ospf路徑選擇實驗
相關知識：
cost值=各路由 （10^8）/BW相加
show interface *(e1/0) 可以查看BW等值
show ip ospf interface *（e1/0) 查看該接口的cost值
修改帶寬（DW），修改分子(默認位10^8),直接修
改接口的cost。，達到負載均衡，決定路徑走向。
修改方法：
帶寬修改：
enable
conf t
interface *(e0)
bandwidth *（帶寬值）
分子修改
enable
conf t
router ospf 100
auto-cost reference-bandwidth 1000
100M=10^8,1000既修改爲10^9，而且修
改一個路由，所有路由都要修改
cost口修改
enable
conf t
interface *(e0)
ip ospf cost *(值）
實驗平臺：思科官方PT5.0或DY模擬器
相關知識：
cost值=各路由 （10^8）/BW相加
show interface *(e1/0) 可以查看BW等值
show ip ospf interface *（e1/0) 查看該接口的cost值
修改帶寬（DW），修改分子(默認位10^8),直接修
改接口的cost。，達到負載均衡，決定路徑走向。
修改方法：
帶寬修改：
enable
conf t
interface *(e0)
bandwidth *（帶寬值）
分子修改
enable
conf t
router ospf 100
auto-cost reference-bandwidth 1000
100M=10^8,1000既修改爲10^9，而且修
改一個路由，所有路由都要修改
cost口修改
enable
conf t
interface *(e0)
ip ospf cost *(值）
實驗平臺：思科官方PT5.0或DY模擬器
基本配置：
enable
conf t
no ip domain-lookup
exec-timeout 0 0
logging synch
exit
hostname
R2配置：
enable
conf t
interface S0/0
no shutdown
ip address 12.0.0.2 255.255.255.0
clock rate 64000
interface S0/1
no shutdown
ip address 24.0.0.2 255.255.255.0
clock rate 64000
exit
router ospf 100
network 12.0.0.0 0.0.0.255 area 0
network 24.0.0.0 0.0.0.255 area 0
R1配置：
enable
conf t
interface S0/0
no shutdown
ip address 12.0.0.1 255.255.255.0
clock rate 64000
interface S0/1
no shutdown
ip address 13.0.0.1 255.255.255.0
clock rate 64000
exit
router ospf 100
network 12.0.0.0 0.0.0.255 area 0
network 13.0.0.0 0.0.0.255 area 0
R3配置：
enable
conf t
interface S0/0
no shutdown
ip address 13.0.0.3 255.255.255.0
clock rate 64000
interface S0/1
no shutdown
ip address 35.0.0.3 255.255.255.0
clock rate 64000
exit
router ospf 100
network 13.0.0.0 0.0.0.255 area 0
network 35.0.0.0 0.0.0.255 area 0
R4配置:
enable
conf t
interface S0/0
no shutdown
ip address 24.0.0.4 255.255.255.0
clock rate 64000
interface e1/0
no shutdown
ip address 45.0.0.4 255.255.255.0
exit
router ospf 100
network 24.0.0.0 0.0.0.255 area 0
network 45.0.0.0 0.0.0.255 area 0
R5配置：
enable
conf t
interface S0/0
no shutdown
ip address 35.0.0.5 255.255.255.0
clock rate 64000
interface e1/0
no shutdown
ip address 45.0.0.5 255.255.255.0
interface loopback 0
ip address 5.5.5.5 255.255.255.255
no shutdown
exit
router ospf 100
network 13.0.0.0 0.0.0.255 area 0
network 35.0.0.0 0.0.0.255 area 0
network 5.5.5.5 0.0.0.0 area 0
以R2到R5的lookback0爲例，有兩條路徑，各路由cost值和小的爲R2選擇的路徑，所以要改變ospf的路徑，就要修改數據使cost值變化決定路徑走向
以直接修改cost值選路徑爲例：
cost值=各路由 （10^8）/BW相加
R2/R4/R5路由
s0/1* MTU 1500 bytes, BW 1544 Kbit, DLY 20000 usec,
e1/0* MTU 1500 bytes, BW 10000 Kbit, DLY 1000 usec,
