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QUESTION 131
Which kind of management can be performed from the console port of a Cisco 6500 switch?
A. Physical management of the switch.
B. Logical management of the switch.
C. In-band management of the switch.
D. Out-of-band management of the switch.

Correct Answer: D Section: (none) Explanation Explanation/Reference:
Explanation:
When you configure a switch or a router from the console, it is considered ‘out of band’ because you don’t
get in there from any of the paths that the network device is a part of.
Modems are often attached to the console port, providing for remote out of band management of the
device.

QUESTION 132
A VTP domain named Certkiller has six active VLANs. Without notice, all VLANs except VLAN1 fail. Just prior to the failure, Switch Certkiller 2 was added to the network.
Which three issues on Switch Certkiller 2 could be the cause? Select three.
A. Switch Certkiller 2 is configured for only VLAN1.
B. Switch Certkiller 2 is a VTP server in a different domain.
C. Switch Certkiller 2 is a VTP server in the Certkiller domain.
D. Switch Certkiller 2 is not a VTP domain.
E. Switch Certkiller 2 has a lower VTP configuration revision number than the current VTP revision.
F. Switch Certkiller 2 has a higher VTP configuration revision number than the current VTP revision.

Correct Answer: ACF Section: (none) Explanation
Explanation/Reference:
Explanation: A VTP server in a given domain with the highest revision number will overwrite the VTP configuration of all other switch in the same VTP domain. Cisco best practices advises one to configure the correct VTP domain, VTP password, VTP mode, (server, client, transparent), and VTP revision number before adding any new switch to a network. The default VTP mode is server. A network can have more than one VTP domain. Each VTP domain has it own server(s) that do not influence clients in other VTP domains.
QUESTION 133
You work as a network Technician at Certkiller .com. A new workstation has consistently been unable to obtain an IP address from the DHCP server when the workstation boots. Older workstations function normally, and the new workstation obtains an address when manually forced to renew its address.
What should be configured on the switch to allow the workstation to obtain an IP address at boot?
A. UplinkFast on the switch port connected to the server
B. BackboneFast on the switch port connected to the server
C. PortFast on the switch port connected to the workstation
D. trunking on the switch

Correct Answer: C Section: (none) Explanation
Explanation/Reference:
Explanation: Spanning tree PortFast is a Catalyst feature that causes a switch or trunk port to enter the spanning tree Forwarding state immediately, bypassing the Listening and Learning states. IOS-based switches only use PortFast on access ports connected to end stations. When a device is connected to a port, the port normally enters the spanning tree Listening state. When the Forward Delay timer expires, the port enters the Learning state. When the Forward Delay timer expires a second time, the port is transitioned to the Forwarding or Blocking state. When PortFast is enabled on a switch or trunk port, the port is immediately transitioned to the Forwarding state. As soon as the switch detects the link, the port is transitioned to the Forwarding state (less than 2 seconds after the cable is plugged in).
QUESTION 134
A topology change has occurred in the Certkiller network causing an STP change.
Which two statements concerning STP state changes are true? (Select two)
A. If a forwarding port receives an inferior BPDU, it will transition to listening.
B. Upon bootup, a port transitions from blocking to listening because it assumes itself as root.
C. Upon bootup, a port transitions from listening to forwarding because it assumes itself as root.
D. Upon bootup, a port transitions from blocking to forwarding because it assumes itself as root.
E. If a blocked port receives no BPDUs by the max_age time limit, it will transition to listening.
F. If a forwarding port receives no BPDUs by the max_age time limit, it will transition to listening.

Correct Answer: BE Section: (none) Explanation
Explanation/Reference:
Explanation: As a first step in the STP process, the switches need to elect a single Root Bridge by looking for the bridge with the lowest BID. This process of selecting the bridge with the lowest BID is sometimes called the “root war.” A BID is an 8-byte identifier that is composed of two subfields, the Bridge Priority and a MAC address. The process of how to configure a switch to become the Root Bridge will be examined in the following topics. Normally, the default settings should not be allowed to determine the location of the Root Bridge. How did the bridges learn that Cat-A has the lowest BID? This is accomplished through the exchange of BPDUs. As discussed earlier, BPDUs are special frames that bridges use to exchange spanning tree information with each other. By default, BPDUs are sent out every two seconds. BPDUs propagate between bridges, which includes switches and all routers configured for bridging. BPDUs do not carry end-user traffic.
QUESTION 135
Switch CK1 is configured with the RSTP feature. What will occur when a non edge switch port that is configured for Rapid Spanning Tree does not receive a BPDU from its neighbor for three consecutive hello time intervals?
A. RSTP information is automatically aged out.
B. The port sends a TCN to the root bridge.
C. The port moves to listening state.
D. The port becomes a normal spanning tree port.
E. None of the above

Correct Answer: A Section: (none) Explanation
Explanation/Reference:
Explanation: The IEEE 802.1D Spanning Tree Protocol was designed to keep a switched or bridged network loop free, with adjustments made to the network topology dynamically. A topology change typically takes 30 seconds, where a port moves from the Blocking state to the Forwarding state after two intervals of the Forward Delay timer. As technology has improved, 30 seconds has become an unbearable length of time to wait for a production network to failover or “heal” itself during a problem. The IEEE 802.1w standard was developed to take 802.1D’s principle concepts and make the resulting convergence much faster. This is also known as the Rapid Spanning Tree Protocol (RSTP). RSTP defines how switches must interact with each other to keep the network topology loop free, in a very efficient manner. Like 802.1D, RSTP’s basic functionality can be applied as a single or multiple instances. This can be done as the IEEE 802.1s Multiple Spanning Tree (MST). BPDUs are sent out every switch port at Hello Time intervals, regardless of whether BPDUs are received from the Root. In this way, any switch anywhere in the network can play an active role in maintaining the topology. Switches can also expect to receive regular BPDUs from their neighbors. When three BPDUs are missed in a row, that neighbor is presumed to be down, and all information related to the port leading to the neighbor is immediately aged out. This means that a switch can detect a neighbor failure in three Hello intervals (default 6 seconds), versus the Max Age Timer interval (default 20 seconds) for 802.1D.
QUESTION 136
You have been tasked with optimizing the STP operation in the Certkiller switched LAN. Which two statements about the various implementations of STP are true? (Select two)
A. Common Spanning Tree maintains a separate spanning-tree instance for each VLAN configured in the network.
B. Per-VLAN Spanning Tree (PVST) supports 802.1Q trunking.
C. Rapid Spanning Tree Protocol (RSTP) includes features equivalent to Cisco PortFast, UplinkFast, and BackboneFast for faster network reconvergence.
D. Multiple Spanning Tree (MST) assumes one spanning-tree instance for the entire Layer 2 network, regardless of the multiple number of VLANs.
E. The Spanning Tree Protocol (STP) is an evolution of the IEEE 802.1w standard.
F. Per-VLAN Spanning Tree Plus(PVST+) is an enhancement to 802.1Q specification and is supported only on Cisco devices.

