Ensurepass

CCIE Routing and Switching Written Exam v5.1

 

QUESTION 131

Consider an OSPFv3 network with four parallel links between each pair of routers. Which measure can you use to reduce the CPU load and at the same time keep all links available for ECMP?

 

A.

Configure some interfaces as passive interface.

B.

Configure ipv6 ospf priority 0 on some interfaces.

C.

Configure some routers with a distribute list in ingress of the OSPFv3 process.

D.

Configure ipv6 ospf database-filter all out on some interfaces.

 

Correct Answer: D

Explanation:

To filter outgoing link-state advertisements (LSAs) to an Open Shortest Path First version 3 (OSPFv3) interface, use the ipv6 ospf database-filter all out command in interface configuration mode. This can be done on some of the links to reduce the CPU load while still ensuring that all links in the equal cost path are still being used.

 

 

QUESTION 132

Refer to the exhibit. Which part of the joined group addresses list indicates that the interface has joined the EIGRP multicast group address?

 

clip_image002

 

A.

FF02::1

B.

FF02::1:FF00:200

C.

FF02::A

D.

FF02::2

 

Correct Answer: C

Explanation:

FF02::A is an IPv6 link-local scope multicast addresses. This address is for all devices on a wire that want to “talk” EIGRP with one another.

Focusing specifically on FF02::A and how routers join it, we can see and say three things:

Local: FF02::A is local to the wire.

Join: Each device “joins” FF02::A by just “deciding to listen” to the IPv6 link-local scope multicast address FF02::A. Then, by extension, it listens to the corresponding MAC address for that multicast IPv6 address (33:33:00:00:00:0A).

Common interest: As we can see, these varying groups have something in common that they would all like to hear about. For FF02::A, the common interest — the “connection” among the devices joining that group – is that they all want to listen to or participate in EIGRP.

 

Reference: http://www.networkcomputing.com/networking/understanding-ipv6-what-is-solicited-node-multicast/a/d-id/1315703

 

QUESTION 133

Which variable in an EEM applet is set when you use the sync yes option?

 

A.

$_cli_result

B.

$_result

C.

$_string_result

D.

$_exit_status

 

Correct Answer: D

Explanation:

The CLI event detector screens CLI commands for a regular expression match. When a match is found, an event is published. The match logic is performed on the fully expanded CLI command after the command is successfully parsed and before it is executed. The CLI event detector supports three publish modes:

Synchronous publishing of CLI events–The CLI command is not executed until the EEM policy exits, and the EEM policy can control whether the command is executed. The read/write variable, _exit_status, allows you to set the exit status at policy exit for policies triggered from synchronous events. If _exit_status is 0, the command is skipped, if _exit_status is 1, the command is run.

Asynchronous publishing of CLI events–The CLI event is published, and then the CLI command is executed.

Asynchronous publishing of CLI events with command skipping–The CLI event is published, but the CLI command is not executed.

 

Reference: http://www.cisco.com/c/en/us/td/docs/ios-xml/ios/eem/command/eem-cr-book/eem-cr-e1.html

 

 

QUESTION 134

Refer to the exhibit. Which three statements about the output are true? (Choose three.)

 

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A.

This switch is currently receiving a multicast data stream that is being forwarded out VLAN 150.

B.

A multicast receiver has requested to join one or more of the multicast groups.

C.

Group 224.0.1.40 is a reserved address, and it should not be used for multicast user data transfer.

D.

One or more multicast groups are operating in PIM dense mode.

E.

One or more of the multicast data streams will be forwarded out to neighbor 10.85.20.20 .

F.

Group 239.192.1.1 is a reserved address, and it should not be used for multicast user data transfer.

 

Correct Answer: ABC

Explanation:

A. VLAN 150 shows up in the outgoing interface list so those specific multicast streams are being forwarded to this VLAN.

B. A receiver has requested to receive the multicast stream associated with the multicast address of 239.192.1.1, that is why this stream appears in the mroute table.

C. The 224.0.1.40 is a reserved multicast group for cisco’s Rp descovery. All cisco routers are members of this grup by default and listen to this group for Cisco RP discovery messages advertised by mapping agent even if it is not configured.

 

 

QUESTION 135

Which two statements about port ACLs are true? (Choose two.)

 

A.

Port ACLs are supported on physical interfaces and are configured on a Layer 2 interface on a switch.

B.

Port ACLs support both outbound and inbound traffic filtering.

C.

When it is applied to trunk ports, the port ACL filters only native VLAN traffic.

D.

When it is applied to a port with voice VLAN, the port ACL filters both voice and data VLAN traffic.

 

Correct Answer: AD

Explanation:

PACLs filter incoming traffic on Layer 2 interfaces, using Layer 3 information, Layer 4 header information, or non-IP Layer 2 information The port ACL (PACL) feature provides the ability to perform access control on specific Layer 2 ports. A Layer 2 port is a physical LAN or trunk port that belongs to a VLAN. Port ACLs perform access control on all traffic entering the specified Layer 2 port, including voice and data VLANs that may be configured on the port. Port ACLs are applied only on the ingress traffic.

Reference: http://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst6500/ios/12-2SY/configuration/guide/sy_swcg/port_acls.html

 

 

QUESTION 136

Which two methods change the IP MTU value for an interface? (Choose two.)

 

A.

Configure the default MTU.

B.

Configure the IP system MTU.

C.

Configure the interface MTU.

D.

Configure the interface IP MTU.

