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QUESTION NO:6

Why would a rogue host that is running a DHCP server on a campus LAN network present a

security risk?

A. It may allocate IP addresses from an unknown subnet to the users.

B. All multicast traffic can be sniffed by using the DHCP multicast capabilities.

C. The CPU utilization of the first hop router can be overloaded by exploiting DHCP relay open

ports.

D. A potential man-in-the-middle attack can be used against the clients.

Answer: D

Explanation:


QUESTION NO:8

Which statement is true about loop guard?

A. Loop guard only operates on interfaces that are considered point-to-point by the spanning tree.

B. Loop guard only operates on root ports.

C. Loop guard only operates on designated ports.

D. Loop guard only operates on edge ports.

Answer: A

Explanation:

Explanation

Understanding How Loop Guard Works

Unidirectional link failures may cause a root port or alternate port to become designated as root if

BPDUs are absent. Some software failures may introduce temporary loops in the network. Loop

guard checks if a root port or an alternate root port receives BPDUs. If the port is receiving

BPDUs, loop guard puts the port into an inconsistent state until it starts receiving BPDUs again.

Loop guard isolates the failure and lets spanning tree converge to a stable topology without the

failed link or bridge.

You can enable loop guard per port with the set spantree guard loop command.

Note When you are in MST mode, you can set all the ports on a switch with the set spantree

global-defaults loop-guard command.

When you enable loop guard, it is automatically applied to all of the active instances or VLANs to

which that port belongs. When you disable loop guard, it is disabled for the specified ports.

Disabling loop guard moves all loop-inconsistent ports to the listening state.

If you enable loop guard on a channel and the first link becomes unidirectional, loop guard blocks

the entire channel until the affected port is removed from the channel. Figure 8-6 shows loop

guard in a triangle switch configuration.

Figure 8-6 Triangle Switch Configuration with Loop Guard

Figure 8-6 illustrates the following configuration:

Switches A and B are distribution switches.

Switch C is an access switch.

Loop guard is enabled on ports 3/1 and 3/2 on Switches A, B, and C.

Use loop guard only in topologies where there are blocked ports. Topologies that have no blocked

ports, which are loop free, do not need to enable this feature. Enabling loop guard on a root switch

has no effect but provides protection when a root switch becomes a nonroot switch.

Follow these guidelines when using loop guard:

Do not enable loop guard on PortFast-enabled or dynamic VLAN ports.

Do not enable PortFast on loop guard-enabled ports.

Do not enable loop guard if root guard is enabled.

Do not enable loop guard on ports that are connected to a shared link.

Note: We recommend that you enable loop guard on root ports and alternate root ports on access

switches.

Loop guard interacts with other features as follows:

Loop guard does not affect the functionality of UplinkFast or BackboneFast.

Root guard forces a port to always be designated as the root port. Loop guard is effective only if

the port is a root port or an alternate port. Do not enable loop guard and root guard on a port at the

same time.

PortFast transitions a port into a forwarding state immediately when a link is established. Because

a PortFast-enabled port will not be a root port or alternate port, loop guard and PortFast cannot be

configured on the same port. Assigning dynamic VLAN membership for the port requires that the

port is PortFast enabled. Do not configure a loop guard-enabled port with dynamic VLAN

membership.

If your network has a type-inconsistent port or a PVID-inconsistent port, all BPDUs are dropped

until the misconfiguration is corrected. The port transitions out of the inconsistent state after the

message age expires. Loop guard ignores the message age expiration on type-inconsistent ports

and PVID-inconsistent ports. If the port is already blocked by loop guard, misconfigured BPDUs

that are received on the port make loop guard recover, but the port is moved into the type-

inconsistent state or PVID-inconsistent state.

In high-availability switch configurations, if a port is put into the blocked state by loop guard, it

remains blocked even after a switchover to the redundant supervisor engine. The newly activated

supervisor engine recovers the port only after receiving a BPDU on that port.

Loop guard uses the ports known to spanning tree. Loop guard can take advantage of logical ports

provided by the Port Aggregation Protocol (PAgP). However, to form a channel, all the physical

ports grouped in the channel must have compatible configurations. PAgP enforces uniform

configurations of root guard or loop guard on all the physical ports to form a channel.

These caveats apply to loop guard:


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:12

Which two options are contained in a VTP subset advertisement? (Choose two.)

