanisms. 

D. Fast hellos (one-second hellos) are preferred for EIGRP, so that it learns rapidly through its own mechanisms. 

Answer:

Explanation: 

Bi-directional Forwarding Detection (BFD) provides rapid failure detection times between forwarding engines, while maintaining low overhead. It also provides a single, standardized method of link/device/protocol failure detection at any protocol layer and over any media. 

Reference: “Bidirectional Forwarding Detection for EIGRP” 

http://www.cisco.com/en/US/technologies/tk648/tk365/tk207/technologies_white_paper090 0aecd80243fe7.html