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QUESTION NO:1

Which two commands are required to enable multicast on a router, knowing that the receivers only

support IGMPv2? (Choose two.)

A. ip pim rp-address

B. ip pim ssm

C. ip pim sparse-mode

D. ip pim passive

Answer: A,C

Explanation:

Sparse mode logic (pull mode) is the opposite of Dense mode logic (push mode), in Dense mode

it is supposed that in every network there is someone who is requesting the multicast traffic so

PIM-DM routers begin by flooding the multicast traffic out of all their interfaces except those from

where a prune message is received to eliminate the


QUESTION NO:7

Which statement is true about TCN propagation?

A. The originator of the TCN immediately floods this information through the network.

B. The TCN propagation is a two step process.

C. A TCN is generated and sent to the root bridge.

D. The root bridge must flood this information throughout the network.

Answer: C

Explanation:

Explanation

New Topology Change Mechanisms

When an 802.1D bridge detects a topology change, it uses a reliable mechanism to first notify the

root bridge.

This is shown in this diagram:

Once the root bridge is aware of a change in the topology of the network, it sets the TC flag on the

BPDUs it sends out, which are then relayed to all the bridges in the network. When a bridge

receives a BPDU with the TC flag bit set, it reduces its bridging-table aging time to forward delay

seconds. This ensures a relatively quick flush of stale information. Refer to Understanding

Spanning-Tree Protocol Topology Changes for more information on this process. This topology

change mechanism is deeply remodeled in RSTP. Both the detection of a topology change and its

propagation through the network evolve.

Topology Change Detection

In RSTP, only non-edge ports that move to the forwarding state cause a topology change. This

means that a loss of connectivity is not considered as a topology change any more, contrary to

802.1D (that is, a port that moves to blocking no longer generates a TC). When a RSTP bridge

detects a topology change, these occur:

It starts the TC While timer with a value equal to twice the hello-time for all its non-edge

designated ports and its root port, if necessary.

It flushes the MAC addresses associated with all these ports.

Note: As long as the TC While timer runs on a port, the BPDUs sent out of that port have the TC

bit set.

BPDUs are also sent on the root port while the timer is active.

Topology Change Propagation

When a bridge receives a BPDU with the TC bit set from a neighbor, these occur:

It clears the MAC addresses learned on all its ports, except the one that receives the topology

change.

It starts the TC While timer and sends BPDUs with TC set on all its designated ports and root port

(RSTP no longer uses the specific TCN BPDU, unless a legacy bridge needs to be notified).

This way, the TCN floods very quickly across the whole network. The TC propagation is now a one

step process. In fact, the initiator of the topology change floods this information throughout the

network, as opposed to 802.1D where only the root did. This mechanism is much faster than the

802.1D equivalent. There is no need to wait for the root bridge to be notified and then maintain the

topology change state for the whole network for seconds.

In just a few seconds, or a small multiple of hello-times, most of the entries in the CAM tables of

the entire network (VLAN) flush. This approach results in potentially more temporary flooding, but

on the other hand it clears potential stale information that prevents rapid connectivity restitution.

Reference

http://www.cisco.com/en/US/tech/tk389/tk621/technologies_white_paper09186a0080094cfa.shtml


QUESTION NO:9

Which two are effects of connecting a network segment that is running 802.1D to a network

segment that is running 802.1w? (Choose two.)

A. The entire network switches to 802.1D and generates BPDUs to determine root bridge status. B.

A migration delay of three seconds occurs when the port that is connected to the 802.1D bridge

comes up.

C. The entire network reconverges and a unique root bridge for the 802.1D segment, and a root

bridge for the 802.1w segment, is chosen.

D. The first hop 802.1w switch that is connected to the 802.1D runs entirely in 802.1D compatibility

mode and converts the BPDUs to either 802.1D or 802.1w BPDUs to the 802.1D or 802.1w

segments of the network.

E. Classic 802.1D timers, such as forward delay and max-age, will only be used as a backup, and

will not be necessary if point-to-point links and edge ports are properly identified and set by the

administrator.

