わくわくIT資格勉強記

• 最大8つの物理リンクをまとめられる。
• SR内で最大64のLAGを作れる。
• Duplex, Speed は AutoNegoではくマニュアルで設定すること。
• active linkがn(0 - 7)本以下になったら
  • downさせる
  • OSPFのためのlink cost 再計算を行う
    • active linkの変化が有った都度行うことも可能

• default bridge priority: 32768

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When a frame with an unknown destination MAC address enters a switch, the switch will forward it out which ports?
　A. None
　B. All
　C. All unicast ports
　D. All except the port that received the frame

This is how switches work until they build up their FDB.

The primary difference in the way Ethernet hubs and Ethernet switches handle traffic is .
　A. Hubs forward broadcast traffic out every port, switches do not.
　B. Switches eliminate the need for thicknet cabling.
　C. Switches support multiple physical connections to hosts.
　D. Switches forward unicast traffic only to a specific destination port.

This is opposed to hubs that accty like a "wire in a box" and forward frames out every port. Both hubs and switches forward broadcast traffic out all ports.

Which of the following is not true about Link Aggregation Groups?
　A. They protect against single or multiple link failures.
　B. They can contain up to eight physical links.
　C. They can protect against a switch failure by calculating multiple paths to the root.
　D. They can be configured to enter a down state if a certain number of links in the bundle fail.

This is a description of STP, not LAG.

Which of the following is not true of the STP protocol?
　A. It calculates a root bridge.
　B. It uses a cost value on each port to determine the path to the root bridge.
　C. It ensures a loop-free topology.
　D. It provides load-sharing capability.

STP cannot provide load-sharing because only a single path exists between each segmanet and the root bridge to avoid loops.

The advantage of using VLANs is .
　A. They can increase the security of your network.
　B. They can interconnect multiple broadcast domains.
　C. They can limit the amount of broadcast traffic between groups of devices.
　D. A and C but not B

VLANs do not provide routing between broadcast domains although theyt do create separate broadcast domains.

Which of the following statements is false?
　A. Routers provice broadcast domain separation.
　B. Hubs provide collision domain separation.
　C. VLANs provide broadcast domain separation.
　D. Switches provide collision domain separation.

Hubs simply forward all frames out all ports and so do not provide collision domain separation.

The method that LAGs use to provide load balancing is best described as:
　A. Aggregates all source/destination conversations into a single conversation equally across all links
　B. Uses the same physical link for each source/destination conversation
　C. Statistically balances conversations based on the source MAC address
　D. Distributes egress frames equally across all links in the bundle

This method is used to ensure that there is no frame reordering as required by the 802.3ad standard.

Given the following code:
　Config> lag 1
　Config>lag# description "LAG from PE1 to PE2"
　Config>lag# port 1/1/1 1/1/2 1/1/3 1/1/4 1/1/5 1/1/6

同じ意味として "port 1/1/[1..6]" で指定可能

　Config>lag# port-threshold 2 action down

active link が 2 以下になったらdown

　Config>lag# dynamic-cost

link fail発生毎にOSPF link cost計算を行う

例:cost 100で active link 6 のうち 2 failの場合 cost 100/6 active link → 2 link fail → cost 100/4 active link

　Config>lag# no shutdown

Which answer correctly describes what happens when Ports 1/1/5 and 1/1/6 fail?
　A. Nothing because the port threshold of 2 active links has not been reached
　B. The LAG begins using equal costing across all links because of the dynamic-cost parameter.
　C. The LAG updates its BPDUs and recalculates STP.
　D. The LAG changes its OSPF cost for the bundle but takes no other action.

This is because the "dynamic-cost" option is configugred on the bundle so that each time a link fails, the OSPF cost is updated. No other action is taken because the threshold is 2 and there are still four out of six active links functioning.

What is the primary reason that Ethernet switched networks require STP?
　A. STP provide for link backup between switches.
　B. A loop-free topology is more efficient.
　C. Redundant paths can lead to broadcast storms and FDB instability.
　D. STP updates the OSPF routing protocol cost upon link failure.

This describes the problem of loops in a switched network, which is the primary reason to use STP.

The mechanism that STP uses to prevent loops in an Ethernet switched network is .
　A. STP elect a root and selectively blocks higher cost paths to the root from each bridge.
　B. STP blocks ports on all bridges that are not the root bridge.
　C. STP proactively changes all paths to the root bridge so that they are equal cost.
　D. STP uses BPDUs to set up a virtual path between each source and destination pair.

This is an accurate description of the way STP functions to prevent loops.

What determines how the root bridge is elected?
　A. The brirdge priority
　B. The MAC address of the lowest switch port
　C. The bridge priority unless there is a tie, and then the lowest MAC address
　D. The BID unless there are multiple bridge priorities that are equal

This is an accurate description of how a root bridge is selected. Answer D is wrong because the BID is always used to determine the root bridge (note the unless qualifier). In fact, answer C describes what the BID is: bridge priority plus MAC address.

What distinguishes an alternate port from a back-up port in STP?
　A. The alternate port has a higher path to the root.
　B. The back-up port has a lower priority.
　C. The back-up port is used only when the alternate port fails.
　D. The back-up port is on the same switch as the designated switch.

The alternate port is on a non-designated switch on the same segment.

Which of the following is false regarding VLANs?
　A. They provide for broadcat domain separation.
　B. A single VLAN can exist on multiple switches.
　C. They require a separate physical connection per VLAN for interswitch links.
　D. They use a 12-bit VLAN ID to identify each VLAN.

This is not true if a VLAN trunk is used between the swithces.

Which STP port state is characterized by the port accepting and recording MAC address information, but not forwarding any frames out the port?
　A. Blocking
　B. Forwarding
　C. Listening
　D. Learning

In this state, the bridge learns information about MAC addresses but does not yet forward frames.

The technology that allows multiple customers with the same VLANs to use the same provider backbone for their Ethernet traffic is known as .
　A. VLAN trunking
　B. VLAN tunneling
　C. VLAN stacking
　D. IEEE 802.1p

VLAN stacking allows a provider to stack its own VLAN information int front of the customer's VLAN information to support customers with overlapping VLANs.