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CCIE Routing and Switching Written Exam v5.1

 

QUESTION 191

DRAG DROP

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Correct Answer:

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QUESTION 192

Refer to the exhibit. What kind of load balancing is done on this router?

 

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A.

per-packet load balancing

B.

per-flow load
balancing

C.

per-label load balancing

D.

star round-robin load balancing

 

Correct Answer: A

Explanation:

Here we can see that for the same traffic source/destination pair of 10.0.0.1 to 14.0.0.2 there were a total of 100 packets (shown by second entry without the *) and that the packets were distributed evenly across the three different outgoing interfaces (34, 33, 33 packets, respectively.

 

 

QUESTION 193

Which Cisco IOS XE process administers routing and forwarding?

 

A.

Forwarding manager

B.

Interface manager

C.

Cisco IOS

D.

Host manager

 

Correct Answer: C

Explanation:

Some of the processes are listed in the table below:

Process

Purpose

Affected FRUs

SubPackage Mapping

Host Manager

Provides an interface between the IOS process and many of the information-gathering functions of the underlying platform kernel and operating system.

RP (one instance per RP)SIP (one instance per SIP)ESP (one instance per ESP) RPControlSIPBaseESPBase

Interface Manager

Provides an interface between the IOS process and the per-SPA interface processes on the SIP.

RP (one instance per RP)SIP (one instance per SIP)

RPControlSIPBase

IOS

The IOS process implements all forwarding and routing features for the router. RP (one per software redundancy instance per RP). Maximum of two instances per RP.

RPIOS

Forwarding Manager

Manages the downloading of configuration to each of the ESPs and the communication of forwarding plane information, such as statistics, to the IOS process. RP (one per software redundancy instance per RP). Maximum of two instances per RP.ESP (one per ESP)

RPControl

ESPBase

 

Reference: http://www.cisco.com/c/en/us/td/docs/routers/asr1000/configuration/guide/chassis/asrswcfg/Softwa re_Packaging_Architecture.html

 

 

QUESTION 194

Refer to the exhibit. Which command is configured on this router?

 

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A.

bgp update-delay 60

B.

neighbor 10.100.1.1 maximum-prefix 200

C.

neighbor 10.100.1.1 maximum-path 2

D.

neighbor 10.100.1.1 ebgp-multihop 2

 

Correct Answer: B

Explanation:

The BGP Maximum-Prefix feature allows you to control how many prefixes can be received from a neighbor. By default, this feature allows a router to bring down a peer when the number of received prefixes from that peer exceeds the configured Maximum-Prefix limit. This feature is commonly used for external BGP peers, but can be applied to internal BGP peers also. When the maximum number of prefixes have been received, the BGP sessions closes into the IDLE state.

Reference: http://www.cisco.com/c/en/us/support/docs/ip/border-gateway-protocol-bgp/25160-bgp-maximum-prefix.html

 

 

QUESTION 195

Which statement is true about MLD?

 

A.

MLD v1 gives hosts the ability to receive multicas
t packets from specific source addresses.

B.

All MLD messages are sent with a link-local IPv6 source address of FF02::D.

C.

The multicast address field is cleared to zero when sending an MLD report message.

D.

MLD is used by IPv6 routers to discover multicast listeners on a directly attached link.

 

Correct Answer: D

Explanation:

IPv6 Multicast Listener Discovery (MLD) is used by IPv6 devices to discover multicast listeners (nodes that want to receive multicast packets destined for specific multicast addresses) on directly attached links. There are two versions of MLD. MLD version 1 is based on version 2 of the IGMP for IPv4, and MLD version 2 is based on version 3 of the IGMP for IPv4. IPv6 multicast for Cisco software uses both MLD version 2 and MLD version 1.

Reference: http://www.cisco.com/c/en/us/td/docs/ios-xml/ios/ipmulti_lsm/configuration/xe-3s/imc-lsm-xe-3s-book/ipv6-mcast-mld-xe.html

 

 

QUESTION 196

Refer to the exhibit. Why is network 172.16.1.0/24 not installed in the routing table?

 

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A.

There is no ARP entry for 192.168.1.1.

B.

The router cannot ping 192.168.1.1.

C.

The neighbor 192.168.1.1 just timed out and BGP will flush this prefix the next time that the BGP scanner runs.

D.

There is no route for 192.168.1.1 in the routing table.

 

Correct Answer: D

Explanation:

Here we see that the next hop IP address to reach the 172.16.1.0 network advertised by the BGP peer is 192.168.1.1. However, the 192.168.1.1 IP is not in the routing table of R3 so it adds the route to the BGP table but marks it as inaccessible, as shown.

 

 

 

 

QUESTION 197

What is a reason for 6PE to use two MPLS labels in the data plane instead of one?

 

A.

6PE allows penultimate hop popping and has a requirement that all P routers do not have to be IPv6 aware.

B.

6PE does not allow penultimate hop popping.

C.

It allows MPLS traffic engineering to work in a 6PE network.

D.

It allows 6PE to work in an MPLS network where 6VPE is also deployed.