Correct Answer: CF Section: (none) Explanation
Explanation/Reference:
Explanation: In 802.1D, BPDUs basically originate from the Root Bridge and are relayed by all switches down through the tree. It is because of this propagation of BPDUs that 802.1D convergence must wait for steady-state conditions before proceeding. RSTP uses the 802.1D BPDU format for backward-compatibility. However, some previously unused bits in the Message Type field are used. The sending switch port identifies itself by its RSTP role and state. The BPDU version is also set to 2, to distinguish RSTP BPDUs from 802.1D BPDUs. Also, RSTP uses an interactive process so that two neighboring switches can negotiate state changes. Some BPDU bits are used to flag messages during this negotiation. BPDUs are sent out every switch port at Hello Time intervals, regardless of whether BPDUs are received from the Root. In this way, any switch anywhere in the network can play an active role in maintaining the topology. Switches can also expect to receive regular BPDUs from their neighbors. When three BPDUs are missed in a row, that neighbor is presumed to be down, and all information related to the port leading to the neighbor is immediately aged out. This means that a switch can detect a neighbor failure in three Hello intervals (default 6 seconds), versus the Max Age Timer interval (default 20 seconds) for 802.1D. Because RSTP distinguishes its BPDUs from 802.1D BPDUs, it can coexist with switches still using 802.1D. Each port attempts to operate according to the STP BPDU that is received. For example, when an 802.1D BPDU (version 0) is received on a port, that port begins to operate according to the 802.1D rules. However, each port has a measure that locks the protocol in use for the duration of the migration delay timer. This keeps the protocol type from flapping or toggling during a protocol migration. After the timer expires, the port is free to change protocols if needed.
QUESTION 137
You have noticed a large number of topology changes in the Certkiller Rapid Spanning Tree Protocol network. Which statement is true about RSTP topology changes?
A. Only nonedge ports moving to the blocking state generate a TC BPDU.
B. Any loss of connectivity generates a TC BPDU.
C. Any change in the state of the port generates a TC BPDU.
D. Only nonedge ports moving to the forwarding state generate a TC BPDU.
E. If either an edge port or a nonedge port moves to a block state, then a TC BPDU is generated.
F. None of the above.

Correct Answer: D Section: (none) Explanation
Explanation/Reference:
Explanation: The IEEE 802.1D Spanning Tree Protocol was designed to keep a switched or bridged network loop free, with adjustments made to the network topology dynamically. A topology change typically takes 30 seconds, where a port moves from the Blocking state to the Forwarding state after two intervals of the Forward Delay timer. As technology has improved, 30 seconds has become an unbearable length of time to wait for a production network to failover or “heal” itself during a problem. Topology Changes and RSTP Recall that when an 802.1D switch detects a port state change (either up or down), it signals the Root Bridge by sending topology change notification (TCN) BPDUs. The Root Bridge must then signal a topology change by sending out a TCN message that is relayed to all switches in the STP domain. RSTP detects a topology change only when a nonedge port transitions to the Forwarding state. This might seem odd because a link failure is not used as a trigger. RSTP uses all of its rapid convergence mechanisms to prevent bridging loops from forming. Therefore, topology changes are detected only so that bridging tables can be updated and corrected as hosts appear first on a failed port and then on a different functioning port. When a topology change is detected, a switch must propagate news of the change to other switches in the network so they can correct their bridging tables, too. This process is similar to the convergence and synchronization mechanism-topology change (TC) messages propagate through the network in an ever-expanding wave.
QUESTION 138
You want to make a number of Certkiller switches part of the same Spanning Tree.
What must be the same to make multiple switches part of the same Multiple Spanning Tree (MST)?
A. VLAN instance mapping and revision number
B. VLAN instance mapping and member list
C. VLAN instance mapping, revision number, member list, and timers
D. VLAN instance mapping, revision number, and member list
E. None of the above

Correct Answer: D Section: (none) Explanation
Explanation/Reference:
Explanation:
By default, a switch operates in the Per VLAN Spanning Tree Plus (PVST+) mode using traditional 802.1D
STP. Therefore, RSTP cannot be used until a different Spanning Tree mode (MST or RPVST+) is enabled.
Remember that RSTP is just the underlying mechanism that a Spanning Tree mode can use to detect
topology changes and converge a network into a loop-free topology.
MST is built on the concept of mapping one or more VLANs to a single STP instance.
Multiple instances of STP can be used (hence the name MST), with each instance supporting a different
group of VLANs.
Each could be tuned to result in a different topology, so that Instance 1 would forward on

the left uplink, while Instance 2 would forward on the right uplink. Therefore, VLAN A would be mapped to
Instance 1, and VLAN B to Instance 2.
In most networks, a single MST region is sufficient, although you can configure more than one region.
Within the region, all switches must run the instance of MST that is defined by the following attributes:

1.
MST configuration name (32 characters)
2.
MST configuration revision number (0 to 65535)
3.
MST instance-to-VLAN mapping table (4096 entries)
Reference:
http://www.cisco.com/en/US/tech/ CK3 89/ CK6 21/technologies_white_paper09186a0080094cfc.shtml

QUESTION 139
An access layer switch in the Certkiller network has just received a BPDU from a neighboring device. What two things will occur when an edge port receives a BPDU? (Select two)
A. The port immediately transitions to the err-disable state.
B. The port becomes a normal STP switch port.
C. The switch generates a Topology Change Notification (TCN) BPDU.
D. The port immediately transitions to the Forwarding state.

Correct Answer: BC Section: (none) Explanation
Explanation/Reference:
Explanation: Recall that when an 802.1D switch detects a port state change (either up or down), it signals the Root Bridge by sending topology change notification (TCN) BPDUs. The Root Bridge must then signal a topology change by sending out a TCN message that is relayed to all switches in the STP domain. RSTP detects a topology change only when a nonedge port transitions to the Forwarding state. This might seem odd because a link failure is not used as a trigger. RSTP uses all of its rapid convergence mechanisms to prevent bridging loops from forming. Therefore, topology changes are detected only so that bridging tables can be updated and corrected as hosts appear first on a failed port and then on a different functioning port.
QUESTION 140
Please refer to the Certkiller Switched LAN shown below:
Given the diagram shown above and assuming that STP is enabled on all switch devices, which two statements are true? (Select two.)
A. P2/2 will be elected the nondesignated port.
B. P3/2 will be elected the nondesignated port.
C. P3/1 will be elected the nondesignated port.
D. Certkiller 2 will be elected the root bridge.
E. Certkiller 1 will be elected the root bridge.
F. Certkiller 3 will be elected the root bridge.

Correct Answer: CE Section: (none) Explanation
Explanation/Reference:
Explanation:
The Root Bridge in a network using RSTP is elected just as with 802.1D-by the lowest Bridge ID. After all
switches agree on the identity of the Root, the following port roles are determined:

1.
RootPort-The one switch port on each switch that has the best root path cost to the Root. This is identical to 802.1D. (By definition, the Root Bridge has no Root Ports.)

2.
Designated Port-The switch port on a network segment that has the best root path cost to the Root.

3.
AlternatePort-A port that has an alternate path to the Root, different than the path the Root Port takes. This path is less desirable than that of the Root Port. (An example of this is an accesslayer switch with two uplink ports; one becomes the Root Port, the other is an Alternate Port.)

