350-001 CCIE Routing and Switching Written Exam v4.0

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Question 1

Which statement is true about TCN propagation?

  • A. The originator of the TCN immediately floods this information through the network.
  • B. The TCN propagation is a two step process.
  • C. A TCN is generated and sent to the root bridge.
  • D. The root bridge must flood this information throughout the network.


Answer : C

Explanation: Explanation New Topology Change Mechanisms When an 802.1D bridge detects a topology change, it uses a reliable mechanism to first notify the root bridge. This is shown in this diagram:

Once the root bridge is aware of a change in the topology of the network, it sets the TC flag on the BPDUs it sends out, which are then relayed to all the bridges in the network. When a bridge receives a BPDU with the TC flag bit set, it reduces its bridging-table aging time to forward delay seconds. This ensures a relatively quick flush of stale information. Refer to Understanding Spanning-Tree Protocol Topology Changes for more information on this process. This topology change mechanism is deeply remodeled in RSTP. Both the detection of a topology change and its propagation through the network evolve. Topology Change Detection In RSTP, only non-edge ports that move to the forwarding state cause a topology change. This means that a loss of connectivity is not considered as a topology change any more, contrary to 802.1D (that is, a port that moves to blocking no longer generates a TC). When a RSTP bridge detects a topology change, these occur: It starts the TC While timer with a value equal to twice the hello-time for all its non-edge designated ports and its root port, if necessary. It flushes the MAC addresses associated with all these ports. Note: As long as the TC While timer runs on a port, the BPDUs sent out of that port have the TC bit set. BPDUs are also sent on the root port while the timer is active. Topology Change Propagation When a bridge receives a BPDU with the TC bit set from a neighbor, these occur: It clears the MAC addresses learned on all its ports, except the one that receives the topology change. It starts the TC While timer and sends BPDUs with TC set on all its designated ports and root port (RSTP no longer uses the specific TCN BPDU, unless a legacy bridge needs to be notified). This way, the TCN floods

Question 2

Which two statements are true about PAgP? (Choose two.)

  • A. PaGP packets are sent with multicast group MAC address 01-80-c2-00-00-02.
  • B. PAgP uses the same multicast group MAC address as Cisco Discovery Protocol.
  • C. The PAgP protocol value is 0x0104.
  • D. During detection, PAgP packets are transmitted every 2 seconds.


Answer : B,C

Question 3

Which two of these are used in the selection of a root bridge in a network utilizing Spanning
Tree Protocol IEEE 802.1 D? (Choose two.)

  • A. Designated Root Cost
  • B. bridge ID priority
  • C. max age
  • D. bridge ID MAC address
  • E. Designated Root Priority
  • F. forward delay


Answer : B,D

Explanation: Explanation The root bridge of the spanning tree is the bridge with the smallest (lowest) bridge ID. Each bridge has a unique identifier (ID) and a configurable priority number; the bridge ID contains both numbers. To compare two bridge IDs, the priority is compared first. If two bridges have equal priority, then the MAC addresses are compared. For example, if switches A (MAC=0200.0000.1111) and B (MAC=0200.0000.2222) both have a priority of 10, then switch A will be selected as the root bridge. If the network administrators would like switch B to become the root bridge, they must set its priority to be less than 10.

Question 4

Which one of the following potential issues is eliminated by using split horizon?

  • A. Joined horizons
  • B. Packet forwarding loops
  • C. cisco Express Forwarding load-balancing inconsistency
  • D. Asymmetric routing throughout the network


Answer : B

Explanation: Split horizon is a base technique used to reduce the chance of routing loops. Split horizon states that it is never useful to send information about a route back in the direction from which the information came and therefore routing information should not be sent back to the source from which it came. In fact, only the interfaces are considered for the direction, not the neighbors. Note that this rule works well not only for routes learned via a distance vector routing protocol but also for routes installed in a routing table as directly connected networks. As they reside on the same network, the neighbors do not need any advertisements on a path to that shared network. The split horizon rule helps prevent two-node (two-neighbor) routing loops and also improves performance by eliminating unnecessary updates.

Question 5

For the following items, what is the mathematical relationship between the committed
information rate (CIR), committed burst (Bc), and committed rate measurement interval
(Tc)?

  • A. CIR = TC / Bc
  • B. CIR = Be / Tc
  • C. Tc = CIR / Bc
  • D. Tc = Bc / CIR


Answer : D

Explanation: Terminologies: The term CIR refers to the traffic rate for a VC based on a business contract. Tc is a static time interval, set by the shaper. Committed burst (Bc) is the number of bits that can be sent in each Tc. Be is the excess burst size, in bits. This is the number of bits beyond Bc that can be sent after a period of inactivity.