Answer: B,E

Explanation:

Each port maintains a variable that defines the protocol to run on the corresponding segment. A

migration delay timer of three seconds also starts when the port comes up. When this timer runs,

the current STP or RSTP mode associated to the port is locked. As soon as the migration delay

expires, the port adapts to the mode that corresponds to the next BPDU it receives. If the port

changes its mode of operation as a result of a BPDU received, the migration delay restarts.

802.1D works by the concept that the protocol had to wait for the network to converge before it

transitioned a port into the forwarding state. With Rapid Spanning Tree it does not have to rely on

any timers, the only variables that that it relies on is edge ports and link types.

Any uplink port that has an alternate port to the root can be directly placed into the forwarding

state (This is the Rapid convergence that you speak of “restored quickly when RSTP is already in

use?”). This is what happened when you disconnected the primary look; the port that was ALT,

moved to FWD immediately, but the switch also still needs to create a BDU with the TC bit set to

notify the rest of the network that a topology has occurred and all non-edge designated ports will

transition to BLK, LRN, and then FWD to ensure there are no loops in the rest of the network. This

is why if you have a host on a switchport, and you know for a fact that it is only one host, enable

portfast to configure the port as an edgeport so that it does not have to transition to all the STP

states.

Reference

http://www.cisco.com/en/US/tech/tk389/tk621/technologies_white_paper09186a0080094cfa.shtml


QUESTION NO:17

Which three combinations are valid LACP configurations that will set up a channel? (Choose

three.)

A. On/On

B. On/Auto

C. Passive/Active

D. Desirable/Auto

E. Active/Active

F. Desirable/Desirable

Answer: A,C,E

Explanation:


QUESTION NO:19

Which two options does Cisco PfR use to control the entrance link selection with inbound

optimization? (Choose two.)

A. Prepend extra AS hops to the BGP prefix.

B. Advertise more specific BGP prefixes (longer mask).

C. Add (prepend) one or more communities to the prefix that is advertised by BGP.

D. Have BGP dampen the prefix.

Answer: A,C

Explanation: PfR Entrance Link Selection Control Techniques

The PfR BGP inbound optimization feature introduced the ability to influence inbound traffic. A

network advertises reachability of its inside prefixes to the Internet using eBGP advertisements to

its ISPs. If the same prefix is advertised to more than one ISP, then the network is multihoming.

PfR BGP inbound optimization works best with multihomed networks, but it can also be used with

a network that has multiple connections to the same ISP. To implement BGP inbound

optimization, PfR manipulates eBGP advertisements to influence the best entrance selection for

traffic bound for inside prefixes. The benefit of implementing the best entrance selection is limited

to a network that has more than one ISP connection.

To enforce an entrance link selection, PfR offers the following methods:

BGP Autonomous System Number Prepend When an entrance link goes out-of-policy (OOP) due

to delay, or in images prior to Cisco IOS Releases 15.2(1) T1 and 15.1(2)S, and PfR selects a

best entrance for an inside prefix, extra autonomous system hops are prepended one at a time (up

to a maximum of six) to the inside prefix BGP advertisement over the other entrances. In Cisco

IOS Releases 15.2(1)T1, 15.1(2)S, and later releases, when an entrance link goes out-of policy

(OOP) due to unreachable or loss reasons, and PfR selects a best entrance for an inside prefix,

six extra autonomous system hops are prepended immediately to the inside prefix BGP

advertisement over the other entrances. The extra autonomous system hops on the other

entrances increase the probability that the best entrance will be used for the inside prefix. When

the entrance link is OOP due to unreachable or loss reasons, six extra autonomous system hops

are added immediately to allow the software to quickly move the traffic away from the old entrance

link. This is the default method PfR uses to control an inside prefix, and no user configuration is

required.

