Ensurepass

CCIE Routing and Switching Written Exam v5.1

 

QUESTION 71

Refer to the exhibit. ICMP Echo requests from host A are not reaching the intended destination on host B. What is the problem?

 

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A.

The ICMP payload is malformed.

B.

The ICMP Identifier (BE) is invalid.

C.

The negotiation of the connection failed.

D.

The packet is dropped at the next hop.

E.

The link is congested.

 

Correct Answer: D

Explanation:

Here we see that the Time to Live (TTL) value of the packet is one, so it will be forwarded to the next hop router, but then dropped because the TTL value will be 0 at the next hop.

 

 

 

 

 

 

QUESTION 72

Refer to the exhibit. Which statement about this device configuration is true?

 

clip_image004

 

A.

The NMS needs a specific route configured to enable it to reach the Loopback0 interface of the device.

B.

The ifindex of the device could be different when the device is reloaded.

C.

The device will allow anyone to poll it via the public community.

D.

The device configuration requires the AuthNoPriv security level.

 

Correct Answer: B

Explanation:

One of the most commonly used identifiers in SNMP-based network management applications is the Interface Index (ifIndex) value. IfIndex is a unique identifying number associated with a physical or logical interface. For most software, the ifIndex is the name of the interface. Although relevant RFCs do not require that the correspondence between particular ifIndex values and their interfaces be maintained across reboots, applications such as device inventory, billing, and fault detection depend on this correspondence.

Consider a situation where a simple monitoring software (like MRTG) is polling the interface statistics of the router specific serial interface going to the internet.

As an example, you could have these conditions prior to re-initialization:

physical port

ifIndex

ethernet port

1

tokenring port

2

serial port

3

Therefore, the management application is polling the ifIndex 3, which corresponds to the serial port.

After the router re-initialization (reboot, reload and so on) the conditions change to something similar to this:

physical port

ifIndex

ethernet port

3

tokenring port

1

serial port

2

The management application continues polling the ifIndex 3, which corresponds now to the ethernet port. Therefore, if the management application is not warned by a trap, for example, that the router has been rebooted, the statistics polled could be completely wrong.

Reference: http://www.cisco.com/c/en/us/support/docs/ip/simple-network-management-protocol-snmp/28420-ifIndex-Persistence.html

 

 

QUESTION 73

Refer to the exhibit. Which statement is true about a VPNv4 prefix that is present in the routing table of vrf one and is advertised from this router?

 

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A.

The prefix is advertised only with route target 100:1.

B.

The prefix is advertised with route targets 100:1 and 100:2.

C.

The prefix is advertised only with route target 100:3.

D.

The prefix is not advertised.

E.

The prefix is advertised with route targets 100:1, 100:2, and 100:3.

 

Correct Answer: A

Explanation:

The route target used for prefix advertisements to other routers is defined on the route-target export command, which shows 100:1 in this case for VPNv4 routes.

 

 

QUESTION 74

Which statement is true comparing L2TPv3 to EoMPLS?

 

A.

L2TPv3 requires OSPF routing, whereas EoMPLS does not.

B.

EoMPLS requires BGP routing, whereas L2TPv3 does not.

C.

L2TPv3 carries L2 frames inside MPLS tagged packets, whereas EoMPLS carries L2 frames inside IPv4 packets.

D.

L2TPv3 carries L2 frames inside IPv4 packets, whereas EoMPLS carries L2 frames inside MPLS packets.

 

Correct Answer: D

Explanation:

Ethernet-over-MPLS (EoMPLS) provides a tunneling mechanism for Ethernet traffic through an MPLS-enabled L3 core and encapsulates Ethernet protocol data units (PDUs) inside MPLS packets (using label stacking) to forward them across the MPLS network. Another technology that more or less achieves the result of AToM is L2TPV3. In the case of L2TPV3 Layer 2 frames are encapsulated into an IP packet instead of a labelled MPLS packet.

Reference: http://www.cisco.com/c/en/us/td/docs/routers/asr9000/software/asr9k_r4-3/lxvpn/configuration/guide/lesc43xbook/lesc43p2ps.html

 

 

QUESTION 75

Refer to the exhibit. R3 prefers the path through R1 to reach host 10.1.1.1. Which option describes the reason for this behavior?

 

clip_image008

 

A.

The OSPF reference bandwidth is too small to account for the higher speed links through R2.

B.

The default OSPF cost through R1 is less than the cost through R2.

C.

The default OSPF cost through R1 is more than the cost through R2.

D.

The link between R2 and R1 is congested.

 

Correct Answer: A

Explanation:

The default formula to calculate OSPF bandwidth is BW = Bandwidth Reference / interface bandwidth [bps] = 10^8 / / interface bandwidth [bps]

BW of the R1-R3 link = 10^8 / 100Mbps = 10^8 / 10^8 = 1

BW of the R2-R3 link = 10^8 / 1Gbps = 10^8 / 10^9 = 1 (round up)

Therefore OSPF considers the two above links have the same Bandwidth -> R3 will go to 10.1.1.1 via the R1-R3 link. The solution here is to increase the Bandwidth Reference to a higher value using the “auto-cost reference-bandwidth” command under OSPF router mode. For example:

Router(config)#router ospf 1

Router(config-router)#auto-cost reference-bandwidth 10000

This will increase the reference bandwidth to 10000 Mbps which increases the BW of the R2-R3 link to 10^10 / 10^8 = 100.

