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Building Cisco Multilayer Switched
Networks (BCMSN)
Exam 642-811


Edition 2.0







© Copyrights 1998-2005 Fravo Technologies. All Rights Reserved.
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Q1. Which feature will put a switch port into the error-disabled state upon receipt of Spanning Tree
data messages, requiring a network administrator to manually put the port back in service?

A. Loop Guard
B. Port Fast
C. BDPU Guard
D. Root Guard
E. BDPU Filtering

Answer: C

Explanation:
Understanding BPDU Guard
The BPDU guard feature can be globally enabled on the switch or can be enabled per interface, but
the feature operates with some differences.
At the global level, you can enable BPDU guard on Port Fast-enabled ports by using the spanning-
tree portfast bpduguard default global configuration command. Spanning tree shuts down ports
that are in a Port Fast-operational state. In a valid configuration, Port Fast-enabled ports do not
receive BPDUs. Receiving a BPDU on a Port Fast-enabled port signals an invalid configuration, such
as the connection of an unauthorized device, and the BPDU guard feature puts the port in the
error-disabled state.

Reference:
/>09186a008017ff97.html



Q2. Which method of Layer 3 switching uses a forwarding information base (FIB)?

A. Route caching
B. Flow-based switching
C. Demand-based switching
D. Topology-based switching

Answer: A

Explanation: Cisco Express Forwarding reindexes the routing table into a new table called a
Forward Information Base (FIB). The FIN is an entry-for-entry match of the routing table that has
been reindexed via a binary search algorithm called a Patricia Tree.

Reference: Building Cisco Multilayer Switched Networks (Ciscopress) page 412



Q3. Which are two closely related standards specifically designed for data transmission over fiber
optic networks? (Choose two.)

A. FDDI
B. SONET
C. SDH
D. DSL
E. ATM
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Answer: B, E

Explanation: Synchronous Digital Hierarchy. The European standard that defines a rate and format
for transmission of optical signals over fiber using ATM and SONET. In contrast to PDH, SDH
provides for a synchronous multiplexing scheme.

Reference:
/>8655.html#998751



Q4. Access Control List (ACL) processing in some Cisco switches is done in hardware. What two
actions will take place when the hardware reaches capacity to store ACLs? (Choose two.)

A. Performance is increased.
B. Performance is decreased.
C. Packets are dropped.
D. Packet filtering will be accomplished.

Answer: B, D

Explanation:
Determining if the ACL Configuration Fits in Hardware:
As previously stated, ACL processing in the Catalyst 3550 switch is mostly accomplished in
hardware. However, if the hardware reaches its capacity to store ACL configurations, the switch
software attempts to fit a simpler configuration into the hardware. This simpler configuration does
not do all the filtering that has been configured, but instead sends some or all packets to the CPU
to be filtered by software. In this way, all configured filtering will be accomplished, but
performance is greatly decreased when the filtering is done in software.

Reference:
/>9186a008007e701.html



Q5. Which well-defined routing protocol would a network administrator configure on multicast
routes when member routes are widely dispersed?

A. Distance Vector Multicast Routing Protocol (DVMRP)
B. Protocol Independent Multicast Dense Mode (PIM-DM)
C. Multicast Open Shortest Path First (MOSPF)
D. Protocol Independent Multicast Sparse Mode (PIM-SM)
E. Core-Based Trees (CBT)

Answer: D

Explanation: Multicast routing protocols fall into two categories: Dense-mode (DM) and Sparse-
mode (SM). DM protocols assume that almost all routers in the network will need to distribute
multicast traffic for each multicast group (for example, almost all hosts on the network belong to
each multicast group). Accordingly, DM protocols build distribution trees by initially flooding the
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entire network and then pruning back the small number of paths without receivers. SM protocols
assume that relatively few routers in the network will be involved in each multicast. The hosts
belonging to the group are widely dispersed, as might be the case for most multicasts in the
Internet. Therefore, SM protocols begin with an empty distribution tree and add branches only as
the result of explicit requests to join the distribution.

Reference:
/>ml



Q6. Drag and drop the type of flow mask used with Multiplayer Switching (MLS) in the options
column to the statement that defines its character in the target column.





