642-780 Maintaining Cisco Service Provider VPNs and MPLS Networks (MSPVM)

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Question 1

Directed LDP sessions are used by MPLS to exchange labels with nonadjacent routers.
How are directed LDP sessions different from normal LDP sessions?

  • A. The hello packets are addressed with a statically configured destination address.
  • B. The ":0" LDP identifier is added to the destination IP address to indicate the label space.
  • C. Directed LDP hello messages are sent to the multicast address 224.0.0.2.
  • D. TCP and UDP well-known port 646 is used for directed LDP sessions only.


Answer : A

Explanation: Explanation/Reference: The only difference between directly and non-directly connected neighbors is in how they discover each other. LSRs discover directly connected neighbors by sending LDP hello messages encapsulated in UDP to the 224.0.0.2 multicast address (all routers on a subnet). These packets are known as hello messages. Non-directly connected neighbors can't be reached through a multicast UDP packet. So, the same hello messages are sent as unicasts (also to UDP port 646). This requires that an LSR know ahead of time who it wants to have as a non-directly connected neighbor. This can be achieved through configuration. Directly connected neighbors- These neighbors have a Layer 2 connection between them. So, routers that are connected by any Layer 2 link-whether a POS link, an ATM PVC, an Ethernet connection, or a DS-3 interface-are considered directly connected for LDP. Neighbors connected by a logical connection such as GRE tunnel are also considered directly connected. The basic commonality over such connections is the fact that a neighbor is one IP hop away. Non-directly connected neighbors- These neighbors do not have a Layer 2 connection between them. More importantly, these neighbors are several IP hops away. Routers that are connected to each other by MPLS traffic engineering tunnels and that have LDP enabled on them are considered non-directly connected. Such an LDP session is called a targeted or directed LDP session

Question 2

Refer to the exhibit.


A layer 3 VPN is configured between PE1 and PE2. CE1 is connected to PE1. CE2 is
connected to PE2. CE1 and CE2 are in VRF red. From which router does the prefix
10.170.170.0/24 originates?

  • A. CE1
  • B. PE1
  • C. PE2
  • D. CE2


Answer : A

Question 3

Refer to the exhibit.


What type of MPLS LAYER 3 VPN configurations is represented?

  • A. Simple two-VPN scenario
  • B. Overlapping VPNs
  • C. Central services VPNs
  • D. Extranet VPNs


Answer : C

Explanation: Explanation/Reference:

Question 4

Which decode corresponds correctly to this MPLS header. 0x00 0x04 0xAB 0xFE?

  • A. Label: 0004, Exp AB. S:1.TTL:7E
  • B. Label: 0004A. TTL:BF.Exp:8. S:0
  • C. Label: 0004A , Exp: 5, S: 1, TTL: FE
  • D. Label: 0004. TTL:AB.Exp:7E.S:1


Answer : C

Explanation: Explanation/Reference:

Question 5

Which command is most likely to be useful when you troubleshoot a unidirectional
connectivity problem on a VC?

  • A. show mpls l2transport vc
  • B. show mpls l2transport vc detail
  • C. show mpls l2transport checkpoint
  • D. show mpls l2transport summary


Answer : B

Explanation: Explanation/Reference:

Question 6

Refer to the exhibit.


The commands in the figure were executed from a cisco ASR 9000 series router. The
remote end of the ping is a cisco XR12000 series router. Which statement is true?

  • A. The XR 12000 has an access list that blacks the MPLS pseudowire ping
  • B. The interface connected to the XR 12000 is not running LDP
  • C. These results will occur during convergence when MPLS LDP sync is enabled
  • D. The MPLS pseudowire ping was not sent


Answer : D

Explanation: Explanation Explanation/Reference: http://www.cisco.com/en/US/docs/ios/12_4t/12_4t11/ht_lspng.html

Question 7

You have implemented MPLS-TE on the core and enabled Fast Reroute. BFD is
configured on the core facing links.
Every thing was working normally until last month when you added video service on the
network. Because of business requirements, video packets are treated as high priority and
70% of bandwidth is allocated for the low latency queue.
Recently you noticed BFD session losses and MPLS-TE tunnel flaps on the network.
Which parameter should you have mentioned proactively to avoid this issue?

  • A. BFD session timers and hello message
  • B. MPLS-TE tunnel bandwidth and utilization
  • C. QoS drops for each class of service on core-facing links
  • D. CPU utilization on the PE routers
  • E. Latency and jitter between PE routers


Answer : A

Question 8

You have been asked to verify if the OSPF protocol is enabled for Layer 3 MPLS VPN
service on the link between the PE and CE.
Assume the PE is running on Cisco IOS XR software. Which command should be used to
verify that the OSPF protocol is enabled for Layer 3 MPLS VPN service on a link between a
PE router and a CE router?

