ActualTests.Cisco.640-802.Exam.Q.and.A.08.15.08-DDU (1130589), страница 22
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Certkiller A port that connects to Certkiller DB. Certkiller A port that connects to Certkiller BC. Certkiller A port that connects to Certkiller CD. Certkiller B port that connects to Certkiller CE. Certkiller B port that connects to Certkiller DF. Certkiller D port that connects to Certkiller AAnswer: A, B, EExplanation:STP uses the concept of cost to determine many things. Selecting a Root Port involvesevaluating the Root Path Cost. This value is the cumulative cost of all the links leading tothe Root Bridge.
A particular switch link has a cost associated with it, too, called the PathCost. To understand the difference between these values, remember that only the RootPath Cost is carried inside the BPDU. As the Root Path Cost travels along, other switchescan modify its value to make it cumulative. The Path Cost, however, is not contained inthe BPDU. It is known only to the local switch where the port (or "path" to a neighboringActualtests.com - The Power of Knowing640-802switch) resides.Path Costs are defined as a 1-byte value, with the default values shown in Table 9-3.Generally, the higher the bandwidth of a link, the lower the cost of transporting dataacross it.
The original IEEE 802.1D standard defined Path Cost as 1000 Mbps divided bythe link bandwidth in Mbps. These values are shown in the center column of the table.Modern networks commonly use Gigabit Ethernet and OC-48 ATM, which are botheither too close to or greater than the maximum scale of 1000 Mbps. The IEEE now usesa nonlinear scale for Path Cost, as shown in the right column of the table.All Remaining ports then root will be in blocking mode.QUESTION 185:Two Certkiller switches are shown below:This network is stable and operating properly.
Assuming that default STPconfigurations are running on both switches, which port will be in blocking mode?A. Port Fa0/1 on Certkiller 1B. Port Fa0/2 on Certkiller 1C. Port Fa0/1 on Certkiller 2D. Port Fa0/2 on Certkiller 2Answer: AExplanation:Spanning-Tree Protocol (STP) is a Layer 2 protocol that utilizes a special-purposealgorithm to discover physical loops in a network and effect a logical loop-free topology.STP creates a loop-free tree structure consisting of leaves and branches that span theentire Layer 2 network. The actual mechanics of how bridges communicate and how theSTP algorithm works will be discussed at length in the following topics.
Note that theterms bridge and switch are used interchangeably when discussing STP. In addition,unless otherwise indicated, connections between switches are assumed to be trunks.The switches move on to selecting Root Ports. The Root Port of a bridge is the port thatActualtests.com - The Power of Knowing640-802is closest to the Root Bridge in terms of Path Cost. Every non-Root Bridge must selectone Root Port.
Again, bridges use the concept of cost to measure closeness. As with somerouting metrics, the measure of closeness using STP is not necessarily reflected by hopcount. Specifically, bridges track what is referred to as Root Path Cost, which is thecumulative cost of all links to the Root Bridge. So, Answer A is correct.QUESTION 186:Exhibit:Exhibit:Please study the exhibit carefully. How can a network administrator ensure that theSTP election process would result in Certkiller B being elected as the root switch?A. Clear the Certkiller B STP revision number.B. Assign Certkiller B a low priority number.C.
Increase the Certkiller B priority number.D. Change the MAC address of Certkiller BAnswer: BExplanation:An election process among all connected switches chooses the Root Bridge. Each switch has a uniqueBridge ID that identifies it to other switches. The Bridge ID is an 8-byte value consisting of the followingfields: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) onevery Catalyst switch.MAC Address 6 bytes-The MAC address used by a switch can come from the Supervisormodule, the backplane, or a pool of 1024 addresses that are assigned to every Supervisoror backplane depending on the switch model.
In any event, this address is hardcoded andunique, and the user cannot change it.When a switch first powers up, it has a narrow view of its surroundings and assumes that it is the RootBridge itself. This notion will probably change as other switches check in and enter the election process.The election process then proceeds as follows: Every switch begins by sending out BPDUs with a RootBridge ID equal to its own Bridge ID and a Sender Bridge ID of its own Bridge ID. The Sender Bridge IDsimply tells other switches who is the actual sender of the BPDU message. (After a Root Bridge is decidedupon, configuration BPDUs are only sent by the Root Bridge. All other bridges must forward or relay theBPDUs, adding their own Sender Bridge Ids to the message.) Received BPDU messages are analyzed toActualtests.com - The Power of Knowing640-802see if a "better" Root Bridge is being announced.
A Root Bridge is considered better if the Root Bridge IDvalue is lower than another. Again, think of the Root Bridge ID as being broken up into Bridge Priority andMAC address fields. If two Bridge Priority values are equal, the lower MAC address makes the Bridge IDbetter. When a switch hears of a better Root Bridge, it replaces its own Root Bridge ID with the RootBridge ID announced in the BPDU. The switch is then required to recommend or advertise the new RootBridge ID in its own BPDU messages; although, it will still identify itself as the Sender Bridge ID.QUESTION 187:Which of the following components must be elected before the Spanning TreeProtocol can converge in a switched LAN?A.
Designated ports.B. Duplex operating mode.C. Fast mode ports.D. Root bridge.E. Root ports.F. BDPU priority.Answer: A, D, EExplanation:Designated port: Either a root port or a port that has been determined as having the best (lower) cost-adesignated port will be marked as a forwarding port.Root bridge: The root bridge is the bridge with the best bridge ID. With STP, the key is for all the switchesin the network to elect a root bridge that becomes the focal point in the network.
All other decisions in thenetwork-like which port is to be blocked and which port is to be put in forwarding mode-are made from theperspective of this root bridge.Root port: Always the link directly connected to the root bridge, or the shortest path to the root bridge. Ifmore than one link connects to the root bridge, then a port cost is determined by checking the bandwidth ofeach link. The lowest cost port becomes the root port.So these three components must be elected before the spanning tree protocol canconverge in a switched LANQUESTION 188:Why would the Certkiller administrator change the value of the spanning-treepriority of a switch?A.
in order to optimize the path that frames take from source to destinationB. to increase the priority so a designated port will become a root portC. to increase the BID, so the switch is more likely to become root bridgeD. in order to allow VLANs to be sent from one switch to another across a single linkE. to force a given switch to become an STP serverActualtests.com - The Power of Knowing640-802F.
None of the aboveAnswer: AExplanation:The Bridge Priority is used to measure the preference of a bridge in the spanning-treeAlgorithm. The possible values range between 0 and 65,535. The default setting is32,768. By adjusting the priority, the root bridge can be manually assigned to meet theneeds of the network administrator.QUESTION 189:What value is primarily used to determine which port becomes the root port oneach nonroot switch in a spanning-tree topology?A. path costB.
lowest port MAC addressC. VTP revision numberD. highest port priority numberE. port priority number and MAC addressF. None of the aboveAnswer: AExplanation:At the conclusion of the root bridge election process, the switches move on to selectingRoot Ports. The Root Port of a bridge is the port that is closest to the Root Bridge interms of Path Cost. Every non-Root Bridge must select one Root Port. Again, bridges usethe concept of cost to measure closeness.
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