Answer:

Destination-IP - Used when no access list are configured
Source-Destination–IP - Used when standard access list is configured
IP-Flow - Used when extended access list is configured

Explanation:
Flow Mask:
• Destination-IP: This mode is used if no access list are configured on any of the MLS router
interfaces.
• Source-Destination–IP: This mode is used if there is a standard access list on any of the
MLS interfaces.
• IP-Flow: This mode is used if there is an extended access list on any MLS interfaces.

Reference: Building Cisco Multilayer Switched Networks (Ciscopress) page 234-235



Q7. Which QoS technique avoids the problems that occur when tail drops is used as the congestion
avoidance mechanism on the router?

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A. RSVP
B. WRED
C. CAR
D. CBWFQ

Answer: B

Explanation: With class-based QoS queuing, you can create up to 64 classes for an interface.
(Unlike WFQ, queues are not automatically based on the packet's ToS value.) Class-based QoS
queuing also lets you control the drop mechanism used when congestion occurs on the interface.
You can use WRED for the drop mechanism, and configure the WRED queues, to ensure that high-
priority packets within a class are given the appropriate weight. If you use tail drop, all packets
within a class are treated equally, even if the ToS values are not equal.

Reference:
/>0800e0a04.html



Q8. Which technology manages multicast traffic at Layer 2 by configuring Layer 2 LAN interfaces
dynamically to forward multicast only to those interfaces that want to receive it?

A. IGMP
B. IGMP snooping
C. PIM-DIM
D. DVMRP
E. MOSPF

Answer: B

Explanation:
Understanding IGMP Snooping
In subnets where you have configured either IGMP (see "Configuring IP Multicast Layer 3
Switching") or the IGMP querier (see the "Enabling the IGMP Querier" section), IGMP snooping
manages multicast traffic at Layer 2 by configuring Layer 2 LAN interfaces dynamically to forward
multicast traffic only to those interfaces that want to receive it.

Reference:
/>9186a00800f4ff2.html



Q9. Exhibit:


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Use the following information from switch SwitchA:

Port Mode Encapsulation Status Native VLAN
fa0/1 desirable n-802.1q trunking 5

Port VLANs is allowed on trunk
fa0/1 1-100, 102-1005

Port VLANs is owned and active in management domain
fa0/1 1-6. 8-100, 102-15, 197-999, 1002-1005

Port VLANs in spanning tree forwarding state and not pruned
fa0/1 1-6, 8-100, 102-105, 108-999, 1002-1005

The network operations center has received a call stating that users in VLAN 107 are unable to
access resources through Router Router1.

From this information contained in the graphic, what is the cause of this problem?

A. VLAN 107 does not exist on switch SwitchA.
B. VTP is pruning VLAN 107.
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C. VLAN 107 is not configured on the trunk.
D. Spanning tree is not enabled on VLAN 107.

Answer: D


Q10. Which two table types are CEF components? (Choose two.)

A. Forwarding information base
B. Adjacency tables
C. Neighbor tables
D. Caching tables
E. Route tables

Answer: A, B

Explanation: There are two Cisco Express Forwarding components:
• Forwarding Information Base
• Adjacency table

Reference: Building Cisco Multilayer Switched Networks (Ciscopress) page 412

Q11. What is a characteristic of a VLAN map that does not contain a match clause?

A. Implicit deny feature at end of list.
B. Implicit forward feature at end of list.
C. Can only be implemented by the input direction within the VLAN.
D. Can only be implemented by the output direction within the VLAN.

Answer: A

Explanation: Each VLAN access map can consist of one or more map sequences, each sequence
with a match clause and an action clause. The match clause specifies IP, IPX, or MAC ACLs for
traffic filtering and the action clause specifies the action to be taken when a match occurs. When a
flow matches a permit ACL entry the associated action is taken and the flow is not checked against
the remaining sequences. When a flow matches a deny ACL entry, it will be checked against the
next ACL in the same sequence or the next sequence. If a flow does not match any ACL entry and
at least one ACL is configured for that packet type, the packet is denied.

Reference:
/>9186a008007f4d4.html



Q12. As a design rule, what is the maximum time that should be allowed for a voice packet to
cross a network?

