Download New Latest (May) Cisco 642-883 Actual Tests 11-20

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QUESTION 11

What are two ways to advertise networks into BGP? (Choose two.)

 

A.

using the neighbor router BGP command

B.

using a route policy in Cisco IOS XR Software or using a route map in Cisco IOS Software or Cisco IOS XE Software

C.

using route redistribution into BGP

D.

using the network router BGP command

E.

enabling an interface to run BGP using the interface router BGP command

 

Answer: CD

 

 

QUESTION 12

Which reserved AS number or range of numbers is used for backward compatibility between old BGP peers using 16-bit AS number and new BGP peers using 32-bit AS number?

 

A.

AS 65001 to 65535

B.

AS 65512 to 65535

C.

AS 12345

D.

AS 23456

E.

AS 64001

 

Answer: D

Explanation:http://www.cisco.com/en/US/prod/collateral/iosswrel/ps6537/ps6554/ps6599/4byte_asnios.

pdf

 

 

 

New Reserved AS#

AS_TRANS = AS #23456

2-byte placeholder for a 4-byte AS number

Used for backward compatibility between OLD and NEW BGP speakers

 

 

QUESTION 13

What are three common problems that can cause a BGP neighbor state to toggle between the idle state and the active state? (Choose three.)

 

A.

BGP network command misconfiguration

B.

route policy misconfiguration

C.

AS number misconfiguration

D.

route map misconfiguration

E.

BGP neighbor peering to wrong IP address

F.

IGP routing problem: not able to reach the source IP address of the BGP open packet

 

Answer: CEF

 

 

QUESTION 14

When configuring Cisco IOS route maps, which command allows the route map processing to jump to another statement instead of exiting?

 

A.

jump

B.

next

C.

set

D.

continue

E.

goto

 

Answer: D

Explanation:Match Operations With Continue Clauses

If a match clause does not exist in the route-map entry but a continue clause does, the continue clause will be automatically executed and go to the specified route-map entry. If a

 

 

 

match clause exists in a route-map entry, the continue clause is executed only when a successful match occurs. When a successful match occurs and a continue clause exists, the route map executes the set clauses and then goes to the specified route-map entry. If the next route map contains a continue clause, the route map will execute the continue clause if a successful match occurs. If a continue clause does not exist in the next route map, the route map will be evaluated normally. If a continue clause exists in the next route map but a match does not occur, the route map will not continue and will “fall through” to the next sequence number if one exists.

 

Set Operations With Continue Clauses

Set clauses are saved during the match clause evaluation process and executed after the route-map evaluation is completed. The set clauses are evaluated and executed in the order in which they were configured. Set clauses are only executed after a successful match occurs, unless the route map does not contain a match clause. The continue statement proceeds to the specified route-map entry only after configured set actions are performed. If a set action occurs in the first route map and then the same set action occurs again, with a different value, in a subsequent route map entry, the last set action may override any previous set actions that were configured with the same set command unless the set command permits more than one value. For example, the set as-path pretend command permits more than one autonomous system number to be configured.

 

 

QUESTION 15

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There are how many IS-IS area(s) defined in this network Scenario?

 

A.

1

B.

2

C.

3

D.

4

 

Answer: C

Explanation: #show clns

 

 

QUESTION 16

Which two statements are true about an EBGP session or an IBGP session? (Choose two.)

 

A.

IBGP uses AS-Path to detect routing information loops within the AS.

B.

EBGP routes have a default Admin Distance of 20 and IBGP routes have a default Admin Distance of 200.

C.

No BGP attributes are changed in EBGP updates except for the next-hop attribute if next-hop-self is configured.

D.

Routes learned from an EBGP peer not advertised to another EBGP peer to prevent routing information loops.

E.

IBGP uses split horizon to prevent routing information loops; routes learned from an IBGP peer are not advertised to another IBGP peer.

 

Answer: BE

 

 

QUESTION 17

What is recursive lookup in BGP and how does it work?

 

A.

The router looks up the EBGP route and the EBGP next hop to reach a destination in the remote AS. Then the router looks up the route to reach the EBGP next hop using the IBGP.

B.

The router looks up the IBGP route and the IBGP next hop to reach a destination in the remote AS. Then the router looks up the route to reach the IBGP next hop using the EBGP.

C.

The router looks up the BGP route and the BGP next hop to reach a destination in the remote AS. Then the router looks up the route to reach the BGP next hop using the IGP.

D.

The router looks up the route and the next hop to reach a destination in the remote AS using the IGP. Then the router looks up the route to reach the next hop using BGP.

E.

The router perform three routing lookups to determine the route to reach a destination in the remote AS. The first lookup is done using EBGP, the second lookup is done using IBGP, and the third lookup is done using the IGP.

 

Answer: C

Explanation:A few different approaches are available to deal with iBGP and synchronization. We may turn on the synchronization option on our routers and wait for the IGP to have a route for the destination before it’s advertised to peers. Another option is to simply use a full mesh, so that iBGP convergence isn’t an issue.

Clearly that isn’t going to happen when a network’s core needs to scale: it will implement something like reflectors that cause iBGP’s full mesh to be broken. The real alternative, if you don’t enable synchronization, is to use route recursion. A recursive route lookup uses the BGP next-hop attribute to actually make a different route lookup. The IGP can use the destination network instead of the AS-path to determine where it gets sent. Even if the iBGP hasn’t converged, the routers will still know how to get to that network, since it will exist in the router it was advertised from, who will know the next-hop.

 

 

QUESTION 18

When implementing OSPF, which type of networks require DR/BDR election?

 

A.

point-to-point networks

B.

mutli-access broadcast networks

C.

non-broadcast multi-access networks (Hub and Spoke Frame Relay) using point-to- multipoint OSPF network type

D.

All networks type

 

Answer: B

 

 

QUESTION 19

What are two purposes of the BGP scan-time command? (Choose two.)

 

A.

to tune the BGP process which walks the BGP table and confirms the reachability of next hops

B.

to allow faster detection of downed BGP peers

C.

to improve BGP convergence time

D.

to tune the BGP update interval

E.

to decrease the effects of unstable routes by increasing the route suppression time

 

Answer: AC

Explanation:http://www.networkers-online.com/blog/2008/12/bgp-performance-tunning-convergence- stability-scalabilityand-nsf-part-2/

 

Background BGP scanner

It is responsible for BGP housekeeping by scanning both the BGP RIB and the IP RIB and cleaning and sorting things out.

BGP monitors the next hop of the installed routes to verify next-hop reachability and to select, install, and validate the BGP best path. By default, the BGP scanner polls the RIB for this information every 60 seconds.

 

During the 60 second time period between scan cycles, IGP instabilities or other network failures can cause temporarily black holes and routing loops.

 

NOTE With Cisco IOS the default timer is 60 seconds for the IPv4 address family and 15 seconds for the

 

VPNv4 address family in order to optimize the VPNs routing table convergence.

 

This timer can be controlled via the following command:

Router(config-router)#bgp scan-time <5-60>

 

 

QUESTION 20

DRAG DROP

 

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Answer: 

A.

 

B.

 

C.

 

D.

 

 

Answer:

 

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