Which statement is true about TCN propagation?
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:
Which two statements are true about PAgP? (Choose two.)
Answer : B,C
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.)
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.
Which one of the following potential issues is eliminated by using split horizon?
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.
For the following items, what is the mathematical relationship between the committed
information rate (CIR), committed burst (Bc), and committed rate measurement interval
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.
For the following ports, which port is on every bridge in a Spanning Tree Protocol IEEE
802.1w network except the root bridge?
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
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?
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
Which three options are considered in the spanning-tree decision process? (Choose three.)
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
Refer to the exhibit. In the diagram, the switches are running IEEE 802.1s MST. Which
ports are in the MST 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
Which statement is true about loop guard?
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
Which two combinations are valid PAgP configurations that will set up a PAgP channel?
Answer : D,F
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.)
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
Which of these best describes the actions taken when a VTP message is received on a
switch configured with the VTP mode "transparent"?
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
Which three combinations are valid LACP configurations that will set up a channel?
Answer : A,C,E
Which two statements are true about 802.1s? (Choose two.)
Answer : A,D