Cisco 351-001 Online Practice Questions and Exam Preparation

Cisco 351-001 Online Questions & Answers

• Question 521:

  Refer to the exhibit.

  

  Which statement is true?

  A. The "+" indicates that the routes will be removed after a times expires.
  B. The "+" indicates that the routes were added through multicast static route.
  C. The "+" indicates that the routes are replicated routes from the unicast RIB.
  D. The "+" indicates that the routes are SAFI 2 routes.
  C. The "+" indicates that the routes are replicated routes from the unicast RIB.

• Question 522:

  Which two mechanisms can be used to eliminate Cisco Express Forwarding polarization? (Choose two.)

  A. alternating cost links
  B. the unique-ID/universal-ID algorithm
  C. Cisco Express Forwarding antipolarization
  D. different hashing inputs at each layer of the network
  B. the unique-ID/universal-ID algorithm
  D. different hashing inputs at each layer of the network

  ---

  This document describes how Cisco Express Forwarding (CEF) polarization can cause suboptimal use of redundant paths to a destination network. CEF polarization is the effect when a hash algorithm chooses a particular path and the redundant paths remain completely unused. How to Avoid CEF Polarization Alternate between default (SIP and DIP) and full (SIP + DIP + Layer4 ports) hashing inputs configuration at each layer of the network. Alternate between an even and odd number of ECMP links at each layer of the network.The CEF load-balancing does not depend on how the protocol routes are inserted in the routing table. Therefore, the OSPF routes exhibit the same behavior as EIGRP. In a hierarchical network where there are several routers that perform load-sharing in a row, they all use same algorithm to load-share.

  The hash algorithm load-balances this way by default:

  1: 1

  2: 7-8

  3: 1-1-1

  4: 1-1-1-2

  5: 1-1-1-1-1

  6: 1-2-2-2-2-2

  7: 1-1-1-1-1-1-1

  8: 1-1-1-2-2-2-2-2

  The number before the colon represents the number of equal-cost paths. The number after the colon represents the proportion of traffic which is forwarded per path.

  This means that:

  For two equal cost paths, load-sharing is 46.666%-53.333%, not 50%-50%. For three equal cost paths, load-sharing is 33.33%-33.33%-33.33% (as expected). For four equal cost paths, load-sharing is 20%-20%-20%-40% and not 25%-25%25%-25%. This illustrates that, when there is even number of ECMP links, the traffic is not load- balanced. Cisco IOS introduced a concept called unique-ID/universal-ID which helps avoid CEF polarization. This algorithm, called the universal algorithm (the default in current Cisco IOS versions), adds a 32-bit router-specific value to the hash function (called the universal ID - this is a randomly generated value at the time of the switch boot up that can can be manually controlled). This seeds the hash function on each router with a unique ID, which ensures that the same source/destination pair hash into a different value on different routers along the path. This process provides a better network-wide load-sharing and circumvents the polarization issue. This unique -ID concept does not work for an even number of equal-cost paths due to a hardware limitation, but it works perfectly for an odd number of equal-cost paths. In order to overcome this problem, Cisco IOS adds one link to the hardware adjacency table when there is an even number of equal- cost paths in order to make the system believe that there is an odd number of equal-cost links.

  Reference: http://www.cisco.com/c/en/us/support/docs/ip/express-forwarding-cef/116376- technote-cef-00.html

• Question 523:

  Which topology allows the split-horizon rule to be safely disabled when using EIGRP?

  A. full mesh
  B. partial mesh
  C. hub and spoke
  D. ring
  C. hub and spoke

• Question 524:

  Refer to the exhibit.

  

  Which two statements can this output verify? (Choose two)

  A. The device will wait 200 ms before retransmitting an EIGRP packet.
  B. The device must receive an EIGRP packet within 24 seconds to maintain a neighbor relationship.
  C. The EIGRP neighbor has been up for 28 seconds.
  D. The device must receive an EIGRP packet within 28 seconds to maintain a neighbor relationship.
  E. The device will tear down and restart its EIGRP process in 24 seconds.
  F. The EIGRP neighbor has been up for 28 ms.
  A. The device will wait 200 ms before retransmitting an EIGRP packet.
  C. The EIGRP neighbor has been up for 28 seconds.

• Question 525:

  Which two options are BGP attributes that are updated when router sends an update to its eBGP peer? (Choose two.)