4.
BackupPort-A port that provides a redundant (but less desirable) connection to a segment where another switch port already connects. If that common segment is lost, the switch might or might not have a path back to the Root.
QUESTION 141
The Certkiller switches have been implemented with the extended ID system feature.
Which two statements are true when the extended system ID feature is enabled? (Select two)
A. The BID is made up of the bridge priority (four bits), the system ID (12 bits), and a bridge MAC address (48 bits).
B. The BID is made up of the system ID (six bytes) and bridge priority value (two bytes).
C. The BID is made up of the bridge priority value(two bytes) and bridge MAC address (six bytes).
D. The system ID value is a unique MAC address allocated from a pool of MAC addresses assigned to the switch or module.
E. The system ID value is a hex number used to measure the preference of a bridge in the spanning-tree algorithm.
F. The system ID value is the VLAN ID (VID).

Correct Answer: AF Section: (none) Explanation
Explanation/Reference:
Explanation: Extended System ID feature (also known as MAC address allocation and reduction)is used for PVST+ in the case that there are too many VLANs and notenough instances to map to. It uses the System ID (VLAN ID), Bridge Priority, and MAC Address as shown below.(refer to attachment). The VLAN ID is used as the System ID. These means that when setting Bridge priority, since you can only use the 4 highest bits, you must usemultiples of 4096. Reference: “BCMSN fourth edition” by Richard Froom page 237-8
QUESTION 142
What will occur when a non-edge switch port that is configured for Rapid Spanning Tree does not receive a BPDU from its neighbor for three consecutive hello time intervals?
A. RSTP information is automatically aged out.
B. The port sends a TCN to the root bridge.
C. The port moves to listening state.
D. The port becomes a normal spanning tree port.

Correct Answer: A Section: (none) Explanation
Explanation/Reference:
Explanation:
The IEEE 802.1D Spanning Tree Protocol was designed to keep a switched or bridged

network loop free, with adjustments made to the network topology dynamically. A topology change typically
takes 30 seconds, where a port moves from the Blocking state to the Forwarding state after two intervals of
the Forward Delay timer. As technology has improved, 30 seconds has become an unbearable length of
time to wait for a production network to failover or “heal” itself during a problem.
The IEEE 802.1w standard was developed to take 802.1D’s principle concepts and make the resulting
convergence much faster. This is also known as the Rapid Spanning Tree Protocol (RSTP).
RSTP defines how switches must interact with each other to keep the network topology loop free, in a very
efficient manner. Like 802.1D, RSTP’s basic functionality can be applied as a single or multiple instances.
This can be done as the IEEE 802.1s Multiple Spanning Tree (MST), covered in this chapter, and also as
the Cisco-proprietary, Rapid Per-VLAN Spanning Tree Protocol (RPVST+). RSTP operates consistently in
each, but replicating RSTP as multiple instances requires different approaches.
In 802.1D, BPDUs basically originate from the Root Bridge and are relayed by all switches down through
the tree. It is because of this propagation of BPDUs that 802.1D convergence must wait for steady-state
conditions before proceeding.
RSTP uses the 802.1D BPDU format for backward-compatibility. However, some previously unused bits in
the Message Type field are used. The sending switch port identifies itself by its RSTP role and state. The
BPDU version is also set to 2, to distinguish RSTP BPDUs from 802.1D BPDUs.
Also, RSTP uses an interactive process so that two neighboring switches can negotiate state changes.
Some BPDU bits are used to flag messages during this negotiation.
BPDUs are sent out every switch port at Hello Time intervals, regardless of whether BPDUs are received
from the Root. In this way, any switch anywhere in the network can play an active role in maintaining the
topology. Switches can also expect to receive regular BPDUs from their neighbors.
When three BPDUs are missed in a row, that neighbor is presumed to be down, and all information related
to the port leading to the neighbor is immediately aged out. This means that a switch can detect a neighbor
failure in three Hello intervals (default 6 seconds), versus the Max Age Timer interval (default 20 seconds)
for 802.1D.
Because RSTP distinguishes its BPDUs from 802.1D BPDUs, it can coexist with switches still using

802.1D. Each port attempts to operate according to the STP BPDU that is received. For example, when an 802.1D BPDU (version 0) is received on a port, that port begins to operate according to the 802.1D rules. However, each port has a measure that locks the protocol in use for the duration of the migration delay timer. This keeps the protocol type from flapping or toggling during a protocol migration. After the timer expires, the port is free to change protocols if needed.
QUESTION 143
The Certkiller network administrator is fine tuning the STP parameters on the Catalyst switches. In which states does the Spanning Tree protocol (STP) get affected by the forward delay parameter? (Select two)
A. Forwarding
B. Listening
C. Blocking
D. Disabled
E. Learning

Correct Answer: BE Section: (none) Explanation
Explanation/Reference:
Explanation: The following states utilize information from the forward delay timer: Listen – The switch listens for a period of time called the fwd delay (forward delay) Learn – The switch learns for a period of time called the fwd delay (forward delay) Reference: Building Cisco Multilayer Switched Networks (Cisco Press) page 139
QUESTION 144
If two paths to a root switch share the exact same path cost, what information will spanning tree use to determine the root port?
A. The lowest time to receive BPDUs.
B. The lowest Port ID.
C. The lowest sender bridge ID.
D. The highest MAC address on the receiving port.
E. None of the above.

Correct Answer: C Section: (none) Explanation
Explanation/Reference:
Explanation: A Root Bridge is chosen based on the results of the BPDU process between the switches. Initially, every switch considers itself the Root Bridge! When a switch first powers up on the network, it sends out a BPDU with its own BID as the Root BID. When the other switches receive the BPDU, they compare the BID to the one they already have stored as the Root BID. If the new Root BID has a lower value, they replace the saved one. But if the saved Root BID is lower, a BPDU is sent to the new switch with this BID as the Root BID. When the new switch receives the BPDU, it realizes that it is not the Root Bridge and replaces the Root BID in its table with the one it just received. The result is that the switch that has the lowest BID is elected by the other switches as the Root Bridge. Based on the location of the Root Bridge, the other switches determine which of their ports has the lowest path cost to the Root Bridge. These ports are called Root Ports and each switch (other than the current Root Bridge) must have one. The switches determine who will have Designated Ports. A Designated Port is the connection used to send and receive packets on a specific segment. By having only one Designated Port per segment, all looping issues are resolved! Designated Ports are selected based on the lowest path cost to the Root Bridge for a segment. Since the Root Bridge will have a path cost of “0”, any ports on it that are connected to segments will become Designated Ports. For the other switches, the path cost is compared for a given segment. If one port is determined to have a lower path cost, then it becomes the Designated Port for that segment. If two or more ports have the same path cost, then the switch with the lowest BID is chosen.
QUESTION 145
In the Certkiller STP environment, what is true regarding a topology change?
A. The default aging time for MAC address entries will be reduced for a period of the max_age timer plus the forward_delay interval.
B. All ports will transition temporarily to the learning state for a period equal to the forward_delay interval.
C. All ports will temporarily transition to the learning state for a period equal to the max_age timer plus the forward_delay interval.
D. The default hello_timer for configuration BDPUs will be reduced for the period of the max_age timer.
E. None of the above

