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CCIE Routing and Switching Written Exam v5.1

 

QUESTION 551

Which two options are valid for the number of bytes in a BGP AS number? (Choose two.)

 

A.

2 bytes

B.

4 bytes

C.

6 bytes

D.

8 bytes

E.

16 bytes

 

Correct Answer: AB

Explanation:

During the early time of BGP development and standardization, it was assumed that availability of a 16 bit binary number to identify the Autonomous System (AS) within BGP would have been more than sufficient. The 16 bit AS number, also known as the 2-byte AS number, provides a pool of 65536 unique Autonomous System numbers. The IANA manages the available BGP Autonomous System Numbers (ASN) pool, with the assignments being carried out by the Regional Registries. The current consumption rate of the publicly available AS numbers suggests that the entire public 2-byte ASN pool will be fully depleted. A solution to this depletion is the expansion of the existing 2-byte AS number to a 4-byte AS number, which provides a theoretical 4,294,967,296 unique AS numbers. ARIN has made the following policy changes in conjunction with the adoption of the solution.

The Cisco IOS BGP “4-byte ASN” feature allows BGP to carry a Autonomous System Number (ASN) encoded as a 4-byte entity. The addition of this feature allows an operator to use an expanded 4-byte AS number granted by IANA.

 

 

QUESTION 552

Which option describes a limitation of Embedded Packet Capture?

 

A.

It can capture data only on physical interfaces and subinterfaces.

B.

It can store only packet data.

C.

It can capture multicast packets only on ingress.

D.

It can capture multicast packets only on egress.

 

Correct Answer: C

Explanation:

Restrictions for Embedded Packet Capture

Reference: http://www.cisco.com/c/en/us/td/docs/ios-xml/ios/epc/configuration/15-mt/epc-15-mt-book/nm-packet-capture.html

 

 

QUESTION 553

DRAG DROP

Drag and drop the DMVPN command on the left to the corresponding function on the right.

 

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Correct Answer:

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QUESTION 554

Which two statements are characteristics of Ethernet private LAN circuits? (Choose two.)

 

A.

They support communication between two or more customer endpoints.

B.

They utilize more than one bridge domain.

C.

They support point-to-multipoint EVC.

D.

They support multipoint-to-multipoint EVC.

 

Correct Answer: AD

Explanation:

An Ethernet Private LAN (EPLAN) is a multipoint–to–multipoint EVC. EPLAN is an EVC that supports communication between two or more UNIs. In EPLAN, only one EVC can exist on a port and the port can have only one EFP.

Reference:

https://www.cisco.com/c/en/us/td/docs/optical/cpt/r9_3/configuration/guide/cpt93_configuration/cpt93_configuration_chapter_0100.pdf

 

 

QUESTION 555

Which three types of traffic are protected when you implement IPsec within an IPv6-in-IPv4 tunnel? (Choose three.)

 

A.

IPv6 link-local traffic

B.

IPv6 multicast traffic

C.

IPv6 unicast traffic

D.

IPv4 tunnel control traffic

E.

IPv4 broadcast traffic

F.

IPv6 broadcast traffic

 

Correct Answer: ABC

 

 

QUESTION 556

Which three protocols can use enhanced object tracking? (Choose three.)

 

A.

HSRP

B.

Proxy-ARP

C.

VRRP

D.

GLBP

E.

NTP

F.

DHCP

 

Correct Answer: ACD

Explanation:

The Enhanced Object Tracking feature separates the tracking mechanism from HSRP and creates a separate standalone tracking process that can be used by other processes and HSRP. This feature allows tracking of other objects in addition to the interface line-protocol state. A client process such as HSRP, Virtual Router Redundancy Protocol (VRRP), or Gateway Load Balancing Protocol (GLBP), can register its interest in tracking objects and then be notified when the tracked object changes state.

Reference: http://www.cisco.com/c/en/us/td/docs/ios-xml/ios/ipapp/configuration/15-mt/iap-15-mt-book/iap-eot.html

 

 

QUESTION 557

Which two types of traffic are blocked when the storm control threshold for multicast traffic is reached on a port? (Choose two.)

 

A.

BPDU

B.

OSPF

C.

CDP

D.

IS-IS

E.

LLDP

 

Correct Answer: BD

 

 

QUESTION 558

Which two loop-prevention mechanisms are implemented in BGP? (Choose two.)

 

A.

A route with its own AS in the AS_PATH is dropped automatically if the route reenters its own AS.

B.

A
route with its own cluster ID in the CLUSTER_LIST is dropped automatically when the route reenters its own AS.