  A. weight
  B. local preference
  C. AS_path
  D. next-hop
  C. AS_path
  D. next-hop

  ---

  AS_Path describes the inter-AS path taken to reach a destination. It gives a list of AS Numbers traversed when reaching to a destination. Every BGP speaker when advertising a route to a peer will include its own AS number in the NLRI. The subsequent BGP speakers who advertise this route will add their own AS number to the AS_Path, the subsequent AS numbers get prepended to the list. The end result is the AS_Path attribute is able to describe all the autonomous systems it has traversed, beginning with the most recent AS and ending with the originating AS. NEXT_HOP Attribute specifies the next hop IP address to reach the destination advertised in the NLRI. NEXT_HOP is a well-known mandatory attribute that is included in every eBGP update.

  Reference: http://netcerts.net/bgp-path-attributes-and-the-decision-process/

• Question 526:

  DRAG DROP

  Drag and drop each GET VPN feature on the left to the corresponding function it performs on the right.

  Select and Place:

  

  

• Question 527:

  What can PfR passive monitoring mode measure for TCP flows?

  A. only delay
  B. delay and packet loss
  C. delay and reachability
  D. delay, packet loss, and throughput
  E. delay, packet loss, throughput, and reachability
  E. delay, packet loss, throughput, and reachability

  ---

  Passive monitoring metrics include the following:

  ?Delay: Cisco PfR measures the average delay of TCP flows for a given prefix or traffic class. Delay is the measurement of the round-trip response time (RTT) between the transmission of a TCP synchronization message and receipt of the

  TCP acknowledgement. ?Packet loss: Cisco PfR measures packet loss by tracking TCP sequence numbers for each TCP flow; it tracks the highest TCP sequence number. If it receives a subsequent packet with a lower sequence number,

  PfR increments the packet-loss counter. Packet loss is measured in packets per million. ?Reachability: Cisco PfR measures reachability by tracking TCP synchronization messages that have been sent repeatedly without receiving a TCP

  acknowledgement. ?Throughput: Cisco PfR measures TCP throughput by measuring the total number of bytes and packets for each interesting traffic class or prefix for a given interval of time.

  Reference: http://www.cisco.com/c/en/us/products/collateral/ios-nx-os- software/performance-routing-pfr/product_data_sheet0900aecd806c4ee4.html

• Question 528:

  Which two statements about the function of a PIM designated router are true? (Choose two.)

  A. It forwards multicast traffic from the source into the PIM network.
  B. It registers directly connected sources to the PIM rendezvous point.
  C. It sends PIM Join/Prune messages for directly connected receivers.
  D. It sends IGMP queries.
  E. It sends PIM asserts on the interfaces of the outgoing interface list.
  B. It registers directly connected sources to the PIM rendezvous point.
  C. It sends PIM Join/Prune messages for directly connected receivers.

  ---

  In PIM ASM and SSM modes, the software chooses a designated router (DR) from the routers on each network segment. The DR is responsible for forwarding multicast data for specified groups and sources on that segment.

  In ASM mode, the DR is responsible for unicasting PIM register packets to the RP. When a DR receives an IGMP membership report from a directly connected receiver, the shortest path is formed to the RP, which may or may not go through

  the DR. The result is a shared tree that connects all sources transmitting on the same multicast group to all receivers of that group.

  In SSM mode, the DR triggers (*, G) or (S, G) PIM join messages toward the RP or the source. The path from the receiver to the source is determined hop by hop.

  The source must be known to the receiver or the DR.

  Reference: http://www.cisco.com/c/en/us/td/docs/switches/datacenter/sw/5_x/nx- os/multicast/configuration/guide/n7k_multic_cli_5x/pim.html#wp1054047

• Question 529:

  Refer to the exhibit.

  

  You are configuring the S1 switch for the switch port that connects to the client computer. Which configuration blocks users on the port from using more than 6 Mbps of traffic and marks the traffic for a class of service of 1?

  E. Exhibit A
  F. Exhibit B
  G. Exhibit C
  H. Exhibit D
  A

  ---

  Only option A specified that the exceed and violate actions are set to drop for traffic over the CIR of 6 Mbps, and is also configured to set all traffic with a COS of 1 using the "set cos1" command.

• Question 530:

  Refer to the exhibit.

  

  You have configured two routing protocols across this point-to-point link. How many BFD sessions will be established across this link?

  A. three per interface
  B. one per multicast address
  C. one per routing protocol
  D. one per interface
  D. one per interface

  ---

  Cisco devices will use one Bidirectional Forwarding Detection (BFD) session for multiple client protocols in the Cisco implementation of BFD for Cisco IOS Releases 12.2(18)SXE, 12.0(31)S, and 12.4(4)T. For example, if a network is running OSPF and EIGRP across the same link to the same peer, only one BFD session will be established, and BFD will share session information with both routing protocols.

  Reference: http://www.cisco.com/c/en/us/td/docs/ios/12_0s/feature/guide/fs_bfd.html#wp1053749