Open Shortest Path First
基本設定不像是 EIGRP 那樣有 Cisco Router 支援，而是眾多廠牌的路由器均有支援 OSPF，這使得 ISP 端大量採用 OSPF。
#router ospf + < process-id >
#network + < ip add > + < wildcard-mask area > + < area-id >
(1) 單一區域的 OSPF 設定
如下均在 single area 內
R2
/ \ 10.2.2.1 - R
10.1.1.1. 10.1.2.1 /
10.1.1.2 10.1.2.2 /
/ \ /
R3 R1(TPE)- 10.64.0.1 ------------- WAN ----------- 10.64.0.2 -(Tainan) R
| | \
10.1.3.1 10.1.3.2 \
\
10.2.3.2 - R
(2) R1 設定
R1#conf t
R1(config)#ospf 1
R1(config-router)#network 10.1.3.2 0.0.0.0 area 0
R1(config-router)#network 10.1.2.2 0.0.0.0 area 0
R1(config-router)#network 10.64.0.1 0.0.0.0 area 0
ctrl + Z
(3) 下指令 sh ip protocol 藉以檢視是否設定完成
R1#sh ip protocol
Routing Protocol is "ospf 1"
// 這台路由器的 process-id is 1
Redistributing: ospf 1
Routing for Networks:
10.1.3.2/32
10.1.2.2/32
10.64.0.1/32
// 目前尚未設定好其他路由器，所以尚未有大量資訊。（如 ）
(4) 顯示鄰近訊息
R1#sh cdp ne
DeviceId Local interface Holdtme Capability Platform Port ID
R2 s0 R
R3 s1 R
R-tainan e0 R
// capability:
// R - Router
// B - Source Route Bridge
// S - Switcher
// H - host
// I - IGMP
// r - repeater
(5) 利用 area-id 查看鄰近路由器資訊
R1#sh ip ospf neighbor detail
Neighbor 10.64.0.2
in the area 0 via interface E0
Neighbor Priority is 1, state is full.
Neighbor 10.1.3.1
in the area 0 via interface s0
Neighbor Priority is 1, state is full.
Neighbor 10.1.2.1
in the area 0 via interface s1
Neighbor Priority is 1, state is full.
(6) 顯示 ospf 的 LSA (Link state db) 鏈結狀態資料庫
R1#sh ip ospf database
ospf router with ID (router id is 10.64.0.1) (process id is 1)
Router Link State (Area 0)
Link ID ADV Router Age Seq# Checksum Link count
10.64.0.1 4
10.64.0.2 4
10.1.2.1 4
10.1.3.1 4
10.2.2.1 5
10.2.3.2 5
Net Link State (Area 0)
Link ID ADV Router Age Seq# Checksum
10.64.0.2 10.64.0.2 80 0X80000001 0X7990
(7) 查看 R1 學習到的路徑
R1#sh ip route
codec: O - OSPF
10.0.0.0/24 is subnetted, 7 subnets
C 10.1.3.0 is directly connected, s0
C 10.1.2.0 is directly connected, s1
C 10.64.0.0 is directly connected, e0
O 10.1.1.0 via 10.1.3.1, s0
via 10.1.2.1, s1
O 10.2.3.0 via 10.64.0.2, E0
O 10.2.2.0 via 10.64.0.2, E0
O 10.2.1.0 via 10.64.0.2, E0
(8) 觀看 routing info 訊息
R1# sh ip protocol
Redistributing: ospf
Routing for networks:
10.1.3.2/32
10.1.2.2/32
10.64.0.1/32
Routing info Source
GW Distance Last Update
10.1.2.1 110
10.2.3.2 110
10.1.3.1 110
10.2.2.1 110
10.64.0.2 110
distance : (default is 110)
(9) 詳見步驟 7, 能觀察到路由學習時，經過 10.1.1.0 網段的，可以透過 s0 出去經過 10.1.3.1 的 hops 或是 10.1.2.1 的 hops
O 10.1.1.0 via 10.1.3.1, s0
via 10.1.2.1, s1
(10) 調整介面成本 cost, 可藉由手動下指令，讓路由被動的選擇最佳路徑
R1#conf t
R1(config)#int s0
R1(config-if)# ip cost 50
// 將此介面降低成本 50
ctrl + Z
(11) 檢視結果
R1#sh ip route
10.0.0.0/24 is subnetted, 7 subnets
C 10.1.3.0 is directly connected, s0
C 10.1.2.0 is directly connected, s1
C 10.64.0.0 is directly connected, e0
O 10.1.1.0 via 10.1.3.1, s0 // s1 介面相對 s0 成本較高，故被過濾掉。
O 10.2.3.0 via 10.64.0.2, E0
O 10.2.2.0 via 10.64.0.2, E0
O 10.2.1.0 via 10.64.0.2, E0