Cisco 642-887 Online Practice Questions and Exam Preparation

Cisco 642-887 Online Questions & Answers

• Question 121:

  Which two characteristics describe the difference between MPLS QoS pipe and short-pipe models? (Choose two)

  A. Short-pipe mode does not need MPLS usage, but pipe mode does.
  B. In short-pipe mode, the egress LSR uses the tunneled PHB marking, but in pipe mode, the egress LSR uses the LSP PHB marking.
  C. Pipe mode does guarantee that the tunneled packet marking remains unchanged, but short-pipe does not.
  D. In short-pipe mode, the egress LSR uses the LSP PHB marking, but in pipe mode, the egress LSR uses the tunneled PHB marking.
  E. Short-pipe mode can be implemented on MPLS networks regardless of the MPLS PHP mechanism usage.
  B. In short-pipe mode, the egress LSR uses the tunneled PHB marking, but in pipe mode, the egress LSR uses the LSP PHB marking.
  E. Short-pipe mode can be implemented on MPLS networks regardless of the MPLS PHP mechanism usage.

• Question 122:

  What are the four fields inside the MPLS shim header? (Choose four.)

  A. EXP
  B. TTL
  C. Version
  D. S
  E. Length
  F. Label
  G. Type
  H. FCS
  A. EXP
  B. TTL
  D. S
  F. Label

• Question 123:

  Which three statements are correct regarding ping mpls command operations? (Choose three.)

  A. MPLS OAM has to be enabled on the router using the mpls oam command.
  B. They use a 127/8 address as the destination address in the MPLS echo request packet.
  C. They use ICMP echo request and ICMP echo reply packets.
  D. They are used to test for a broken LSP.
  E. If there is a broken LSP, instead of using label switching, the packet can still be forwarded based on the destination IP address in the mpls ping echo request packet.
  A. MPLS OAM has to be enabled on the router using the mpls oam command.
  B. They use a 127/8 address as the destination address in the MPLS echo request packet.
  D. They are used to test for a broken LSP.

  ---

  How MPLS Ping works?

  MPLS Ping doesn't rely on ICMP echo messages. Instead it uses UDP protocol with both source and destination port as 3503 and relies on MPLS Echo request and MPLS Echo reply.

  When MPLS ping is triggered from any MPLS router, it will generate UDP segment with source/destination port as 3503. The source address will be selected as usual while the destination address will be 127.0.0.1. The IP TTL will be set to 1.

  Below is a sample IP format when MPLS Ping is originated from R5 to 150.1.6.6/32,

  

  Now the originating LSR will look into the LFIB and populate the label header with respective labels to reach the FEC, in our case 150.1.6.6/32. R4 on receiving the MPLS packet will be able to send to the actual destination only if the LSP is end to end. If the LSP is broken between R4 and R6, R4 will look into the destination IP address which will be 127.0.0.1 and won't be able to perform IP forwarding. As per RFC 1812, a router should not forward any packet that has destination address of 127.0.0.0/8

• Question 124:

  In an IPv6 header, what does a flow label of zero indicate?

  A. The packet is not part of any flow.
  B. The size of the flow label is zero bytes.
  C. The label flow cannot have a value of zero.
  D. The packet belongs to the flow labeled zero.
  A. The packet is not part of any flow.

• Question 125:

  Cisco MPLS TE tunnels recently have been deployed to minimize the utilization of a congested link in the core network. The tunnels are up and the administrative weight is correctly configured, but no improvement has occurred since they went into production. Which IOS command can be used to modify Cisco MPLS TE path selection on an interface?

  A. mpls traffic-eng administrative-weight 100
  B. Is-Is metric 100
  C. ip rsvp bandwidth percent 90
  D. tunnel mpls traffic-eng path-selection metric te
  A. mpls traffic-eng administrative-weight 100

• Question 126:

  Drag each of the QoS mechanisms on the left to match the correct description on the right. (Not all options on the left are used.)

  Select and Place:

  

  

• Question 127:

  An engineer looks at packet captures and sees that the MPLS header field of a packet indicates a bottom of stack field of 0. What can the engineer conclude from this information?

  A. The packet is an AToM packet
  B. One label is on the packet
  C. At least one more MPLS label is on the packet
  D. No labels are on the packet
  C. At least one more MPLS label is on the packet

• Question 128:

  Which QoS technique can be used to protect customer traffic from being dropped by traffic rate limiting performed by the service provider?

  A. LLQ
  B. policing
  C. fair-queue
  D. shaping
  D. shaping

• Question 129:

  An engineer is deploying CB-WRED across the entire core network to enforce the previously deployed CBWFQ and decides to change the WRED default to make it work with DSCP. Which policy-map command enables this new profile on regular Cisco IOS routers?

  A. random-detect
  B. random-detect dscp value
  C. random-detect dscp based
  D. random-detect precedence value
  C. random-detect dscp based

• Question 130:

  Which configuration can a network engineer use to establish high availability for LDP in an MPLS setup?

  A. mpls ldp graceful-restart graceful-restart graceful-restart forwarding state-holdtime 180 graceful-restart reconnect-timeout 15 interface HundredGigE0/4/0/0
  B. mpls ldp graceful-restart graceful-restart forwarding state-holdtime 180 graceful-restart reconnect-timeout 15
  C. mpls ldp session protection for peer_acl duration 60 ipv4 access-list peer_acl 10 permit ip host 192.168.10.1 any
  D. router ospf 1 mpls ldp sync mpls ldp igp sync delay 30
  E. mpls ldp router-id loopback0 discovery hello holdtime 15 discovery hello interval 5
  A. mpls ldp graceful-restart graceful-restart graceful-restart forwarding state-holdtime 180 graceful-restart reconnect-timeout 15 interface HundredGigE0/4/0/0