A. 60 milliseconds
B. 120 milliseconds

C. 150 milliseconds
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D. 210 milliseconds

Answer: C

Explanation: Delay is the time it takes for VoIP packets to travel between two endpoints and you
should design networks to minimize this delay. However, because of the speed of network links and
the processing power of intermediate devices, some delay is expected. The human ear normally
accepts up to about 150 milliseconds (ms) of delay without noticing problems (the ITU's G.114
standard recommends no more than 150 ms of one-way delay).

Reference:
/>80e7.html



Q13. What information do CGMP-enabled switches and routers exchange using the CGMP protocol?

A. CAM table changes.
B. Summarized IGMP information.
C. Multicast join and leave events.
D. Multicast group to port assignments.

Answer: C

Explanation: CGMP is based on a client/server model. The router is considered a CGMP server, with

the switch taking on the client role. The basis of CGMP is that the IP multicast router sees all ICMP
packets and therefore can inform the switch when specific hosts join or leave multicast groups. The
switch then uses this information to construct a forwarding table.

Reference: Building Cisco Multilayer Switched Networks (Ciscopress) page 306



Q14. TACACS+ uses which of the following protocols to communicate?

A. UDP
B. CDP
C. TCP
D. DES

Answer: C

Explanation: RADIUS uses UDP while TACACS+ uses TCP. TCP offers several advantages over UDP.
TCP offers a connection-oriented transport, while UDP offers best-effort delivery. RADIUS requires
additional programmable variables such as re-transmit attempts and time-outs to compensate for
best-effort transport, but it lacks the level of built-in support that a TCP transport offers.

Reference:




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Q15. What are three possible router states of HSRP routers on an LAN? (Choose three.)

A. Standby
B. Established
C. Active
D. Idle
E. Backup
F. Init

Answer: A, C, F

Explanation: Using HSRP, a set of routers works in concert to present the illusion of a single virtual
router to the hosts on the LAN. This set is known as an HSRP group or a standby group. A single
router elected from the group is responsible for forwarding the packets that hosts send to the
virtual router. This router is known as the Active router. Another router is elected as the Standby
router. In the event that the Active router fails, the Standby assumes the packet-forwarding duties
of the Active router. Although an arbitrary number of routers may run HSRP, only the Active router
forwards the packets sent to the virtual router.

Reference:




Q16. A customer’s requirement states that they only need to carry VLANs 1,2,10,20 on a trunk.
VLANs 1,2,3,4,10,20,50 are currently active in the network. Which two of the following commands
can be used to accomplish this requirement? (Choose two.)

A. switchport trunk allowed vlan add 1,2,10,20

B. switchport trunk disallowed vlan add 3,4,50
C. switchport trunk disallowed vlan remove 3,4,50
D. switchport trunk allowed vlan remove 3,4,50
E. switchport trunk allowed vlan except 1,2,10,20
F. switchport trunk allowed vlan except 3,4,50

Answer: A, D

Explanation:
switchport trunk allowed vlan vlan_list

The vlan_list format is all | none | [add | remove | except] vlan_atom[,vlan_atom...], where:

• all specifies all VLANs from 1 to 4094. This keyword is not supported on commands that do
not permit all VLANs in the list to be set at the same time.
• none indicates an empty list. This keyword is not supported on commands that require
certain VLANs to be set or at least one VLAN to be set.
• add adds the defined list of VLANs to those currently set, instead of replacing the list.
• remove removes the defined list of VLANs from those currently set, instead of replacing the
list.
• except lists the VLANs that should be calculated by inverting the defined list of VLANs.
• vlan_atom is either a single VLAN number from 1 to 4094 or a continuous range of VLANs
described by two VLAN numbers, the lesser one first, separated by a hyphen.

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Reference:
/>09186a0080144e79.html#1022676

Q17. In a Cisco switch with redundant power supplies of the same wattage, how is the total power
available to the switch provided when both supplies are operating normally? (Choose two.)

A. Total combined power of both supplies.
B. Total power of one supply.
C. Total power required is shared nearly equally by both supplies.
D. Total power is the sum of one-half of total power of both supplies.

Answer: C, D

Explanation: Specifying the redundant keyword enables redundancy. In a redundant configuration,
the total power drawn from both supplies is at no time greater than the capability of one supply. If
one supply malfunctions, the other supply can take over the entire system load. When you install
and turn on two power supplies, each
concurrently provides approximately half of the required power to the system. Load sharing and
redundancy are enabled automatically; no software configuration is required.