A. followers field

B. MD5 digest

C. VLAN information

D. sequence number

Answer: C,D

Explanation:

Subset Advertisements

When you add, delete, or change a VLAN in a Catalyst, the server Catalyst where the changes are

made increments the configuration revision and issues a summary advertisement. One or several

subset advertisements follow the summary advertisement. A subset advertisement contains a list

of VLAN information.

If there are several VLANs, more than one subset advertisement can be required in order to

advertise all the VLANs.

Subset Advertisement Packet Format

This formatted example shows that each VLAN information field contains information for a different

VLAN. It is ordered so that lowered-valued ISL VLAN IDs occur first:

Most of the fields in this packet are easy to understand. These are two clarifications:

Code


QUESTION NO:14

Which three options are features of VTP version 3? (Choose three.)

A. VTPv3 supports 8K VLANs.

B. VTPv3 supports private VLAN mapping.

C. VTPv3 allows for domain discovery.

D. VTPv3 uses a primary server concept to avoid configuration revision issues.

E. VTPv3 is not compatible with VTPv1 or VTPv2.

F. VTPv3 has a hidden password option.

Answer: B,D,F

Explanation:

Key Benefits of VTP Version 3

Much work has gone into improving the usability of VTP version 3 in three major areas:

The new version of VTP offers better administrative control over which device is allowed to update

other devices\’ view of the VLAN topology. The chance of unintended and disruptive changes is

significantly reduced, and availability is increased. The reduced risk of unintended changes will

ease the change process and help speed deployment.

Functionality for the VLAN environment has been significantly expanded. Two enhancements are

most beneficial for today\’s networks:


400-101 PDF Dumps400-101 VCE Dumps400-101 Exam Questions

QUESTION NO:15

Which three options are considered in the spanning-tree decision process? (Choose three.)

A. lowest root bridge ID

B. lowest path cost to root bridge

C. lowest sender bridge ID

D. highest port ID

E. highest root bridge ID

F. highest path cost to root bridge

Answer: A,B,C

Explanation:

Configuration bridge protocol data units (BPDUs) are sent between switches for each port.

Switches use s four step process to save a copy of the best BPDU seen on every port. When a

port receives a better BPDU, it stops sending them. If the BPDUs stop arriving for 20 seconds

(default), it begins sending them again.

Step 1 Lowest Root Bridge ID (BID)

Step 2 Lowest Path Cost to Root Bridge

Step 3 Lowest Sender BID

Step 4 Lowest Port ID

Reference

Cisco General Networking Theory Quick Reference Sheets


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:


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:28

Which two orders in the BGP Best Path Selection process are correct? (Choose two.)

A. Higher local preference, then lowest MED, then eBGP over iBGP paths

B. Higher local preference, then highest weight, then lowest router ID

C. Highest weight, then higher local preference, then shortest AS path

D. Lowest origin type, then higher local preference, then lowest router ID

E. Highest weight, then higher local preference, then highest MED

Answer: A,C

Explanation:


QUESTION NO:32

Which two tunneling techniques support IPv6 multicasting? (Choose two.)

A. 6to4

B. 6over4

C. ISATAP

D. 6PE

E. GRE

Answer: B,E

Explanation:

When IPv6 multicast is supported (over a 6to4 tunnel), an IPv6 multicast routing protocol must be

used

Restrictions for Implementing IPv6 Multicast

IPv6 multicast for Cisco IOS software uses MLD version 2. This version of MLD is fully backward-

compatible with MLD version 1 (described in RFC 2710). Hosts that support only MLD version 1

will interoperate with a router running MLD version 2. Mixed LANs with both MLD version 1 and

MLD version 2 hosts are likewise supported.

IPv6 multicast is supported only over IPv4 tunnels in Cisco IOS Release 12.3(2)T, Cisco IOS

Release 12.2

(18)S, and Cisco IOS Release 12.0(26)S.

When the bidirectional (bidir) range is used in a network, all routers in that network must be able to

understand the bidirectional range in the bootstrap message (BSM).

IPv6 multicast routing is disabled by default when the ipv6 unicast-routing command is configured.

On Cisco Catalyst 6500 and Cisco 7600 series routers, the ipv6 multicast-routing also must be

enabled in order to use IPv6 unicast routing

Reference http://www.cisco.com/web/about/ac123/ac147/ac174/ac197/

about_cisco_ipj_archive_article09186a00800c830a.html

http://www.cisco.com/en/US/docs/ios/ipv6/configuration/guide/ip6-multicast.html

https://supportforums.cisco.com/thread/183386


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