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QUESTION NO:2

A branch router is configured with an egress QoS policy that was designed for a total number of

10 concurrent VOIP calls.

Due to expansion, 15 VOIP calls are now running over the link, but after the 14th call was

established, all calls were affected and the voice quality was dramatically degraded.

Assuming that there is enough bandwidth on the link for all of this traffic, which part of the QoS

configuration should be updated due to the new traffic profile?

A. Increase the shaping rate for the priority queue. B.

Remove the policer applied on the priority queue. C.

Remove the shaper applied on the priority queue. D.

Increase the policing rate for the priority queue.

Answer: D

Explanation:


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:13

Which two statements are true about traffic shaping? (Choose two.)

A. Out-of-profile packets are queued.

B. It causes TCP retransmits.

C. Marking/remarking is not supported.

D. It does not respond to BECN and ForeSight Messages.

E. It uses a single/two-bucket mechanism for metering.

Answer: A,C

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


QUESTION NO:20

Refer to the exhibit.

What is the potential issue with this configuration?

A. There is no potential issue; OSPF will work fine in any condition.

B. Sub-optimal routing may occur since there is no area 1 adjacency between the ABRs.

C. This is a wrong OSPF configuration because all routers must be in area 0 only.

D. This is a wrong OSPF configuration because /30 requires 0.0.0.3 wild card.

Answer: B

Explanation:


400-101 PDF Dumps400-101 Study Guide400-101 Braindumps

QUESTION NO:24

Refer to the exhibit.

R1 is not learning about the 172.16.10.0 subnet from the BGP neighbor R2 (209.165.202.130).

What can be done so that R1 will learn about this network?

A. Disable auto-summary on R2.

B. Configure an explicit network command for the 172.16.10.0 subnet on R2.

C. Subnet information cannot be passed between IBGP peers.

D. Disable auto-summary on R1.

Answer: B

Explanation:

By default, BGP does not accept subnets redistributed from IGP. To advertise and carry subnet

routes in BGP, use an explicit network command or the no auto-summary command. If you disable

auto-summarization and have not entered a network command, you will not advertise network

routes for networks with subnet routes unless they contain a summary route.

Reference

http://www.cisco.com/en/US/docs/ios/11_3/np1/command/reference/1rbgp.html


QUESTION NO:25

Refer to the exhibit.

After a link flap in the network, which two EIGRP neighbors will not be queried for alternative

paths? (Choose two.)

A. 192.168.1.1

B. 192.168.3.7

C. 192.168.3.8

D. 192.168.3.6

E. 192.168.2.1

F. 192.168.3.9

Answer: B,C

Explanation:

Explanation

Both 192.168.3.7 and 192.168.3.8 are in an EIGRP Stub area

The Enhanced Interior Gateway Routing Protocol (EIGRP) Stub Routing feature improves network

stability, reduces resource utilization, and simplifies stub router configuration.

Stub routing is commonly used in a hub and spoke network topology. In a hub and spoke network,

one or more end (stub) networks are connected to a remote router (the spoke) that is connected to

one or more distribution routers (the hub). The remote router is adjacent only to one or more

distribution routers. The only route for IP traffic to follow into the remote router is through a

distribution router. This type of configuration is commonly used in WAN topologies where the

distribution router is directly connected to a WAN. The distribution router can be connected to

many more remote routers. Often, the distribution router will be connected to 100 or more remote

routers. In a hub and spoke topology, the remote router must forward all nonlocal traffic to a

distribution router, so it becomes unnecessary for the remote router to hold a complete routing

table. Generally, the distribution router need not send anything more than a default route to the

remote router.

When using the EIGRP Stub Routing feature, you need to configure the distribution and remote

routers to use EIGRP, and to configure only the remote router as a stub. Only specified routes are

propagated from the remote (stub) router. The router responds to queries for summaries,

connected routes, redistributed static routes, external routes, and internal routes with the message

“inaccessible.” A router that is configured as a stub will send a special peer information packet to

all neighboring routers to report its status as a stub router. Any neighbor that receives a packet

informing it of the stub status will not query the stub router for any routes, and a router that has a

stub peer will not query that peer. The stub router will depend on the distribution router to send the

proper updates to all peers.

Reference

http://www.cisco.com/en/US/docs/ios/12_0s/feature/guide/eigrpstb.html#wp1021949


QUESTION NO:26

Refer to the exhibit.

Why is AS 65333 in parentheses?

A. It is an external AS.

B. It is a confederation AS.

C. It is the AS of a route reflector.

D. It is our own AS.

E. A route map has been applied to this route.

F. The BGP next hop is unreachable.

Answer: B

Explanation:


QUESTION NO:40

Which three fields are optional in an OSPFv3 external LSA? (Choose three.)

A. Forwarding Address

B. External Route

C. Reference Link-State ID

D. Option

E. Prefix Options

Answer: A,B,C

Explanation:

AS-External LSA

As with OSPFv2, the AS-External LSA advertises prefixes external to the OSPF routing domain;

one LSA is required for each external prefix advertised. However, the format of the OSPFv3 As-

External LSA (Figure 9-10) is different from its OSPFv2 counterpart.

Figure 9-10. OSPFv3 AS-External LSA

Reference

http://fengnet.com/book/CCIE Professional Development Routing TCPIP Volu

me I/images/09fig10_alt.jpg


QUESTION NO:43

Which two multicast address ranges are assigned as source-specific multicast destination

addresses and are reserved for use by source-specific applications and protocols? (Choose two.)

A. 232.0.0.0/8

B. 239.0.0.0/8

C. 232.0.0.0/4

D. FF3x::/32

E. FF2x::/32

F. FF3x::/16

Answer: A,D

Explanation: Source-specific multicast (SSM) is a method of delivering multicast packets in which

the only packets that are delivered to a receiver are those originating from a specific source

address requested by the receiver. By so limiting the source, SSM reduces demands on the

network and improves security.

SSM requires that the receiver specify the source address and explicitly excludes the use of the (*,

G) join for all multicast groups in RFC 3376, which is possible only in IPv4\’s IGMPv3 and IPv6\’s

MLDv2.

Source-specific multicast is best understood in contrast to any-source multicast (ASM). In the

ASM service model a receiver expresses interest in traffic to a multicast address. The multicast

network must

1. discover all multicast sources sending to that address, and

2. route data from all sources to all interested receivers.

This behavior is particularly well suited to groupware applications where

1. all participants in the group want to be aware of all other participants, and

2. the list of participants is not known in advance.

The source discovery burden on the network can become significant when the number of sources

is large.

In the SSM service model, in addition to the receiver expressing interest in traffic to a multicast

address, the receiver expresses interest in receiving traffic from only one specific source sending

to that multicast address.

This relieves the network of discovering many multicast sources and reduces the amount of

multicast routing information that the network must maintain.

SSM requires support in last-hop routers and in the receiver\’s operating system. SSM support is

not required in other network components, including routers and even the sending host. Interest in

multicast traffic from a specific source is conveyed from hosts to routers using IGMPv3 as

specified in RFC 4607.

SSM destination addresses must be in the ranges 232.0.0.0/8 for IPv4 or FF3x::/96 for IPv6.

Reference

http://en.wikipedia.org/wiki/Source-specific_multicast


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