Correct Answer: A Section: (none) Explanation
Explanation/Reference:
Explanation: Purpose of the Topology Change Mechanism Learning from the frames it receives, a bridge creates a table that associates to a port the Media Access Control (MAC) addresses of the hosts that can be reached through this port. This table is used to forward frames directly to their destination port. Therefore, flooding is avoided. Default aging time for this table is 300 seconds (five minutes). Only after a host has been silent for five minutes, its entry disappears from the table of the bridge. Here is an example that shows why you could want this aging to be faster: In this network, assume that bridge B1 is blocking its link to B4. A and B are two stations that have an established connection. Traffic from A to B goes to B1, B2, B3, and then B4. The scheme shows the MAC addresses table learned by the four bridges in this situation:
Now, assume the link between B2 and B3 fails. Communication between A and B is interrupted at least until B1 puts its port to B4 in forwarding mode (a maximum of 50 seconds with default parameters). However, when A wants to send a frame to B, B1 still has an entry that leads to B2 and the packet is sent to a black hole. The same applies
when B wants to reach A. Communication is lost for five minutes, until the entries for A and B MAC addresses age out.
The forwarding databases implemented by bridges are very efficient in a stable network. However, there are many situations where the five minute aging time is a problem after the topology of the network has changed. The topology change mechanism is a workaround for that kind of problem. As soon as a bridge detects a change in the topology of the network (a link that goes down or goes to forwarding), it advertises the event to the whole bridged network. Every bridge is then notified and reduces the aging time to forward_delay (15 seconds by default) for a certain period of time (max_age + forward_delay). It is more beneficial to reduce the aging time instead of clearing the table because currently active hosts, that effectively transmit traffic, are not cleared from the table. In this example, as soon as bridge B2 or B3 detects the link going down, it sends topology change notifications. All bridges become aware of the event and reduce their aging time to 15 seconds. As B1 does not receive any packet from B on its port leading to B2 in fifteen seconds, it ages out the entry for B on this port. The same happens to the entry for A on the port that leads to B3 on B4. Later when the link between B1 and B4 goes to forwarding, traffic is immediately flooded and re-learned on this link. Reference: http://www.cisco.com/en/US/tech/ CK3 89/ CK6 21/ technologies_tech_note09186a0080094797.shtml#topic1
QUESTION 146
Multiple Certkiller switches are connected together, forming a loop in the network to provide redundancy. Which of the following technologies provides loop avoidance?
A. VTP
B. MLS-RP
C. MLS-SE
D. VTP Pruning
E. STP
F. STP Trunking
G. None of the above

Correct Answer: E Section: (none) Explanation
Explanation/Reference:
Explanation: Spanning-Tree Protocol (STP) is a Layer 2 protocol designed to run on bridges and switches. The specification for STP is defined in IEEE 802.1d. The main purpose of STP is to ensure that you do not run into a loop situation when you have redundant paths in your network. STP detects/disables network loops and provides backup links between switches or bridges. It allows the device to interact with other STP compliant devices in your network to ensure that only one path exists between any two stations on the network. Reference: http://www.zyxel.com/support/supportnote/ves1012/app/stp.htm
QUESTION 147
Before a port can participate in the STP process the ports have to change. In which sequence do the STP port states change through?
A. Initial, Learning, Updating, and Active
B. Blocking, Listening, Updating, and Active
C. Initial, Learning, Updating, and Forwarding
D. Blocking, Listening, Learning, and Forwarding

Correct Answer: D Section: (none) Explanation
Explanation/Reference:
Explanation:
The correct order is: blocking state (not participating), listening, learning (prepares to participate), and
Forwarding.
Note: STP states:

1.
Blocking-The Layer2 LAN port does not participate in frame forwarding

2.
Listening-First transitional state after the blocking state when STP determines that the Layer2 LAN port should participate in frame forwarding

3.
Learning-The Layer2 LAN port prepares to participate in frame forwarding

4.
Forwarding-The Layer2 LAN port forwards frames

5.
Disabled-The Layer2 LAN port does not participate in STP and is not forwarding frames.
QUESTION 148
In order for STP to run successfully on the Certkiller network, what standard the bridges and switches have to comply with?
A. 802.1c
B. 802.1e
C. 802.1x
D. 802.1f
E. 802.1d
F. 802.11
Correct Answer: E Section: (none) Explanation

Explanation/Reference:
Explanation: According to the online documentation provided by Cisco: STP runs on bridges and switches that are 802.1d-compliant. There are different flavors of STP, with IEEE 802.1d being the most popular and widely implemented. STP is implemented on bridges and switches in order to prevent loops in the network. Use it in situations where you want redundant links, but not loops. Redundant links are important as backups in case of failover in a network. If your primary fails, the backup links are activated so that users can continue using the network. Without STP on the bridges and switches, such a situation could result in a loop.
QUESTION 149
Switches CK1 and CK2 are exchanging Bridge Protocol Data Unit (BPDU) information. Which of the following can result from a BPDU exchange? (Select all that apply)
A. One switch is elected as the root switch.
B. Ports included in the spanning tree are selected.
C. The shortest distance to the root switch is calculated
D. A designated bridge for each LAN segment is selected.
E. A root port is selected.

Correct Answer: ABCDE Section: (none) Explanation
Explanation/Reference:
Explanation:
A BPDU exchange between devices results in the following: One switch is elected as the root switch.
The shortest distance to the root switch is calculated for each switch based on the path cost.
A designated bridge for each LAN segment is selected. This is the switch closest to the root bridge through
which frames are forwarded to the root.
A root port is selected. This is the port providing the best path from the bridge to the root bridge.
Ports included in the spanning tree are selected.

QUESTION 150
What determines the default spanning tree port path cost of STP devices within the Certkiller network?
A. The server speed settings
B. The available bandwidth.
C. The media speed of an interface.
D. The stored IOS settings
E. The interface number

Correct Answer: C Section: (none) Explanation
Explanation/Reference:
Explanation:
The spanning tree port path cost default value is derived from the media speed of an interface. In the event
of a loop, spanning tree considers port cost when selecting an interface to put into the forwarding state.
You can assign lower cost values to interfaces that you want spanning tree to select first and higher cost
values to interfaces that you want spanning tree to select last. If all interfaces have the same cost value,
spanning tree puts the interface with the lowest interface number in the forwarding state and blocks other
interfaces. The possible cost range is 1 through 200000000 (the default is media specific).

QUESTION 151
Switch CK1 is a non-root switch in the Certkiller network. By what method 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. The port receives an inferior BPDU from a neighboring switch on a shard LAN segment.
C. It chooses the port with the highest cumulative Root Path Cost to the Root Bridge.
D. The port receives a BPDU announcing a higher Root Path Cost from a neighboring switch on a shared LAN segment.
E. None of the above.