  • A. show ip ospf interface brief
  • B. show vrf VRFNAME detail
  • C. show ospf vrf VRFNAME interface brief
  • D. show ospf interface brief
  • E. show ip protocols


Answer : C

Explanation: Explanation/Reference:

Question 9


Refer to the exhibit. What could cause the pseudowire for bridge group GROUP5 to be
down?

  • A. An interface along the LSP is not running LDP
  • B. The PW type needs to be changed to be VLAN mode
  • C. The MTU needs to be increased by four to include the VLAN header
  • D. The local and remote labels do not match


Answer : D

Question 10

Refer to the exhibit.


The command was executed on a Cisco XR12000 series router. Which statement about
the tunnel displayed is true?

  • A. The command was executed on the head end of the tunnel
  • B. A label of 16003 will be used to reach the next hop for the tunnel
  • C. 10.200.200.0 is the IP address of remote interface of the next downstream hop for the tunnel.
  • D. The command was executed on the tail end of the tunnel


Answer : D

Question 11

Refer to the exhibit.


Which statement about the two show commands output is true?

  • A. The CE-PE routing protocol between the PE and the Customer_1 CE router is BGP.
  • B. The PE router has learned four prefixes over the multiprotocol BGP session.
  • C. 192.168.1.33 is the CE router and 150.1.11.17 is the PE router.
  • D. The PE router is supporting more than one MPLS Layer 3 VPN customers.


Answer : B

Question 12

Refer to the exhibit.


The commands were exceeded on a cisco XR12000 PE. Which statement is true?

  • A. The outer label for prefix 10.22.22.22 is 143989.
  • B. The outer label for prefix 10.22.22.22 is 16000.
  • C. The outer label for prefix 10.22.22.22 is implNull.
  • D. Prefix 10.22.22.22 has no outer label.


Answer : A

Explanation: The outer label for prefix 10.22.22.22 is 143989.

Question 13

What are four essential parts of the MP-BGP VPNv4 update? (Choose four)

  • A. LDP label
  • B. VPN label
  • C. IPv4 prefix with route descriptor
  • D. LSP identifier
  • E. BGP next-hop address
  • F. Route targets (extended communities)


Answer : B,C,E,F

Question 14

Your company has decided to deploy a MPLS network with VPNs. The customer that will
be using the network is demanding service level agreements with your company. What
OSS system should violations be sent to?

  • A. RMON
  • B. event management system
  • C. asset management system
  • D. CNR
  • E. IP SLA


Answer : B

Question 15

Customer A is experiencing intermittent network performance problems. The SP NOC has
determined that the MPLS blackhole is occurring during network convergence events.
The suspected cause of the MPLS VPN traffic issue is that the customers IGP (OSPF) is
converging faster than the LDP. What MPLS feature can be configured to eliminate the
problem?

  • A. Decrease the OSPF convergence timing (throttle timer)
  • B. MPLS VRF protection feature
  • C. MPLS fast reroute feature
  • D. MPLS LDP Sync feature in OSPF
  • E. Use Cisco MPLS Auto bandwidth Allocator


Answer : D

Explanation: Explanation/Reference: Packet loss can occur because the actions of the IGP and LDP are not synchronized. Packet loss can occur in the following situations: When an IGP adjacency is established, the router begins forwarding packets using the new adjacency before the LDP label exchange completes between the peers on that link. If an LDP session closes, the router continues to forward traffic using the link associated with the LDP peer rather than an alternate pathway with a fully synchronized LDP session. The MPLS LDP-IGP Synchronization feature: Provides a means to synchronize LDP and IGPs to minimize MPLS packet loss. Enables you to globally enable LDP-IGP Synchronization on each interface associated with an IGP Open Shortest Path First (OSPF) or IS-IS process. Provides a means to disable LDP-IGP Synchronization on interfaces that you do not want enabled. Prevents MPLS packet loss due to synchronization conflicts. Works when LDP is enabled on interfaces using either the mpls ip or mpls ldp autoconfig command. To enable LDP-IGP Synchronization on each interface that belongs to an OSPF or IS-IS process, enter the mpls ldp sync command. If you do not want some of the interfaces to have LDP-IGP Synchronization enabled, issue the no mpls ldp igp sync command on those interfaces. If the LDP peer is reachable, the IGP waits indefinitely (by default) for synchronization to be achieved. To limit the length of time the IGP session must wait, enter the mpls ldp igp sync holddown command. If the LDP peer is not reachable, the IGP establishes the adjacency to enable the LDP session to be established. When an IGP adjacency is established on a link but LDP-IGP Synchronization is not yet achieved or is lost, the IGP advertises the max-metric on that link

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