 

 

QUESTION 76

Refer to the exhibit. AS #1 and AS #2 have multiple EBGP connections with each other. AS #1 wants all return traffic that is destined to the prefix 10.10.10.1/32 to enter through the router R1 from AS #2. In order to achieve this routing policy, the AS 1 advertises a lower MED from R1, compared to a higher MED from R3, to their respective BGP neighbor for the prefix 10.10.10.0/24. Will this measure guarantee that the routing policy is always in effect?

 

clip_image010

 

A.

Yes, because MED plays a deterministic role in return traffic engineering in BGP.

B.

Yes, because a lower MED forces BGP best-path route selection in AS #2 to choose R1 as the best path for 10.10.10.0/24.

C.

Yes, because a lower MED in AS #2 is the highest BGP attribute in BGP best-path route selection.

D.

No, AS #2 can choose to alter the weight attribute in R2 for BGP neighbor R1, and this weight value is cascaded across AS #2 for BGP best-path route selection.

E.

No, AS #2 can choose to alter the local preference attribute to overwrite the best-path route selection over the lower MED advertisement from AS #1. This local preference attribute is cascaded across AS #2 for the BGP best-path route selection.

 

Correct Answer: E

Explanation:

MED and AS path prepending can both be used to influence the way incoming traffic from other Autonomous Systems get sent to the local AS, but they provide no guarantee as the other AS ultimately has the final word in how they send traffic. Since local preference is preferred over MED in the BGP decision process, the other AS can configure local preference to override the MED settings you have configured.

 

 

 

 

 

QUESTION 77

Refer to the exhibit. Why is the neighbor relationship between R2 and R4 shown as ES-IS?

 

clip_image012

 

A.

because there is an MTU mismatch between R2 and R4

B.

because interface S3/0 of R4 is configured as L1/L2

C.

because interface S3/0 of R2 is configured as L1

D.

because there is a hello interval mismatch between R2 and R4

 

Correct Answer: C

 

 

QUESTION 78

Which two statements are true about an EPL? (Choose two.)

 

A.

It is a point-to-point Ethernet connection between a pair of NNIs.

B.

It allows for service multiplexing.

C.

It has a high degree of transparency.

D.

The EPL service is also referred to as E-line.

 

Correct Answer: CD

Explanation:


Ethernet private line (EPL) and Ethernet virtual private line (EVPL) are carrier Ethernet data services defined by the Metro Ethernet Forum. EPL provides a point-to-point Ethernet virtual connection (EVC) between a pair of dedicated user-network interfaces (UNIs), with a high degree of transparency. EVPL provides a point-to-point or point-to-multipoint connection between a pair of UNIs.

The services are categorized as an E-Line service type, with an expectation of low frame delay, frame delay variation and frame loss ratio. EPL is implemented using a point-to-point (EVC) with no Service Multiplexing at each UNI (physical interface), i.e., all service frames at the UNI are mapped to a single EVC (a.k.a. all-to-one bundling).

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

 

 

 

 

 

 

 

 

QUESTION 79

According to RFC 4577, OSPF for BGP/MPLS IP VPNs, when must the down bit be set?

 

A.

when an OSPF route is distributed from the PE to the CE, for Type 3 LSAs

B.

when an OSPF route is distributed from the PE to the CE, for Type 5 LSAs

C.

when an OSPF route is distributed from the PE to the CE, for Type 3 and Type 5 LSAs

D.

when an OSPF route is distributed from the PE to the CE, for all types of LSAs

 

Correct Answer: C

Explanation:

If an OSPF route is advertised from a PE router into an OSPF area, the Down bit (DN) is set. Another PE router in the same area does not redistribute this route into iBGP of the MPLS VPN network if down is set.

RFC 4577 says:

“When a type 3 LSA is sent from a PE router to a CE router, the DN bit in the LSA Options field MUST be set. This is used to ensure that if any CE router sends this type 3 LSA to a PE router, the PE router will not redistribute it further. When a PE router needs to distribute to a CE router a route that comes from a site outside the latter’s OSPF domain, the PE router presents itself as an ASBR (Autonomous System Border Router), and distributes the route in a type 5 LSA. The DN bit [OSPF-DN] MUST be set in these LSAs to ensure that they will be ignored by any other PE routers that receive them.”

For more information about Down bit according to RFC 4577 please read more here.

http://tools.ietf.org/html/rfc4577#section-4.2.5.1.

 

 

QUESTION 80

Which two DHCP messages are always sent as broadcast? (Choose two.)

 

A.

DHCPOFFER

B.

DHCPDECLINE

C.

DHCPRELEASE

D.

DHCPREQUEST

E.

DHCPDISCOVER

 

Correct Answer: DE

Explanation:

DHCP discovery

The client broadcasts messages DHCPDISCOVER on the network subnet using the destination address 255.255.255.255 or the specific subnet broadcast address.

DHCP request

In response to the DHCP offer, the client replies with a DHCP request, broadcast to the server, requesting the offered address. A client can receive DHCP offers from multiple servers, but it will accept only one DHCP offer.

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

 

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