Correct Answer: A Section: (none) Explanation
Explanation/Reference:
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 (Cisco Press) page 155
QUESTION 152
What is the default transition time for a switch in the Certkiller switched LAN to move from blocking to forwarding state in the Spanning-Tree protocol?
A. 5 seconds
B. 50 seconds
C. 60 seconds
D. 90 seconds
E. 120 seconds

Correct Answer: B Section: (none) Explanation
Explanation/Reference:
Explanation: The default STP timers are shown below: From blocking to listening 20 seconds From listening to learning 15 seconds From learning to forwarding 15 seconds From blocking to forwarding state 50 seconds Reference: Building Cisco Multilayer Switched Networks (Cisco Press) page 141
QUESTION 153
DRAG DROP Drag the Spanning Tree Protocol state in the options column on the left to the matching definition column on the right.
Explanation: After the bridges have determined which ports are Root Ports, Designated Ports, and non-Designated Ports, STP is ready to create a loop-free topology. To do this, STP configures Root Ports and Designated Ports to forward traffic. STP sets non-Designated Ports to block traffic. Although Forwarding and Blocking are the only two states commonly seen in a stable network, there are actually five STP states. This list can be viewed hierarchically in that bridge ports start at the Blocking state and work their way up to the Forwarding state. The Disabled state is the administratively shutdown STP state. It is not part of the
normal STP port processing. After the switch is initialized, ports start in the Blocking state. The Blocking
state is the STP state in which a bridge listens for BPDUs.
A port in the Blocking state does the following:

1.
Discards frames received from the attached segment or internally forwarded through switching

2.
Receives BPDUs and directs them to the system module

3.
Has no address database

4.
Does not transmit BPDUs received from the system module

5.
Receives and responds to network management messages but does not transmit them If a bridge thinks it is the Root Bridge immediately after booting or in the absence of BPDUs for a certain period of time, the port transitions into the Listening state. The Listening state is the STP state in which no user data is being passed, but the port is sending and receiving BPDUs in an effort to determine the active topology. A port in the Listening state does the following:
1.
Discards frames received from the attached segment or frames switched from another port

2.
Has no address database

3.
Receives BPDUs and directs them to the system module

4.
Processes BPDUs received from the system module (Processing BPDUs is a separate action from receiving or transmitting BPDUs)

5.
Receives and responds to network management messages
It is during the Listening state that the three initial convergence steps take place – elect a Root Bridge, elect Root Ports, and elect Designated Ports. Ports that lose the Designated Port election become non-Designated Ports and drop back to the Blocking state. Ports that remain Designated Ports or Root Ports after 15 seconds – the default Forward Delay STP timer value – progress into the Learning state. The lifetime of the Learning state is also governed by the Forward Delay timer of 15 seconds, the default setting. The Learning state is the STP state in which the bridge is not passing user data frames but is building the bridging table and gathering information, such as the source VLANs of data frames. As the bridge receives a frame, it places the source MAC address and port into the bridging table. The Learning state reduces the amount of flooding required when data forwarding begins. A port in the Learning state does the following:
1.
Discards frames received from the attached segment
2.
Discards frames switched from another port for forwarding
3.
Incorporates station location into its address database
4.
Receives BPDUs and directs them to the system module
5.
Receives, processes, and transmits BPDUs received from the system module
6.
Receives and responds to network management messages
If a port is still a Designated Port or Root Port after the Forward Delay timer expires for the Learning state,
the port transitions into the Forwarding state. The Forwarding state is the STP state in which data traffic is
both sent and received on a port. It is the “last” STP state. At this stage, it finally starts forwarding user
data frames.
A port in the Forwarding state does the following:

1.
Forwards frames received from the attached segment
2.
Forwards frames switched from another port for forwarding
3.
Incorporates station location information into its address database
4.
Receives BPDUs and directs them to the system module
5.
Processes BPDUs received from the system module
6.
Receives and responds to network management messages

A.

B.

C.

D.
Correct Answer: Section: (none) Explanation
Explanation/Reference: QUESTION 154
Switch CK1 is participating in the Spanning Tree Protocol (STP). What is true about STP Path Cost on a particular port of CK1 ?
A. It is known only to the local switch where the port resides.
B. It can be modified to help determine Root Bridge selection.
C. Modifying it can cause TCN BPDU to be sent to the Root Bridge.
D. When increased, it can provide higher bandwidth to a connecting port.
E. None of the above

Correct Answer: A Section: (none) Explanation
Explanation/Reference:
Explanation:
With STP, first a root bridge is elected. Then, the shortest distance to the root bridge is calculated for each
switch based on the path cost. This calculation is done locally on each switch and the path cost for that
switch is only used on the local switch.

Incorrect
Answers:

B: Adjust the STP port priority, not the port path cost, can be done to influence the election of the root
bridge.

C: A bridge considers it a topology change only when one of the following occurs:

1.
When a port that was forwarding is going down (blocking for instance).
2.
When a port transitions to forwarding and the bridge has a designated port. (This
means that the bridge is not standalone.)
TCN BPDUs are only sent to other switches within the network if one of the above happens.

D: Simply adjusting the cost value of the port will not make the port faster or provide for additional
bandwidth throughput.

QUESTION 155
Study the exhibit below:
Switch Certkiller 2 Switch Certkiller 3 Bridge ID: 32768.00-00-00-00-00-01 Bridge ID: 32768.00-00-00-00-00-02 Given the network configuration above and assuming that STP is enabled, which port will be elected the non-designated port?
A. Port 1/1
B. Port 1/2
C. Port 2/1
D. Port 2/2
E. Port 3/1
F. Port 3/2

Correct Answer: B Section: (none) Explanation
Explanation/Reference:
Explanation:
For each VLAN, the switch with the highest bridge priority (the lowest numerical

priority value) is elected as the root bridge. If all switches are configured with the default priority value
(32,768), the switch with the lowest MAC address in the VLAN becomes the root bridge.
The spanning tree root bridge is the logical center of the spanning tree topology in a switched network. All
paths that are not required to reach the root bridge from anywhere in the switched network are placed in
spanning tree blocking mode.

A spanning tree uses the information provided by BPDUs to elect the root bridge and root port for the switched network, as well as the root port and designated port for each switched segment. In this example, since the priorities are set to the default, the switch with the lowest MAC address is used as the tie breaker. In this case, Certkiller 2 will become the root switch, which means that port 3/1 and 1/1 will become the root ports and must be in the forwarding state. That leaves the other port on switch Certkiller 1, port 1/2 as the non-designated port since this switch has the highest MAC address.
QUESTION 156
Switch CK1 is powered on for the first time in the Certkiller network. Upon initial bootup, which destination address does a CK1 use to send BPDUs?
A. A well-known STP multicast address.
B. The IP address of its default gateway.
C. The MAC addresses stored in the CAM table.
D. The MAC address of neighbors discovered via CDP
E. None of the above

Correct Answer: A Section: (none) Explanation
Explanation/Reference:
Explanation:
Bridge protocol data units (BPDUs) are used by the spanning tree algorithm to determine information about
the topology of the network BPDUs are used to send configuration messages using multicast frames.
When STP devices are first powered on, a well known multicast destination MAC address is used to send
the BPDU information.
Incorrect
Answers:

B: This would only send the BPDU information to the router. The other switches in the network that are participating in STP need the BPDU information, not the router.
C: When a switch is first powered up, the CAM table will be empty.
D: Since STP is standards based, it does not use any Cisco proprietary protocols such as CDP to perform any of its functions. This will ensure inter-operability with switches from other vendors.
QUESTION 157
Switch CK3 is calculating the root path cost to the Root Bridge, CK1 . What is true regarding the Root Path cost?
A. It is the Path Cost of a particular Root Port.
B. It is the cost sent from the Root Bridge to all non-root bridges.
C. This value is the cumulative cost of all the links leading to the Root Bridge.
D. This value is the cumulative cost of all links sent from the Designated Port of the Root Bridge.

