OSPF

※ Router Role ※

Internal Router
Backbone Router
Area Border Router
Autonomous System Border Routers

※ Neighbour & Adjacency ※

Down	沒發Hello
Init	剛向對方發Hello
2-Way (Neighbor)	DROTHER終點, 選DR/BDR
ExStart	預備交換Link State
ExChange	給對方LSA Menu(DBD)
Loading	正在交換LSA
Full (Adjacency)	同Area的Topo是一樣

※ LSA ※

LSA 1 (From/To: 同Area所有Router)	自己的 (neighbor+Cost)
LSA 2 (From: DR, To: non-DR)	DR的 (neighbor+Cost)
LSA 3 (From: ABR, To: 同Area所有Router)	ABR的 (network+Cost)
LSA 4 (From: ABR, To: 同Area所有Router)	ABR的 (ASBR+Cost)
LSA 5 (From: ASBR, To: OSPF所有Router)	ASBR的 (network+Cost)

※ Route Table 表示 ※

O IA 192.168.12.0/24 [110/20]

IA: 誇Area
E2: Advertise Metric
E1: Advertise Metric + neighbor cost
110: AD
20: Metric

E2:
R1(config-router)# redistribute eigrp 100 metric-type 2 metric 99
E1:
R1(config-router)# redistribute eigrp 100 metric-type 1 metric 99

※ Stub Area ※

Stubby Area (All route next hops are the same, why not combine? External route -> 0.0.0.0 LSA3)
- 把LSA4/5化成LSA3
- O E2 192.168.67.0/24 [110/20] via 192.168.12.2
- O*IA 192.168.0.0/0 [110/11] via 192.168.12.2
Totally Stubby Area (把all LSA3都化成0.0.0.0)
- 把LSA4/5化成LSA3, 然後再把LSA3都化成0.0.0.0
- O IA 192.168.12.0/24 [110/20] via 192.168.12.2
- O*IA 0.0.0.0/0 [110/11] via 192.168.12.2
Not So Stubby Area (NSSA) (stub連接External Network時用, external route -> LSA 7 N route)
- 把LSA4/5化成LSA7 (去External Network)
- O E2 192.168.67.0/24 [110/20] via 192.168.56.6
- O N2 192.168.67.0/24 [110/20] via 192.168.56.6
Totally Not So Stubby Area (LSA7連去External Network)(LSA3連去Internal Network) (把LSA3都化成0.0.0.0 and keep LSA 7 N route)
- 把LSA4/5化成LSA7, LSA3都化成0.0.0.0
- O IA 192.168.34.0/24 [110/20] via 192.168.56.6
- O*IA 0.0.0.0/0 [110/11] via 192.168.45.4

R1(config-router)# area stub
R1(config-router)# area stub no-summary
R1(config-router)# area nssa
R1(config-router)# area nssa no-summary

※ Metric ※

Metric = Cost + Cost + Cost…
Cost = (Reference BW, 100Mbit) / Interface BW

R1(config-if)# ip ospf cost 50 (把cost變成50)
R1(config-if)# bandwidth 5000 (把bandwidth變成5Mbit)
R1(config-router)# auto-cost reference-bandwidth 1000 (把bandwidth變成1000Mbit)

※ Route選舉 ※

O > O IA > E1/N1 > E2/N2

※ Load Balancing ※

相同Metric
maximum-paths <no of path>, max.16

※ Virtual Link ※

把其他Area與Area 0連起來, 或把兩個Area 0相連
area virtual-link 3.3.3.3

※ Summarisation ※

ABR
Area Range (同時產生Null Route)

R1(config-router)# area 0 range 172.16.0.0 255.255.254.0
R1(config-router)# no discard-route internal //去除Null Route

ASBR
Summary Address (同時產生Null0 Route)

R1(config-router)# summary-address 172.16.2.0 255.255.254.0
R1(config-router)# no discard-route external //去除Null Route

※ 優化 ※

Pacing Timer

問題: OSPF每1800秒就重新發佈Link State 解決: 每次重新發佈一條Link State很浪費CPU, 相約buffer 240秒後一起發佈	timers pacing lsa-group 240
問題: Link State放到interface的LSA Flood List一個一個發出解決: 每33msecs發一次Update Packet一次過update	timers pacing flood 33
問題: 發出LSA後, 對方回傳ACK表示收到LSA, 如沒回傳就retransmission 解決: Retansmission time 更改	timers pacing retransmission 100

SPF Throttle Timer

問題:
SPF有時會突然收到大量的Link State 改變, 浪費CPU
解決: 等待hold time一次過處理, Initial (處理第一波Link State Event)|Increment(處理之後波Link State Event)|max wait

timers throttle spf 10000 20000 100000, msecs, 初始hold時間, 下次event來時加holding time, 最多hold時間

LSA Throttle Timer

問題:
Router 因Local Link改變而產生LSA, 浪費CPU
解決: 等待hold time一次過處理, Initial (處理第一波Link State Event)|Increment(處理之後波Link State Event)|max wait

timers throttle lsa 20000 30000 50000, msecs, 初始hold時間, 下次event來時加holding time, 最多hold時間