CCNA - STP, RSTP 快速生成樹協議 Rapid STP

CCNA - STP Port States (Spanning Tree Protocol)

STP Port States 五種狀態

0. Blocking 阻斷：接收但不轉發資料

1. Listening 監聽：不轉發，可收發BPDU
   在15秒的 Forward Delay Time 決定最佳路徑後
   Port 會依角色進入 Blocking 或 Learning

2. Learning 學習：不轉發，學習接到 Switch 的 MAC, Forward Delay Time 15秒

3. Forwarding 轉發：提供 lowest-cost 最短路徑到 Root Bridge
   同時學習 MAC 傳送封包資料

*. Disable 禁用狀態


CCNA - RSTP 快速生成樹協議 Rapid STP

Refer to the exhibit. Each of these four switches has been configured with a hostname, as well as being configured to run RSTP. No other configuration changes have been made. Which three of these show the correct RSTP port roles for the indicated switches and interfaces? (Choose three.) 
如圖所示。四個交換器都已經設定上了名字，並且都運行 RSTP。不改變其他設定。對於交換器和port，下列哪三個選項能夠正確的表達RSTP port的作用？
A. SwitchA, Fa0/2, designated  
B. SwitchA, Fa0/1, root
C. SwitchB, Gi0/2, root
D. SwitchB, Gi0/1, designated   
E. SwitchC, Fa0/2, root
F. SwitchD, Gi0/2, root


Answer: ABF

網路中只能有一個 root bridge
非根橋只能有一個 root port
分 段只能有一個 designated port
其餘為 blocking port

1. root bridge
priority 最小的被選取做為 root bridge，若 priority 相同時 MAC 最小為 root bridge
2. designated port
root bridge 上的 port 均為 designated port
非 root bridge 選 cost 較小的為 designated port
3. root port
每分段與 root bridge 最近的 port
4. 其他為 block port

速 解：switch 100M 速度為19, Gi 速度為4, 但 Fa+Gi = 100M = 19
1. ∵ MAC ∴ C 為 root bridge
2. A 到 C = A Fa0/1 到 C = 19
3. B 到 C = B Gi0/1 到 D Gi0/1 + D Gi0/2 到 C = 4+19 = 23
4. ∵19<23 ∴ A Fa0/2 為 designated port, B Gi0/2 為 block port


Which two values are used by Spanning Tree Protocol to elect a root bridge? (Choose two.)
在生成樹協議中，哪兩個選項是被用來選擇根bridge時使用的？
A. amount of RAM
B. bridge priority
C. IOS version
D. IP address
E. MAC address
F. speed of the links

Refer to the exhibit. Why has this switch not been elected the root bridge for VLAN1?
根據演示。為什麼交換器沒有被選舉成 VLAN1 的根bridge

A. It has more than one interface that is connected to the root network segment.
有多於一個的接口連接在根網路段
B. It is running RSTP while the elected root bridge is running 802.1d spanning tree.
當選舉根bridge的時候 RSTP 在運行，並且在運行 802.1d的生成樹
C. It has a higher MAC address than the elected root bridge.
跟已被選為根 bridge的交換器相比，這個交換器有更高的 MAC 地址
D. It has a higher bridge ID than the elected root bridge.
跟已被選為根 bridge的交換器相比，這個交換器有更高的bridge ID

Answer: D

Which two of these statements regarding RSTP are correct? (Choose two.)
下列對 RSTP 的描述哪兩項正確？
A. RSTP cannot operate with PVST+.
RSTP 不能運行PVST+
B. RSTP defines new port roles.
RSTP 定義了一個新的port任務
C. RSTP defines no new port states.
RSTP 沒有定義新的port狀態
D. RSTP is a proprietary implementation of IEEE 802.1D STP.
RSTP 屬於 IEEE 802.1D STP 的私有
E. RSTP is compatible with the original IEEE 802.1D STP.
RSTP 與原先的 IEEE 802.1D STP 是兼容的

Answer: BE