Correct Answer: C Section: (none) Explanation
Explanation/Reference:
Explanation:
The first stage in the STP process is the calculation stage. During this stage, each bridge on the network
transmits BPDUs that allow the system to work out:

1.
The identity of the bridge that is to be the Root Bridge – the central reference point
from which the network is configured.
2.
The Root Path Costs for each bridge – that is, the cost of the paths from each
bridge to the Root Bridge. This value is found by adding up the cost of all of the links to the root bridge.
3.
The identity of the port on each bridge that is to be the Root Port – the one that is
connected to the Root Bridge using the most efficient path, that is, the one that has the lowest Root Path
Cost. Note that the Root Bridge does not have a Root Port.
4.
The identity of the bridge that is to be the Designated Bridge of each LAN segment -the one that has the lowest Root Path Cost from that segment. Note that if several bridges have the same

Root Path Cost, the one with the lowest Bridge Identifier becomes the Designated Bridge.
QUESTION 158
At which layer of the OSI model does the Spanning Tree Protocol (STP) operate at?
A. Layer 5
B. Layer 4
C. Layer 3
D. Layer 2
E. Layer 1

Correct Answer: D Section: (none) Explanation
Explanation/Reference:
Explanation:
Spanning-Tree Protocol (STP) is a Layer 2 (L2) protocol designed to run on bridges and switches. The
specification for STP is called 802.1d. The main purpose of STP is to ensure that you do not run into a loop
situation when you have redundant paths in your network. Loops are deadly to a network.

QUESTION 159
You want to influence the root switch election process within the Certkiller network.
When setting up STP in this network, which switch should you configure as the root switch?
A. The most centralized switch
B. The most secure switch
C. The most updated switch
D. The most powerful switch
E. The switch that has the longest uptime.

Correct Answer: A Section: (none) Explanation
Explanation/Reference:
Explanation:
Cisco recommends using the most centralized switch in the network as the root switch.
According to Cisco:
Before configuring STP, you need to select a switch to be the root of the spanning tree. It does not
necessarily have to be the most powerful switch; it should be the most centralized switch on the network.
All dataflow across the network will be from the perspective of this switch. It is also important that this
switch be the least disturbed switch in the network. The backbone switches are often selected for this
function, because they typically do not have end stations connected to them. They are also less likely to be
disturbed during moves and changes within the network.

QUESTION 160
Which of the following factors are NOT used to determine the stable active spanning tree topology of the switched Certkiller network?
A. The port identifier associated with each Layer 2 interface
B. The port identifier associated with each Layer 3 interface
C. The spanning tree path cost to the root bridge
D. The unique bridge ID
E. All of the above are used.
Correct Answer: B Section: (none) Explanation

Explanation/Reference:
Explanation: The Spanning Tree Protocol does not use layer 3 information to determine the overall topology. Layer 3 interfaces do not participate in STP, since spanning tree is a layer 2 technology. Incorrect Answers: A, C, D: The stable active spanning tree topology of a switched network is determined by the following: -The unique bridge ID (bridge priority and MAC address) associated with each VLAN on each switch -The spanning tree path cost to the root bridge -The port identifier (port priority and MAC address) associated with each Layer 2 interface
QUESTION 161
A failure has occurred in the Certkiller switched network, causing a loop. What causes bridging loops to occur in a LAN?
A. A failure in the route-switch module
B. A failure in the VLAN tunnel
C. A failure in the VTP trunk
D. A failure in the STA
E. None of the above

Correct Answer: D Section: (none) Explanation
Explanation/Reference:
Explanation: The primary function of the spanning-tree algorithm (STA) is to cut loops created by redundant links in bridged networks. The Spanning-Tree Protocol (STP) operates at Layer 2 of the OSI model and, by the means of bridge protocol data units (BPDUs) exchanged between bridges, elects the ports that will eventually forward or block traffic. This protocol can fail in some specific cases and troubleshooting the resulting situation can be very difficult, depending on the design of the network. We can even say that in this particular area, the most important part of the troubleshooting is done before the problem occurs. A failure in the STA generally leads to a bridging loop (not a spanning tree loop as you don’t need STP to have a loop). Most customers calling the TAC for spanning tree problems are suspecting a bug, but experience proves that it is seldom the case. Even if the software is at stake, a bridging loop in a STP environment necessarily comes from a port that should block, but that is forwarding traffic.
QUESTION 162
The bridge priority of switch CK1 is being manually configured. In the STP root selection process, what happens to the switch with the lowest priority in the network?
A. It is withdrawn from the election process.
B. It loses the root bridge election process.
C. It wins the root bridge election process.
D. None of the above. The bridge priority is not used to determine the root bridge.

Correct Answer: C Section: (none) Explanation
Explanation/Reference:
Explanation:
As the BPDU goes out through the network, each switch compares the BPDU it sent out to the one it
received from its neighbors. From this comparison, the switches come to an agreement as to who the root
switch is. The switch with the lowest priority in the network wins this election process.

QUESTION 163
If a layer 2 interface on switch CK1 uses the Spanning Tree Protocol (STP) which of the following states could it NOT possibly be in at any time?
A. Forwarding
B. Learning
C. Disabled
D. Blocking
E. Listening
F. None of the above

Correct Answer: F Section: (none) Explanation
Explanation/Reference:
Explanation: According to Cisco: Each Layer 2 interface on a switch using spanning tree exists in one of the following five states: Blocking-The Layer 2 interface does not participate in frame forwarding Listening-First transitional state after the blocking state when spanning tree determines that the Layer 2 interface should participate in frame forwarding Learning-The Layer 2 interface prepares to participate in frame forwarding Forwarding-The Layer 2 interface forwards frames Disabled-The Layer 2 interface does not participate in spanning tree and is not forwarding frames.
QUESTION 164
When a network engineer designs a switch topology, they assign higher priority values to interfaces that they want spanning tree to select first and lower priority values to interfaces that they want spanning tree to select last. However, if multiple interfaces have equal priority values, spanning tree puts the interface with the __________ interface number in the forwarding state.
A. Neutral
B. Highest
C. Lowest
D. Random
E. First

Correct Answer: C Section: (none) Explanation
Explanation/Reference:
Explanation: In the event of a loop, spanning tree considers port priority when selecting an interface to put into the forwarding state. You can assign higher priority values to interfaces that you want spanning tree to select first and lower priority values to interfaces that you want spanning tree to select last. If all interfaces have the same priority value, spanning tree puts the interface with the lowest interface number in the forwarding state and blocks other interfaces.
QUESTION 165
What is the default priority value assigned to a switch when STP is enabled?
A. 1
B. 255
C. 4096
D. 32,768
E. 65,536
Correct Answer: D Section: (none) Explanation

Explanation/Reference:
Explanation:
Each switch has a unique Bridge ID that identifies it to other switches. The Bridge ID is an 8-byte value
consisting of the following fields:

1. Bridge Priority (2 bytes)-The priority or weight of a switch in relation to all other switches. The priority field can have a value of 0 to 65,535 and defaults to 32,768 (or 0x8000) on every Catalyst switch.
QUESTION 166
DRAG DROP
As a Certkiller .com administrator you are required to drag the port states to their correct description.