BGP Autonomous System Number Community Prepend

When an entrance link goes out-of-policy (OOP) due to delay, or in images prior to Cisco IOS

Releases 15.2

(1)T1 and 15.1(2)S, and PfR selects a best entrance for an inside prefix, a BGP prepend

community is attached one at a time (up to a maximum of six) to the inside prefix BGP

advertisement from the network to another autonomous system such as an ISP. In Cisco IOS

Releases 15.2(1)T1, 15.1(2)S, and later releases, when an entrance link goes out-of-policy (OOP)

due to unreachable or loss reasons, and PfR selects a best entrance for an inside prefix, six BGP

prepend communities are attached to the inside prefix BGP advertisement. The BGP prepend

community will increase the number of autonomous system hops in the advertisement of the

inside prefix from the ISP to its peers. Autonomous system prepend BGP community is the

preferred method to be used for PfR BGP inbound optimization because there is no risk of the

local ISP filtering the extra autonomous system hops. There are some issues, for example, not all

ISPs support the BGP prepend community, ISP policies may ignore or modify the autonomous

system hops, and a transit ISP may filter the autonomous system path. If you use this method of

inbound optimization and a change is made to an autonomous system, you must issue an

outbound reconfiguration using the “clear ip bgp” command.

Reference

http://www.cisco.com/en/US/docs/ios-xml/ios/pfr/configuration/15-2s/pfr-bgp-inbound.html#GUID-

F8A59E241D59-

4924-827D-B23B43D9A8E0

http://www.cisco.com/en/US/products/ps8787/products_ios_protocol_option_home.html


Latest 400-101 Dumps400-101 PDF Dumps400-101 VCE Dumps

QUESTION NO:22

Refer to the exhibit.

Which path is selected as best path?

A. path 1, because it is learned from IGP B.

path 1, because the metric is the lowest C.

path 2, because it is external

D. path 2, because it has the higher router ID

Answer: B

Explanation:


QUESTION NO:33

Which two OSPF LSA types are new in OSPF version 3? (Choose two.)

A. Link

B. NSSA external

C. Network link

D. Intra-area prefix

E. AS domain

Answer: A,D

Explanation:

New LSA Types

OSPFv3 carries over the seven basic LSA types we\’re familiar with from OSPFv2. However, the

type 1 and 2 LSAs have been re-purposed, as will be discussed in a bit. OSPFv3 also introduces

two new LSA types: Link and Intra-area Prefix.

Reference

http://packetlife.net/blog/2010/mar/2/ospfv2-versus-ospfv3/


QUESTION NO:38

Refer to the exhibit.

This is an MPLS VPN network with OSPF as the PE-CE routing protocol. Which statement is

correct?

A. The routing inside the VPN RED will never work correctly.

B. The routing inside the VPN RED can be enabled by configuring virtual links between the PE

routers.

C. The routing inside the VPN RED can be enabled by configuring area 0 inside the VRF on the

PE routers.

D. The routing inside the VPN RED will work without any special OSPF configuration.

E. The routing inside the VPN RED will work if the PE routers have a full mesh of sham-links

configured for VRF RED.

Answer: D Explanation:

http://www.cisco.com/en/US/docs/net_mgmt/vpn_solutions_center/1.1/user/guide/VPN_UG1.html


QUESTION NO:41

On a router, interface S0 is running EIGRPv6, and interface S1 is running OSPFv3. A

redistribution command is issued under OSPFv3, redistribute EIGRP 1 metric 20 under ipv6 router

ospf 1. What will happen after applying this redistribution command?

A. All routes showing up as D and D EX in the routing table will be redistributed into OSPFv3.

B. All routes showing up as D, D EX, and C in the routing table will be redistributed into OSPFv3.

C. All routes showing up as D and D EX in the routing table and the S0 interface will be

redistributed into OSPFv3.

D. All routes showing up as D in the routing table will be redistributed into OSPFv3.

E. All routes showing up as D EX in the routing table will be redistributed into OSPFv3.

Answer: A

Explanation:

D are EIGRP Internal Routes and D EX are EIGRP external routes. Both Internal and External

EIGRP routes will be redistributed with the configuration shown above


QUESTION NO:44

How is RPF used in multicast routing?

A. to prevent multicast packets from looping

B. to prevent PIM packets from looping

C. to instruct PIM where to send a (*, G) or (S, G) join message

D. to prevent multicast packets from looping and to instruct PIM where to send a (*, G) or (S, G)

join message

Answer: D

Explanation:


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