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2017 July Cisco Official New Released 400-101 Q&As
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CCIE Routing and Switching Written Exam v5.1

QUESTION 41

What is the purpose of EIGRP summary leaking?

 

A.

to allow a summary to be advertised conditionally on specific criteria

B.

to allow a component of a summary to be advertised in addition to the summary

C.

to allow overlapping summaries to exist on a single interface

D.

to modify the metric of the summary based on which components of the summary are operational

 

Correct Answer: B

Explanation:

When you do manual summarization, and still you want to advertise some specific routes to the neighbor, you can do
that using leak-map. Please read more about leaking routes here.

http://www.cisco.com/c/en/us/td/docs/ios/iproute_eigrp/command/reference/ire_book/ire_i1.html#w p1037685.

 

 

QUESTION 42

What is the function of an EIGRP sequence TLV packet?

 

A.

to acknowledge a set of sequence numbers during the startup update process

B.

to list the peers that should listen to the next multicast packet during the reliable multicast process

C.

to list the peers that should not listen to the next multicast packet during the reliable multicast process

D.

to define the initial sequence number when bringing up a new peer

 

Correct Answer: C

Explanation:

EIGRP sends updates and other information between routers using multicast packets to 224.0.0.10. For example in the topology below, R1 made a change in the topology and it needs to send updates to R2 & R3. It sends multicast packets to EIGRP multicast address 224.0.0.10. Both R2 & R3 can receive the updates and acknowledge back to R1 using unicast. Simple, right? But what if R1 sends out updates, only R2 replies but R3 never does? In the case a router sends out a multicast packet that must be reliable delivered (like in this case), an EIGRP process will wait until the RTO (retransmission timeout) period has passed before beginning a recovery action. This period is calculated from the SRTT (smooth round-trip time). After R1 sends out updates it will wait for this period to expire. Then it makes a list of all the neighbors from which it did not receive an Acknowledgement (ACK). Next it sends out a packet telling these routers stop listening to multicast until they are been notified that it is safe again. Finally the router will begin sending unicast packets with the information to the routers that didn’t answer, continuing until they are caught up. In our example the process will be like this:

1. R1 sends out updates to 224.0.0.10

2. R2 responds but R3 does not

3. R1 waits for the RTO period to expire

4. R1 then sends out an unreliable-multicast packet, called a sequence TLV (Type-Length-Value) packet, which tells R3 not to listen to multicast packets any more

5. R1 continues sending any other muticast traffic it has and delivering all traffic, using unicast to R3, until it acknowledges all the packets

6. Once R3 has caught up, R1 will send another sequence TLV, telling R3 to begin listening to multicast again.

The sequence TLV packet contains a list of the nodes that should not listen to multicast packets while the recovery takes place. But notice that the TLV packet in step 6 does not contain any nodes in the list.

Note: In the case R3 still does not reply in step 4, R1 will attempt to retransmit the unicast 16 times or continue to retransmit until the hold time for the neighbor in question expires. After this time, R1 will declare a retransmission limit exceeded error and will reset the neighbor. (Reference: EIGRP for IP: Basic Operation and Configuration)

 

 

QUESTION 43

Refer to the exhibit. What does “(received-only)” mean?

 

clip_image001

 

A.

The prefix 10.1.1.1 can not be advertised to any eBGP neighbor.

B.

The prefix 10.1.1.1 can not be advertised to any iBGP neighbor.

C.

BGP soft reconfiguration outbound is applied.

D.

BGP soft reconfiguration inbound is applied.

 

Correct Answer: D

Explanation:

When you configure bgp soft-configuration-inbound, all the updates received from the neighbor will be stored unmodified, regardless of the inbound policy, and these routes appear as “(received-only).”

 

 

 

 

 

 

QUESTION 44

Refer to the exhibit. At which location will the benefit of this configuration be observed?

 

clip_image002

 

A.

on Router A and its upstream routers

B.

on Router A and its downstream routers

C.

on Router A only

D.

on Router A and all of its ARP neighbors

 

Correct Answer: B

Explanation:

The following example shows how to configure the router (and downstream routers) to drop all options packets that enter the network:

Router(config)# ip options drop

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

 

 

QUESTION 45

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

 

clip_image003

 

A.

An mrouter port can be learned by receiving a PIM hello packet from a multicast router.

B.

This switch is configured as a multicast router.

C.

Gi2/0/1 is a trunk link that connects to a multicast router.

D.

An mrouter port is learned when a multicast data stream is received on that port from a multicast router.

E.

This switch is not configured as a multicast router. It is configured only for IGMP snooping.

F.

IGMP reports are received only on Gi2/0/1 and are never transmitted out Gi2/0/1 for VLANs 10 and 20.

 

Correct Answer: ABC

Explanation:

In this example, the switch has been configured as a multicast router since IGMP snooping has been enabled. All mrouters can learn about other mrouters by receiving a PIM hello packet from another multicast router. Also, since two different VLANs are being used by the same port of gi 2/0/1, it must be a trunk link that connects to another multicast router.