Question 6

For the following ports, which port is on every bridge in a Spanning Tree Protocol IEEE
802.1w network except the root bridge?

  • A. Root port
  • B. Backup port
  • C. Designated port
  • D. Alternate port


Answer : A

Explanation: Explanation The root bridge does not have a root port as this is the port on all non-root bridges that is used to communicate with the root bridge. All ports on the root bridge are designed ports. Reference http://www.cisco.com/en/US/tech/tk389/tk621/technologies_configuration_example09186a 008009467c.shtml#maintask1

Question 7

Before inserting a new switch in the network, the network administrator checks that the
VTP domain name is correct, the VTP mode is set to server, and revision is lower than the
switches in the network. The administrator then configures interfaces and trunks, erases
existing VLANs, and connects the switch to the network. Following that procedure, there is
no connectivity in the network. What is a possible cause of this problem?

  • A. Because the configuration revision of the new switches is lower than the rest of the network, it can change the VLAN database of the other switches.
  • B. As a VTP server, the new switch deleted all VLANs of the network.
  • C. Erasing VLANs increases the VTP configuration revision.
  • D. Since the configuration revision of the network is higher than the new switch, the VLAN database was automatically synchronized.


Answer : C

Explanation: Reset the Configuration Revision Number You can easily reset the configuration revision number by either of the two procedures provided in this section. Reset the Configuration Revision using Domain Name Complete these steps in order to reset the configuration revision number with the change of the domain name: 1. Issue "show vtp domain" in order to see that the configuration is empty 2. Configure the VTP Domain name 3. Change the VTP Domain back 4. Change the VTP Domain to what it was in step 2 Reset the Configuration Revision using VTP Mode Complete these steps in order to reset the configuration revision number with the change of the domain name: 1. Issue "show vtp domain" in order to see that the configuration is empty 2. Configure the VTP Domain name 3. Change the VTP mode from server to transparent 4. Change the VTP mode from transparent to server or client. Reference http://www.cisco.com/en/US/tech/tk389/tk689/technologies_tech_note09186a0080890613. shtml#topic9

Question 8

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 9

Refer to the exhibit. In the diagram, the switches are running IEEE 802.1s MST. Which
ports are in the MST blocking state?


  • A. GE-1/2andGE2/1
  • B. GE-1/1 and GE-2/2
  • C. GE-3/2 and GE 4/1
  • D. no ports are in the blocking state
  • E. There is not enough information to determine which ports are in the blocking state.


Answer : A

Explanation: Switches Dist-1 & 2 will have no ports in a blocking stating. However, switches WC-1 & 2 will have the secondary ports Ge1/2 & Ge2/1 in an Alternate/Blocking state as this will be backup ports for the root port. Ge1/2 & Ge2/1 will transition to a forwarding state and become root ports if ports Ge1/1 & Ge2/2 go down. Multiple Spanning Tree (MST) is an IEEE standard inspired from the Cisco proprietary Multiple Instances Spanning Tree Protocol (MISTP) implementation. The main enhancement introduced by MST is that several VLANs can be mapped to a single spanning tree instance. This raises the problem of how to determine which VLAN is to be associated with which instance. More precisely, how to tag BPDUs so that the receiving devices can identify the instances and the VLANs to which each device applies. MST Configuration and MST Region Each switch running MST in the network has a single MST configuration that consists of these three attributes: 1. An alphanumeric configuration name (32 bytes) 2. A configuration revision number (two bytes) 3. A 4096-element table that associates each of the potential 4096 VLANs supported on the chassis to a given instance In order to be part of a common MST region, a group of switches must share the same configuration attributes. It is up to the network administrator to properly propagate the configuration throughout the region. Currently, this step is only possible by the means of the command line interface (CLI) or through Simple Network Management Protocol (SNMP). Other methods can be envisioned, as the IEEE specification does not explicitly mention how to accomplish that step. Note: If for any reason two switches differ on one or more configuration attribute, the switches are part of different regions. For more information refer to the Region Boundary section of this document. Reference http://www.cisco.com/en/US/tech/tk389/tk621/technologies_white_paper09186a0080094cf c.shtml

Question 10

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: 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 span tree guard loop command. Note When you are in MST mode, you can set all the ports on a switch with the set span tree 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-enab

Question 11

Which two combinations are valid PAgP configurations that will set up a PAgP channel?
(Choose two.)