loo0* MTU 1514 bytes, BW 8000000 Kbit, DLY 5000 usec,
10^8/(1544*1000)=64.77
10^8/(10000*1000)=10
10^8/(8000000*1000)=0.0125
C=64.77+10+0.0.125≈75
R2/R1/R3/R5路由
s0/0 & MTU 1500 bytes, BW 1544 Kbit, DLY 20000 usec,
s0/1 & MTU 1500 bytes, BW 1544 Kbit, DLY 20000 usec,
s0/1 & MTU 1500 bytes, BW 1544 Kbit, DLY 20000 usec,
loo0 & MTU 1514 bytes, BW 8000000 Kbit, DLY 5000 usec,
C=64.77+64.77+64.77+0.125≈194.3 系統R2到R5選下路徑cost值爲193，知道計算就OK
enable
conf t
no ip domain-lookup
exec-timeout 0 0
logging synch
exit
hostname
R2配置：
enable
conf t
interface S0/0
no shutdown
ip address 12.0.0.2 255.255.255.0
clock rate 64000
interface S0/1
no shutdown
ip address 24.0.0.2 255.255.255.0
clock rate 64000
exit
router ospf 100
network 12.0.0.0 0.0.0.255 area 0
network 24.0.0.0 0.0.0.255 area 0
R1配置：
enable
conf t
interface S0/0
no shutdown
ip address 12.0.0.1 255.255.255.0
clock rate 64000
interface S0/1
no shutdown
ip address 13.0.0.1 255.255.255.0
clock rate 64000
exit
router ospf 100
network 12.0.0.0 0.0.0.255 area 0
network 13.0.0.0 0.0.0.255 area 0
R3配置：
enable
conf t
interface S0/0
no shutdown
ip address 13.0.0.3 255.255.255.0
clock rate 64000
interface S0/1
no shutdown
ip address 35.0.0.3 255.255.255.0
clock rate 64000
exit
router ospf 100
network 13.0.0.0 0.0.0.255 area 0
network 35.0.0.0 0.0.0.255 area 0
R4配置:
enable
conf t
interface S0/0
no shutdown
ip address 24.0.0.4 255.255.255.0
clock rate 64000
interface e1/0
no shutdown
ip address 45.0.0.4 255.255.255.0
exit
router ospf 100
network 24.0.0.0 0.0.0.255 area 0
network 45.0.0.0 0.0.0.255 area 0
R5配置：
enable
conf t
interface S0/0
no shutdown
ip address 35.0.0.5 255.255.255.0
clock rate 64000
interface e1/0
no shutdown
ip address 45.0.0.5 255.255.255.0
interface loopback 0
ip address 5.5.5.5 255.255.255.255
no shutdown
exit
router ospf 100
network 13.0.0.0 0.0.0.255 area 0
network 35.0.0.0 0.0.0.255 area 0
network 5.5.5.5 0.0.0.0 area 0
以R2到R5的lookback0爲例，有兩條路徑，各路由cost值和小的爲R2選擇的路徑，所以要改變ospf的路徑，就要修改數據使cost值變化決定路徑走向
以直接修改cost值選路徑爲例：
cost值=各路由 （10^8）/BW相加
R2/R4/R5路由
s0/1* MTU 1500 bytes, BW 1544 Kbit, DLY 20000 usec,
e1/0* MTU 1500 bytes, BW 10000 Kbit, DLY 1000 usec,
loo0* MTU 1514 bytes, BW 8000000 Kbit, DLY 5000 usec,
10^8/(1544*1000)=64.77
10^8/(10000*1000)=10
10^8/(8000000*1000)=0.0125
C=64.77+10+0.0.125≈75
R2/R1/R3/R5路由
s0/0 & MTU 1500 bytes, BW 1544 Kbit, DLY 20000 usec,
s0/1 & MTU 1500 bytes, BW 1544 Kbit, DLY 20000 usec,
s0/1 & MTU 1500 bytes, BW 1544 Kbit, DLY 20000 usec,
loo0 & MTU 1514 bytes, BW 8000000 Kbit, DLY 5000 usec,
C=64.77+64.77+64.77+0.125≈194.3 系統R2到R5選下路徑cost值爲193，知道計算就OK