 

Correct Answer: CD

Explanation:

An IOS device configured for IP+MPLS routing uses three different Maximum Transmission Unit (MTU) values: The hardware MTU configured with the mtu interface configuration command The hardware MTU specifies the maximum packet length the interface can support … or at least that’s the theory behind it. In reality, longer packets can be sent (assuming the hardware interface chipset doesn’t complain); therefore you can configure MPLS MTU to be larger than the interface MTU and still have a working network. Oversized packets might not be received correctly if the interface uses fixed-length buffers; platforms with scatter/gather architecture (also called particle buffers) usually survive incoming oversized packets.

IP MTU is used to determine whether am IP packet forwarded through an interface has to be fragmented. It has to be lower or equal to hardware MTU (and this limitation is enforced). If it equals the HW MTU, its value does not appear in the running configuration and it tracks the changes in HW MTU. For example, if you configure ip mtu 1300 on a Serial interface, it will appear in the running configuration as long as the hardware MTU is not equal to 1300 (and will not change as the HW MTU changes). However, as soon as the mtu 1300 is configured, the ip mtu 1300 command disappears from the configuration and the IP MTU yet again tracks the HW MTU.

Reference: http://blog.ipspace.net/2007/10/tale-of-three-mtus.html

 

 

QUESTION 137

A service provider is deploying L2VPN LAN services in its MPLS cloud. Which statement is true regarding LDP signaling and autodiscovery?

 

A.

LDP signaling requires that each PE is identified, and that an LDP session is active with its P neighbor for autodiscovery to take place.

B.

LDP signaling requires that each P is identified, and that a targeted LDP session is active for autodiscovery to take place.

C.

LDP signaling requires that each PE is identified, and that a targeted LDP session with a BGP route reflector is active for autodiscovery to take place.

D.

LDP signaling requires that each PE is identified, and that a targeted LDP session is active for autodiscovery to take place.

 

Correct Answer: D

Explanation:

LDP signaling requires that each PE is identified and a targeted LDP session is active for autodiscovery to take place. Although the configuration can be automated using NMS/OSS the overall scalability of the solution is poor as a PE must be associated with all other PEs for LDP discovery to work, which can lead to a large number of targeted LDP sessions (n2), which may be largely unused as not all VPLS will be associated with every PE. The security attributes of LDP are reasonably good, although additional configuration is required to prevent unauthorized sessions being set up. Although LDP can signal additional attributes, it requires additional configuration either from an NMS/OSS or static configuration.

Reference: http://www.cisco.com/en/US/products/hw/routers/ps368/products_white_paper09186a00801f6084.shtml

 

 

QUESTION 138

Which three statements are true about OSPFv3? (Choose three.)

 

A.

The only method to enable OSPFv3 on an interface is via the interface configuration mode.

B.

Multiple instances of OSPFv3 can be enabled on a single link.

C.

There are two methods to enable OSPFv3 on an interface, either via the interface configuration mode or via the router configuration mode.

D.

For OSPFv3 to function, IPv6 unicast routing must be enabled.

E.

For OSPFv3 to function, IPv6 must be enabled on the interface.

F.

Only one instance of OSPFv3 can be enabled on a single link.

Correct Answer: BDE

Explanation:

Here is a list of the differences between OSPFv2 and OSPFv3:

They use different address families (OSPFv2 is for IPv4-only, OSPFv3 can be used for IPv6-only or both protocols (more on this following))

OSPFv3 introduces new LSA types

OSPFv3 has different packet format

OSPFv3 uses different flooding scope bits (U/S2/S1)

OSPFv3 adjacencies are formed over link-local IPv6 communications

OSPFv3 runs per-link rather than per-subnet

OSPFv3 supports multiple instances on a single link, Interfaces can have multiple IPv6 addresses

OSPFv3 uses multicast addresses FF02::5 (all OSPF routers), FF02::6 (all OSPF DRs)

OSPFv3 Neighbor Authentication done with IPsec (AH)

OSPFv2 Router ID (RID) must be manually configured, still a 32-bit number

 

Following is a simple example of OSPFv3 configuration on a Cisco IOS 12.4T router.

 

ipv6 unicast-routing

ipv6 cef

!

interface GigabitEthernet 0/0

description Area 0.0.0.0 backbone interface

ipv6 address 2001:DB8:100:1::1/64

ipv6 ospf network broadcast

ipv6 ospf 100 area 0.0.0.0

 

Reference: http://www.networkworld.com/article/2225270/cisco-subnet/ospfv3-for-ipv4-and-ipv6.html

 

 

QUESTION 139

DRAG DROP

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Correct Answer:

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QUESTION 140

Which switching technology can be used to solve reliability problems in a switched network?

 

A.

fragment-free mode

B.

cut-through mode

C.

check mode

D.

store-and-forward mode

 

Correct Answer: D

Explanation:

Characteristics of Store-and-Forward Ethernet Switching

This section provides an overview of the functions and features of store-and-forward Ethernet switches.

Error Checking

Figure 1 shows a store-and-forward switch receiving an Ethernet frame in its entirety. At the end of that frame, the switch will compare the last field of the datagram against its own frame-check- sequence (FCS) calculations, to help ensure that the packet is free of physical and data-link errors. The switch then performs the forwarding process. Whereas a store-and-forward switch solves reliability issues by dropping invalid packets, cut- through devices forward them because they do not get a chance to evaluate the FCS before transmitting the packet.

Figure 1. Ethernet Frame Entering a Store-and-Forward Bridge or Switch (from Left to Right)

 

clip_image010 

 

Reference: http://
www.cisco.com/c/en/us/products/collateral/switches/nexus-5020-switch/white_paper_c11-465436.html

 

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