Explanation: After the bridges have determined which ports are Root Ports, Designated Ports, and non-Designated Ports, STP is ready to create a loop-free topology. To do this, STP configures Root Ports and Designated Ports to forward traffic. STP sets non-Designated Ports to block traffic. Although Forwarding and Blocking are the only two states commonly seen in a stable network, there are actually five STP states. This list can be viewed hierarchically in that bridge ports start at the Blocking state and work their way up to the Forwarding state. The Disabled state is the administratively shutdown STP state. It is not part of the normal STP port processing. After the switch is initialized, ports start in the Blocking state. The Blocking state is the STP state in which a bridge listens for BPDUs. A port in the Blocking state does the following:
1.
Discards frames received from the attached segment or internally forwarded through switching

2.
Receives BPDUs and directs them to the system module

3.
Has no address database

4.
Does not transmit BPDUs received from the system module

5.
Receives and responds to network management messages but does not transmit them If a bridge thinks it is the Root Bridge immediately after booting or in the absence of BPDUs for a certain period of time, the port transitions into the Listening state. The Listening state is the STP state in which no user data is being passed, but the port is sending and receiving BPDUs in an effort to determine the active topology. A port in the Listening state does the following:
1.
Discards frames received from the attached segment or frames switched from another port

2.
Has no address database

3.
Receives BPDUs and directs them to the system module

4.
Processes BPDUs received from the system module (Processing BPDUs is a separate action from receiving or transmitting BPDUs)

5.
Receives and responds to network management messages It is during the Listening state that the three initial convergence steps take place – elect a
Root Bridge, elect Root Ports, and elect Designated Ports. Ports that lose the Designated Port election become non-Designated Ports and drop back to the Blocking state. Ports that remain Designated Ports or Root Ports after 15 seconds – the default Forward Delay STP timer value – progress into the Learning state. The lifetime of the Learning state is also governed by the Forward Delay timer of 15 seconds, the default setting. The Learning state is the STP state in which the bridge is not passing user data frames but is building the bridging table and gathering information, such as the source VLANs of data frames. As the bridge receives a frame, it places the source MAC address and port into the bridging table. The Learning state reduces the amount of flooding required when data forwarding begins. A port in the Learning state does the following:
1.
Discards frames received from the attached segment

2.
Discards frames switched from another port for forwarding

3.
Incorporates station location into its address database

4.
Receives BPDUs and directs them to the system module

5.
Receives, processes, and transmits BPDUs received from the system module

6.
Receives and responds to network management messages
If a port is still a Designated Port or Root Port after the Forward Delay timer expires for the Learning state,
the port transitions into the Forwarding state. The Forwarding state is the STP state in which data traffic is
both sent and received on a port. It is the “last” STP state. At this stage, it finally starts forwarding user
data frames.
A port in the Forwarding state does the following:

1.
Forwards frames received from the attached segment
2.
Forwards frames switched from another port for forwarding
3.
Incorporates station location information into its address database
4.
Receives BPDUs and directs them to the system module
5.
Processes BPDUs received from the system module
6.
Receives and responds to network management messages

A.

B.

C.

D.
Correct Answer: Section: (none) Explanation
Explanation/Reference:
QUESTION 167
What is the purpose of MST, according to the IEEE 802.1s standard?
A. It is the spanning-tree implementation used by non-Cisco 802.1Q switches.
B. It runs a separate instance of STP for each VLAN.
C. It allows a VLAN bridge to use multiple spanning trees to prevent Layer 2 loops.
D. It creates a single loop-tree structure that spans the entire Layer 2 network.

Correct Answer: C Section: (none) Explanation
Explanation/Reference:
Explanation: IEEE 802.1s MST Overview MST allows you to build multiple spanning trees over trunks. You can group and associate VLANs to spanning tree instances. Each instance can have a topology independent of other spanning tree instances. This new architecture provides multiple forwarding paths for data traffic and enables load balancing. Network fault tolerance is improved because a failure in one instance (forwarding path) does not affect other
instances (forwarding paths). In large networks, you can more easily administer the network and use redundant paths by locating different VLAN and spanning tree instance assignments in different parts of the network. A spanningtree instance can exist only on bridges that have compatible VLAN instance assignments. You must configure a set of bridges with the same MST configuration information, which allows them to participate in a specific set of spanning tree instances. Interconnected bridges that have the same MST configuration are referred to as an MST region. Reference: http://www.cisco.com/en/US/products/hw/switches/ps708/ products_configuration_guide_chapter09186a008007 e
QUESTION 168
You work as a network technician at Certkiller .com. Your boss, Mrs. Certkiller, is interested in the Spanning Tree Protocol timers. What can you tell her regarding the default STP timers? (Select three)
A. The hello time is 5 seconds.
B. The forward delay is 10 seconds.
C. The hello time is 2 seconds.
D. The forward delay is 15 seconds
E. The max_age timer is 15 seconds.
F. The hello time is 10 seconds.
G. The max_age timer is 20 seconds.
H. The forward delay is 20 seconds.
I. The max_age timer is 30 seconds.

Correct Answer: CDG Section: (none) Explanation
Explanation/Reference:
Explanation:
The STP timers are:

1.
hello-The hello time is the time between each bridge protocol data unit (BPDU) that is
sent on a port. This time is equal to 2 seconds (sec) by default, but you can tune the time to be between 1
and 10 sec.
2.
forward delay-The forward delay is the time that is spent in the listening and learning
state. This time is equal to 15 sec by default, but you can tune the time to be between 4 and 30 sec.
3.
max age-The max age timer controls the maximum length of time that passes before a
bridge port saves its configuration BPDU information. This time is 20 sec by default, but you can tune the
time to be between 6 and 40 sec.
Reference: http://www.cisco.com/warp/public/473/122.html#stp_timers

QUESTION 169
You need to explain the RSTP port roles to your junior network administrator.
What statement is correct about these roles?
A. The root port is the switch port on every non-root bridge that is the chosen path to the root bridge. There can only one root port on every switch. The root port assumes the forwarding state in a stable active topology.
B. The designated port is the switch port on every non-root bridge that is the chosen path to the root bridge. There can be only one designated port on every switch. The designated port assumes the forwarding state in a stable active topology. All switches connected to a give segment listen to all BPDUs and determine the switch that will be root switch for a particular segment.
C. The backup port is a switch port that offers an alternate path toward the root bridge. The Backup port assumes a discarding state in a stable, active topology. The backup port will be present on non-designated switches and will make a transition to a designated port of the current designated path fails.
D. The disabled port is an additional switch port on the designated switch the redundant link to the segment for which the switch is designated. A disabled port has a higher port ID than the disabled port on the designated switch. The disabled port assumes the discarding state in a stable active topology.
E. None of the above

Correct Answer: A Section: (none) Explanation
Explanation/Reference:
Explanation:
Brief Summary of STPPortRoles
Internally, STP assigns to each bridge (or switch) port a role that is based on configuration, topology,
relative position of the port in the topology, and other considerations. The port role defines the behavior of
the port from the STP point of view.
Based on the port role, the port either sends or receives STP BPDUs and forwards or blocks the data

traffic. This list provides a brief summary of each STP port role:
1.
Designated-One designated port is elected per link (segment). The designated port is the port closest to the root bridge. This port sends BPDUs on the link (segment) and forwards traffic towards the root bridge. In an STP converged network, each designated port is in the STP forwarding state.

2.
Root-The bridge can have only one root port. The root port is the port that leads to the root bridge. In an STP converged network, the root port is in the STP forwarding state.

3.
Alternate-Alternate ports lead to the root bridge, but are not root ports. The alternate ports maintain the STP blocking state.