 

Correct Answer: A

Explanation:

Q. Why does 6PE use two MPLS labels in the data plane?

A. 6PE uses two labels:

The top label is the transport label, which is assigned hop-by-hop by the Label Distribution Protocol (LDP) or by MPLS traffic engineering (TE).

The bottom label is the label assigned by the Border Gateway Protocol (BGP) and advertised by the internal BGP (iBGP) between the Provider Edge (PE) routers.

When the 6PE was released, a main requirement was that none of the MPLS core routers (the P routers) had to be IPv6-aware. That requirement drove the need for two labels in the data plane.

There are two reasons why the 6PE needs both labels.

PHP Functionality

If only the transport label were used, and if penultimate hop popping (PHP) were used, the penultimate hop router (the P router) would need to understand IPv6. With PHP, this penultimate hop router would need to remove the MPLS label and forward the packet as an IPv6 packet. This P router would need to know that the packet is IPv6 because the P router would need to use the correct Layer 2 encapsulation type for IPv6. (The encapsulation type is different for IPv6 and IPv4; for example, for Ethernet, the encapsulation type is 0x86DD for IPv6, while it is 0x0800 for IPv4.) If the penultimate hop router is not IPv6-capable, it would likely put the Layer 2 encapsulation type for IPv4 for the IPv6 packet. The egress PE router would then believe that the packet was IPv4.

There is time-to-live (TTL) processing in both the IPv4 and IPv6 headers. In IPv6, the field is called Hop Limit. The IPv4 and IPv6 fields are at different locations in the headers. Also, the Header Checksum in the IPv4 header would also need to be changed; there is no Header Checksum field in IPv6. If the penultimate hop router is not IPv6-capable, it would cause the IPv6 packet to be malformed since the router expects to find the TTL field and Header Checksum field in the header. Because of these differences, the penultimate hop router would need to know it is an IPv6 packet. How would this router know that the packet is an IPv6 packet, since it did not assign a label to the IPv6 Forwarding Equivalence Class (FEC), and there is no encapsulation field in the MPLS header? It could scan for the first nibble after the label stack and determine that the packet is IPv6 if the value is 6. However, that implies that the penultimate hop router needs to be IPv6-capable. This scenario could work if the explicit null label is used (hence no PHP). However, the decision was to require PHP.

Load Balancing

Typical load balancing on a P router follows this process. The P router goes to the end of the label stack and determines if it is an IPv4 packet by looking at the first nibble after the label stack.

If the nibble has a value of 4, the MPLS payload is an IPv4 packet, and the P router load balances by hashing the source and destination IPv4 addresses.

If the P router is IPv6-capable and the value of the nibble is 6, the P router load balances by hashing the source and destination IPv6 addresses.

If the P router is not IPv6-capable and the value of the nibble is not 4 (it could be 6 if the packet is an IPv6 packet), the P router determines it is not an IPv4 packet and makes the load balancing decision based on the bottom label.

In the 6PE scenario, imagine there are two egress PE routers advertising one IPv6 prefix in BGP towards the ingress PE router. This IPv6 prefix would be advertised with two different labels in BGP. Hence, in the data plane, the bottom label would be either of the two labels. This would allow a P router to load balance on the bottom label on a per-flow basis. If 6PE used only the transport label to transport the 6PE packets through the MPLS core, the P routers would not be able to load balance these packets on a per-flow basis unless the P router
s were IPv6-capable. If the P routers were IPv6-capable, they could use the source and destination IPv6 addresses in order to make a load balancing decision.

Reference: http://www.cisco.com/c/en/us/support/docs/multiprotocol-label-switching-mpls/mpls/116061-qa-6pe-00.html

 

 

QUESTION 198

DRAG DROP

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Correct Answer:

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QUESTION 199

Which statement is true about IGMP?

 

A.

Multicast sources send IGMP messages to their first-hop router, which then generates a PIM join message that is then sent to the RP.

B.

Multicast receivers send IGMP messages to their first-hop router, which then forwards the IGMP messages to the RP.

C.

IGMP messages are encapsulated in PIM register messages and sent to the RP.

D.

Multicast receivers send IGMP messages to signal their interest to receive traffic for specific multicast groups.

 

Correct Answer: D

Explanation:

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In the example shown above, the receivers (the designated multicast group) are interested in receiving the video data stream from the source. The receivers indicate their interest by sending an Internet Group Management Protocol (IGMP) host report to the routers in the network. The routers are then responsible for delivering the data from the source to the receivers.

Reference: http://www.cisco.com/c/en/us/td/docs/ios/solutions_docs/ip_multicast/White_papers/mcst_ovr.html

 

 

QUESTION 200

Refer to the exhibit. Which two statements about the EEM applet configuration are true? (Choose two.)

 

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A.

The EEM applet runs before the CLI command is executed.

B.

The EEM applet runs after the CLI command is executed.

C.

The EEM applet requires a case-insensitive response.

D.

The running configuration is displayed only if the letter Y is entered at the CLI.

 

Correct Answer: AC

 

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