  • A. On-Passive
  • B. On-Auto
  • C. Passive-Active
  • D. Desirable-Auto
  • E. Active-Active
  • F. Desirable-Desirable


Answer : D,F

Question 12

The network administrator wants to enable an EtherChannel between two switches in "on"
mode. The administrator connects the cables and enables the interfaces, but while
configuring the EtherChannel in the first switch, a spanning-tree loop was detected. Which
two of these procedures can avoid this problem? (Choose two.)

  • A. Configure the EtherChannel as "desirable" first.
  • B. Assign all interfaces to the same VLAN.
  • C. Disable PortFast on the interfaces in the EtherChannels.
  • D. Disable all interfaces first.
  • E. Fast Ethernet and Gigabit Ethernet ports cannot be assigned to the same EtherChannel.
  • F. Fix cabling problems.


Answer : C,D

Explanation: If a workstation or a server is connected with a single Network Interface Card (NIC) to a switch port, this connection cannot create a physical loop. These connections are considered leaf nodes. There is no reason to make the workstation wait 30 seconds while the switch checks for loops when the workstation cannot cause a loop. With the addition of the PortFast or fast-start feature, the STP for this port assumes that the port is not part of a loop. In this case, the port immediately moves to the forwarding state, and skips the blocking, listening, or learning states. This command does not turn STP off. This command makes STP skip a few steps in the beginning on the selected port, although unnecessary in this circumstance. Note: The PortFast feature must never be used on switch ports that connect to other switches, hubs, or routers. These connections can cause physical loops, and it is very important that Spanning Tree go through the full initialization procedure in these situations. A Spanning Tree loop can bring the network down. If the PortFast feature is turned on for a port that is part of a physical loop, it can cause packets to be continuously forwarded and even multiply in such a way that the network cannot recover. Reference https://supportforums.cisco.com/docs/DOC-4897

Question 13

Which of these best describes the actions taken when a VTP message is received on a
switch configured with the VTP mode "transparent"?

  • A. VTP updates are ignored and forwarded out all ports.
  • B. VTP updates are ignored and forwarded out trunks only.
  • C. VTP updates are made to the VLAN database and are forwarded out trunks only.
  • D. VTP updates are ignored and are not forwarded.


Answer : B

Explanation: Explanation You can configure a switch to operate in any one of these VTP modes: Server--In VTP server mode, you can create, modify, and delete VLANs and specify other configuration parameters, such as VTP version and VTP pruning, for the entire VTP domain. VTP servers advertise their VLAN configuration to other switches in the same VTP domain and synchronize their VLAN configuration with other switches based on advertisements received over trunk links. VTP server is the default mode. Client--VTP clients behave the same way as VTP servers, but you cannot create, change, or delete VLANs on a VTP client. Transparent--VTP transparent switches do not participate in VTP. A VTP transparent switch does not advertise its VLAN configuration and does not synchronize its VLAN configuration based on received advertisements, but transparent switches do forward VTP advertisements that they receive out their trunk ports in VTP Version 2. Off (configurable only in CatOS switches)--In the three described modes, VTP advertisements are received and transmitted as soon as the switch enters the management domain state. In the VTP off mode, switches behave the same as in VTP transparent mode with the exception that VTP advertisements are not forwarded. VTP V2 VTP V2 is not much different than VTP V1. The major difference is that VTP V2 introduces support for Token Ring VLANs. If you use Token Ring VLANs, you must enable VTP V2. Otherwise, there is no reason to use VTP V2. Changing the VTP version from 1 to 2 will not cause a switch to reload. VTP Password If you configure a password for VTP, you must configure the password on all switches in the VTP domain. The password must be the same password on all those switches. The VTP password that you configure is translated by algorithm into a 16-byte word (MD5 value) that is carried in all summary-advertisement VTP packets. VTP Pruning VTP ensures that all switches in the VTP domain are aware of all VLANs. However, there are occas

Question 14

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

  • A. On/On
  • B. On/Auto
  • C. Passive/Active
  • D. Desirable/Auto
  • E. Active/Active
  • F. Desirable/Desirable


Answer : A,C,E

Question 15

Which two statements are true about 802.1s? (Choose two.)

  • A. 802.1s supports a reduced number of spanning-tree instances.
  • B. 802.1s has better convergence times than 802.1w.
  • C. 802.1s does not support load balancing over the same physical topology.
  • D. The CPU utilization for 802.1s is lower than the CPU utilization for 802.1w.


Answer : A,D

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