 

 

 

 

 

 

 

 

 

QUESTION 46

Refer to the exhibit. Which configuration is missing that would enable SSH access on a router that is running Cisco IOS XE Software?

 

clip_image004

 

A.

int Gig0/0/0

management-interface

B.

class-map ssh-class

match access-group protect-ssh

policy-map control-plane-in

class ssh-class

police 80000 conform transmit exceed drop

control-plane

service-policy input control-plane-in

C.

control-plane host

management-interface GigabitEthernet0/0/0 allow ssh

D.

interface Gig0/0/0

ip access-group protect-ssh in

 

Correct Answer: C

Explanation:

The feature Management Plane Protection (MPP) allows an administrator to restrict on which interfaces management traffic can be received by a device. This allows the administrator additional control over a device and how the device is accessed. This example shows how to enable the MPP in order to only allow SSH and HTTPS on the GigabitEthernet0/1 interface:

!

control-plane host

management-interface GigabitEthernet 0/1 allow ssh https

!

Reference: http://www.cisco.com/c/en/us/support/docs/ip/access-lists/13608-21.html

 

 

QUESTION 47

Two routers are trying to establish an OSPFv3 adjacency over an Ethernet link, but the adjacency is not forming. Which two options are possible reasons that prevent OSPFv3 to form between these two routers? (Choose two.)

 

A.

mismatch of subnet masks

B.

mismatch of network types

C.

mismatch of authentication types

D.

mismatch of instance IDs

E.

mismatch of area types

 

Correct Answer: DE

Explanation:

An OSPFv3 interface must have a compatible configuration with a remote interface before the two can be considered neighbors. The two OSPFv3 interfaces must match the following criteria:

 

clip_image006Hello interval

clip_image006[1]Dead interval

clip_image006[2]Area ID

clip_image006[3]Optional capabilities

 

The OSPFv3 header includes an instance ID field to identify that OSPFv3 packet for a particular OSPFv3 instance. You can assign the OSPFv3 instance. The interface drops all OSPFv3 packets that do not have a matching OSPFv3 instance ID in the packet header.

 

Reference: http://www.cisco.com/c/en/us/td/docs/switches/datacenter/sw/5_x/nx-os/unicast/configuration/guide/l3_cli_nxos/l3_ospfv3.html

 

 

QUESTION 48

Refer to the exhibit. Which statement about this COS-DSCP mapping is true?

 

clip_image007

 

A.

The expedited forwarding DSCP is mapped to COS 3..

B.

COS 16 is mapped to DSCP 2.

C.

The default COS is mapped to DSCP 32.

D.

This mapping is the default COS-DSCP mapping on Cisco switches.

 

Correct Answer: A

Explanation:

Here we see that COS 3 is mapped to DSCP 46, which is the Expedited forwarding class:

The Expedited Forwarding (EF) model is used to provide resources to latency (delay) sensitive real-time, interactive traffic. The EF model uses one marking — DSCP 46.

 

 

QUESTION 49

Which statement is true about VPLS?

 

A.

MPLS is not required for VPLS to work.

B.

VPLS carries packets as Layer 3 multicast.

C.

VPLS has been introduced to address some shortcomings of OTV.

D.

VPLS requires an MPLS network.

 

Correct Answer: D

Explanation:

VPLS uses MPLS labels so an MPLS network is required. VPLS MPLS packets have a two-label stack. The outer label is used for normal MPLS forwarding in the service provider’s network. If BGP is used to establish the VPLS, the inner label is allocated by a PE as part of a label block. If LDP is used, the inner label is a virtual circuit ID assigned by LDP when it first established a mesh between the participating PEs. Every PE keeps track of assigned inner label, and associates these with the VPLS instance.

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

 

 

QUESTION 50

Refer to the exhibit. While troubleshooting high CPU utilization on one of your Cisco Catalyst switches, you find that the issue is due to excessive flooding that is caused by STP. What can you do to prevent this issue from happening again?

 

clip_image009

 

A.

Disable STP completely on the switch.

B.

Change the STP version to RSTP.

C.

Configure PortFast on port-channel 1.

D.

Configure UplinkFast on the switch.

E.

Configure PortFast on interface Gi0/15.

 

Correct Answer: E

Explanation:

Topology Changes (TC) should be a rare event in a well-configured network. When a link on a switch port goes up or down, there is eventually a TC, once the STP state of the port is changing to or from forwarding. When the port is flapping, this would cause repetitive TCs and flooding. Ports with the STP portfast feature enabled will not cause TCs when going to or from the forwarding state. The configuration of portfast on all end-device ports (such as printers, PCs, and servers) should limit TCs to a low amount and is highly recommended.

Reference: http://www.cisco.com/c/en/us/support/docs/lan-switching/spanning-tree-protocol/28943-170.html

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