4.
Backup-This is a special case when two or more ports of the same bridge (switch) are connected together, directly or through shared media. In this case, one port is designated, and the remaining ports block. The role for this port is backup. Reference: http://www.cisco.com/en/US/tech/ CK3 89/ CK6 21/technologies_tech_note09186a0080094640.shtml
QUESTION 170
The Certkiller network utilizes the Multiple-instance Spanning Tree protocol in its switched LAN. Which three statements about the MST protocol (IEEE 802.1S) are true? (Select three)
A. To verify the MST configuration, the show pending command can be used in MST configuration mode.
B. When RSTP and MSTP are configured; UplinkFast and BackboneFast must also be enabled.
C. All switches in the same MST region must have the same VLAN-to-instance mapping, but different configuration revision numbers.
D. All switches in an MST region, except distribution layer switches, should have their priority lowered from the default value 32768.
E. An MST region is a group of MST switches that appear as a single virtual bridge to adjacent CST and MST regions.
F. Enabling MST with the “spanning-tree mode mst” global configuration command also enables RSTP.

Correct Answer: AEF Section: (none) Explanation
Explanation/Reference:
Explanation:
MST is built on the concept of mapping one or more VLANs to a single STP instance.
Multiple instances of STP can be used (hence the name MST), with each instance supporting a different
group of VLANs.
Each could be tuned to result in a different topology, so that Instance 1 would forward on the left uplink,
while Instance 2 would forward on the right uplink. Therefore, VLAN A would be mapped to Instance 1,and
VLAN B to Instance 2.
To implement MST in a network, you need to determine the following:

1.
The number of STP instances needed to support the desired topologies.

2.
Whether to map a set of VLANs to each instance.
QUESTION 171
Certkiller uses MSTP within their switched LAN. What is the main purpose of Multiple Instance Spanning Tree Protocol (MSTP)?
A. To enhance Spanning Tree troubleshooting on multilayer switches
B. To reduce the total number of spanning tree instances necessary for a particular topology
C. To provide faster convergence when topology changes occur in a switched network
D. To provide protection for STP when a link is unidirectional and BPDUs are being sent but not received
E. None of the above

Correct Answer: B Section: (none) Explanation
Explanation/Reference:
Explanation:
MST is built on the concept of mapping one or more VLANs to a single STP instance.
Multiple instances of STP can be used (hence the name MST), with each instance supporting a different
group of VLANs.
Each could be tuned to result in a different topology, so that Instance 1 would forward on the left uplink,
while Instance 2 would forward on the right uplink. Therefore, VLAN A

would be mapped to Instance 1,and VLAN B to Instance 2.
To implement MST in a network, you need to determine the following:

1.
The number of STP instances needed to support the desired topologies.

2.
Whether to map a set of VLANs to each instance.
QUESTION 172
Which of the following specifications is a companion to the IEEE 802.1w Rapid Spanning Tree Protocol (RSTP) algorithm, and warrants the use multiple spanning-trees?
A. IEEE 802.1s (MST)
B. IEEE 802.1Q (CST)
C. Cisco PVST+
D. IEEE 802.1d (STP)
E. None of the above

Correct Answer: A Section: (none) Explanation
Explanation/Reference:
Explanation: MST uses the modified RSTP version called the Multiple Spanning Tree Protocol (MSTP). MST extends the IEEE 802.1w rapid spanning tree (RST) algorithm to multiple spanning trees. This extension provides both rapid convergence and load balancing in a VLAN environment. MST converges faster than PVST+. MST is backward compatible with 802.1D STP, 802.1w (rapid spanning tree protocol [RSTP]), and the Cisco PVST+ architecture. MST allows you to build multiple spanning trees over trunks. You can group and associate VLANs to spanning tree instances. Each instance can have a topology independent of other spanning tree instances. This new architecture provides multiple forwarding paths for data traffic and enables load balancing. Network fault tolerance is improved because a failure in one instance (forwarding path) does not affect other instances (forwarding paths). In large networks, you can more easily administer the network and use redundant paths by locating different VLAN and spanning tree instance assignments in different parts of the network. A spanningtree instance can exist only on bridges that have compatible VLAN instance assignments. You must configure a set of bridges with the same MST configuration information, which allows them to participate in a specific set of spanning tree instances. Interconnected bridges that have the same MST configuration are referred to as an MST region. Reference: http://www.cisco.com/en/US/products/hw/switches/ps708/ products_configuration_guide_chapter09186a008007 e
QUESTION 173
Which of the following specification will allow you to: associate VLAN groups to STP instances so you can provide multiple forwarding paths for data traffic and enable load balancing?
A. IEEE 802.1d (STP)
B. IEEE 802.1s (MST)
C. IEEE 802.1Q (CST)
D. IEEE 802.1w (RSTP)

Correct Answer: B Section: (none) Explanation Explanation/Reference:
Explanation: IEEE 802.1s MST Overview MST extends the IEEE 802.1w rapid spanning tree (RST) algorithm to multiple spanning trees. This extension provides both rapid convergence and load balancing in a VLAN environment. MST converges faster than PVST+. MST is backward compatible with 802.1D STP, 802.1w (rapid spanning tree protocol [RSTP]), and the Cisco PVST+ architecture. Reference: http://www.cisco.com/en/US/products/hw/switches/ps708/ products_configuration_guide_chapter09186a008007 e
QUESTION 174
Which three items are configured in MST configuration submode? (Select three)
A. Region name
B. Configuration revision number
C. VLAN instance map
D. IST STP BPDU hello timer
E. CST instance map
F. PVST+ instance map

Correct Answer: ABC Section: (none) Explanation
Explanation/Reference:
Explanation:
spanning-tree mst configuration:
Use the spanning-tree mst configuration command to enter the MST configuration submode. Use the no
form of this command to return to the default MST configuration.
Defaults:
The default value for the MST configuration is the default value for all its parameters:

1.
No VLANs are mapped to any MST instance (all VLANs are mapped to the CIST
instance).
2.
The region name is an empty string.
3.
The revision number is 0.
Usage Guidelines:
The MST configuration consists of three main parameters:

1.
Instance VLAN mapping (see the instance command)
2.
Region name (see the name command)
3.
Configuration revision number (see the revision command)

QUESTION 175
By default, all VLANs will belong to which MST instance when using Multiple STP?
A. MST00
B. MST01
C. the last MST instance configured
D. none

Correct Answer: A Section: (none) Explanation
Explanation/Reference:
Explanation: Recall that the whole idea behind MST is the capability to map multiple VLANs to a smaller number of STP instances. Inside a region, the actual MST instances (MSTIs) exist alongside the IST. Cisco supports a maximum of 16 MSTIs in each region. IST always exists as MSTI number 0, leaving MSTI 1 through 15 available for use. By default all VLANs are belonged to MST00 instance.
QUESTION 176
Which MST configuration statement is correct?
A. MST configurations can be propagated to other switches using VTP.
B. After MST is configured on a Switch, PVST+ operations will also be enabled by default.
C. MST configurations must be manually configured on each switch within the MST region.
D. MST configurations only need to be manually configured on the Root Bridge.
E. MST configurations are entered using the VLAN Database mode on Cisco Catalyst switches.

Correct Answer: C Section: (none) Explanation
Explanation/Reference:
Explanation:
MST configuration must be manually be configured on each switch within the MST region.

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