Reference:
/>9186a008007e6f6.html



Q18. In the 20/80 model, only 20 percent of traffic remains local to the workgroup LAN, and 80
percent of the traffic leaves the local network. Which two factors have contributed to this traffic
pattern? (Choose two.)

A. The Internet

B. Local servers
C. Server farms
D. Localized applications
E. More powerful desktop PC’s

Answer: C, D

Explanation: This geographic location can be as large as an entire building or as small as a single
switch inside a wiring closet. In a geographic VLAN structure, it is typical to find 80 percent of the
traffic remote to the user (server farms and so on) and 20 percent of the traffic local to the user
(local server, printers, and so on).

Reference: Building Cisco Multilayer Switched Networks (Ciscopress) page 93



Q19. What are four basic security measures that should be implemented on every device at every
layer of the hierarchical model? (Choose four.)

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A. Managed remote access
B. Password protection
C. Security surveillance
D. Privilege levels
E. Physical security
F. Inventory audit

Answer: A, B, D, E

Explanation: The policy to control access to network devices should be one of the first components
of the access policy. All devices at every layer of the campus network should have a plan to provide
for the following:
• Physical security
• Passwords
• Privilege levels to allow limited access to a network device
• Limiting virtual terminal or telnet access

Reference: Building Cisco Multilayer Switched Networks (Ciscopress) page 368



Q20. How does a non-Root switch choose its Root Port?

A. It chooses the port with the lowest cumulative Root Path Cost to the Root Bridge.
B. It chooses the port with the highest cumulative Root Path Cost to the Root Bridge.
C. The port receives an inferior BPDU from a neighboring switch on a shard LAN segment.
D. The port receives a BPDU announcing a higher Root Path Cost from a neighboring switch on a
shared LAN segment.

Answer: A

Explanation: The spanning tree Protocol uses the information found in the BPDUs to determine
which ports should be forwarding and which should be blocking. If costs are equal, the STP reads
through BPDU until it finds a parameter that is not equal. The lower port ID becomes the
forwarding port, and the higher port ID is placed in a blocked state. As the BPDU prepares to leave
a port, it applies a port cost. The sum of all the port costs is the path cost. Spanning Tree looks
first at the path cost to decide which ports should forward and which should block. The port that

reports the lowest path cost is chosen to forward.

Reference: Building Cisco Multilayer Switched Networks (Ciscopress) page 155



Q21. Which process plays a major role in the creation of the CEF adjacency table?

A. Address Resolution Protocol (ARP)
B. PDU header rewrite
C. NetFlow switching
D. Hello packet exchange

Answer: A

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Explanation: The next step in processing a packet in a Layer 3 device is to determine the Payer 2
information needed to switch the packet to the next hop. This Layer 2 information is generally
contained in the ARP cache table. Cisco Express Forwarding creates a adjacency table to prepend
the layer 2 information.

Reference: Building Cisco Multilayer Switched Networks (Ciscopress) page 412



Q22. In the hardware address 0000.0c07.ac0a what does 07.ac represent?

A. Vendor code
B. HSRP group number
C. HSRP router number
D. HSRP well-known physical MAC address
E. HSRP well-known virtual MAC address

Answer: E

Explanation: HSRP code (HSRP well-known virtual MAC address) – The fact that the MAC address is
for an HSRP virtual router is indicated in the next two bytes of the address. The HSRP code is
always 07.ac.

Reference: Building Cisco Multilayer Switched Networks (Ciscopress) page 268



Q23. IEEE 802.1w RSTP defines which port states?

A. Listening, Learning, Forwarding, Blocking, Disabled
B. Learning, Forwarding, Discarding
C. Learning, Active, Block
D. Listening, Forwarding, Active, Blocking

Answer: B

Explanation: There are only three port states left in RSTP, corresponding to the three possible
operational states. The 802.1d states disabled, blocking, and listening have been merged into a
unique 802.1w discarding state.

Reference:

/>l#subtopic1a



Q24. When a VLAN port configured as a trunk receives an untagged frame, what will happen?

A. The frame will be dropped.
B. The frame will cause an error message to be sent.
C. The frame will be processed as a native VLAN frame.
D. The frame will be tagged, then processed as a native VLAN frame.