C.

The command bgp allowas-in enables a route with its own AS_PATH to be dropped when it reenters its own AS.

D.

The command bgp bestpath as-path ignore enables the strict checking of AS_PATH so that they drop routes with their own AS in the AS_PATH.

E.

The command bgp bestpath med missing-as-worst assigns the smallest possible MED, which directly prevents a loop.

 

Correct Answer: AB

Explanation:

When dealing with the possibility of routing updates making their way back into an AS, BGP relies on the information in the AS_path for loop detection. An update that tries to make its way back into the AS it was originated from will be dropped by the border router.

With the introduction of route reflectors, there is a potential for having routing loops within an AS. A routing update that leaves a cluster might find its way back inside the cluster. Loops inside the AS cannot be detected by the traditional AS_path approach because the routing updates have not left the AS yet. BGP offers two extra measures for loop avoidance inside an AS when route reflectors are configured.

Using an Originator ID

The originator ID is a 4-byte, optional, nontransitive BGP attribute (type code 9) that is created by the route reflector. This attribute carries the router ID of the originator of the route in the local AS. If, because of poor configuration, the update comes back to the originator, the originator ignores it.

Using a Cluster List

The cluster list is an optional, nontransitive BGP attribute (type code 10). Each cluster is represented with a cluster ID.

A cluster list is a sequence of cluster IDs that an update has traversed. When a route reflector sends a route from its clients to nonclients outside the cluster, it appends the local cluster ID to the cluster list. If the route reflector receives an update whose cluster list contains the local cluster ID, the update is ignored. This is basically the same concept as the AS_path list applied between the clusters inside the AS.

Reference: http://borg.uu3.net/cisco/inter_arch/page11.html

 

 

QUESTION 559

Which two statements about the default SNMP configuration are true? (Choose two.)

 

A.

The SNMP agent is enabled.

B.

The SNMP trap receiver is configured.

C.

All SNMP notification types are sent.

D.

SNMPv1 is the default version.

E.

SNMPv3 is the default version.

Correct Answer: CD

Explanation:

Default SNMP Configuration

Feature

Default Setting

SNMP agent

Enabled

SNMP community strings

Read-Only: Public

Read-Write. Private

Read-Write-all: Secret

SNMP trap receiver

None configured

SNMP traps

None enabled

SNMP version

If no version keyword is present, the default is version 1.

SNMPv3 authentication

If no keyword is entered, the default is the noauth (noAuthNoPriv) security level.

SNMP notification type

If no type is specified, all notifications are sent.

 

Reference: http://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst2950/software/release/12-1_19_ea1/configuration/guide/2950scg/swsnmp.html

 

 

QUESTION 560

Refer to the exhibit. Which two statements about the implementation are true? (Choose two.)

 

clip_image006

 

A.

The PPP multilink protocol header is omitted on delay-sensitive packets.

B.

The maximum number of fragments is 1.

C.

Small real-time packets are multilink-encapsulated.

D.

< font style="font-size: 10pt" color="#000000">A transmit queue is provided for smaller packets.

 

Correct Answer: AD

Explanation:

Previous implementations of Cisco IOS Multilink PPP (MLP) include support for Link

Fragmentation Interleaving (LFI). This feature allows the delivery of delay-sensitive packets, such as the packets of a Voice call, to be expedited by omitting the PPP Multilink Protocol header and sending the packets as raw PPP packets in between the fragments of larger data packets. This feature works well on bundles consisting of a single link. However, when the bundle contains multiple links there is no way to keep the interleaved packets in sequence with respect to each other.

The Multiclass Multilink PPP (MCMP) feature in Cisco IOS Release 12.2(13)T addresses the limitations of MLP LFI on bundles containing multiple links by introducing multiple data classes. With multiclass multilink PPP interleaving, large packets can be multilink-encapsulated and fragmented into smaller packets to satisfy the delay requirements of real-time voice traffic; small real-time packets, which are not multilink encapsulated, are transmitted between fragments of the large packets. The interleaving feature also provides a special transmit queue for the smaller, delay-sensitive packets, enabling them to be transmitted earlier than other flows. Interleaving provides the delay bounds for delay-sensitive voice packets on a slow link that is used for other best-effort traffic.

References:

http://www.cisco.com/c/en/us/td/docs/ios/dial/configuration/guide/12_4t/dia_12_4t_book/dia_multiclass_link_ppp.pdf

http://www.cisco.com/c/en/us/td/docs/routers/access/500/520/software/configuration/guide/520_SCG_Book/520scg_concepts.html

 

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