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# System prepended metadata

title: OSPF

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OSPF
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## 問答
1. What is the merit of using Multi-Area OSPF comparing to Single-Area?
    * routing table 較小
    * 比較少 link-state update，所以 memory 需要的比較少
    * 減少 SPF(Shortest Path First algorithm) 次數
2. Why the state of 1F-Aggre and 3F-Aggre adjacency in the multi-access topology (adjacency of interfaces that connect to the switch) stays at 2-Way instead of Full ?
    * 因為 DR 會收集與轉發 DBD 封包，所以 1F-Aggre 和 3F-Aggre 就不需要傳送給對方，因此維持在 2-Way state
3. What are the possible states of a adjancency
    * down state
    * init state
    * Two-Way state
    * ExStart state
    * Exchange state
    * Loading state
    * Full state
4. What is the LSA type of the packet that ChiaoTung-Core delivers the YangMing Campus routing information to 2F-Aggre ?
    * LSA Type 3
    * 因為 Type 3 會把其他 area 的資訊傳給同個 area 的其他 router
5. What is the LSA type of the packet that NYCU propogates default route from NYCU to 2F-Aggre ?
    * LSA Type 5
    * 因為 Type 5 會把 external network 傳給 OSPF 中的其他 router
6. Where can we set Stub Area ? What LSA type will be blocked then?
    * CSCC，因為下一步都是 ChiaoTung Campus
    * LSA Type 5，因為 Type 5 是用來傳送 external network 的