OSPF
===

## 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