Cho sơ đồ như sau:

Các câu lệnh show:

show ip protocols

show ip ospf

show ip ospf interface

show ip ospf neighbor

show ip route

 

Cấu hình:

Nên cấu hình priority trước khi cấu hình OSPF!

Router có Priority cao nhất sẽ là DR, nhì là BDR, còn lại là DROther

- Default Priority là 1

- Router có Priority bằng nhau thì Router có Router-ID cao nhất là DR

Lưu ý: Priority=0 thì Router sẽ không tham gia bình bầu DR/BDR

Cách 1: Đổi priority

R1(config)#interface F0/1

R1(config-if)#ip ospf priority 100

R1(config-if)#end

R1# write

R2(config)#interface F0/1

R2(config-if)#ip ospf priority 50

R2(config-if)#end

R2# write

R3(config)#interface F0/1

R3(config-if)#ip ospf priority 1

R3(config-if)#end

R3# write

Cách 2: đổi Router-ID

router ospf 100

  router-id 211.1.1.1

  exit

Cách 3: Cấu hình Interface Loopback

Trên Switch:

Switch>en

Switch#conf t

Switch(config)#int range e0/0 - 2

Switch(config-if-range)#switchport

Switch(config-if-range)#end

Switch#write

 

Trên các router R1, R2, R3:

ip 192.168.1.11/24 192.168.1.1

ip 192.168.2.22/24 192.168.2.1

ip 192.168.3.33/24 192.168.3.1

en

conf t

hostname R1

int f0/0

no sh

ip add 192.168.1.1 255.255.255.0

exit

int f0/1

no sh

ip add 200.1.1.1 255.255.255.248

exit

do wr

en

conf t

hostname R2

int f0/0

no sh

ip add 192.168.2.1 255.255.255.0

exit

int f0/1

no sh

ip add 200.1.1.2 255.255.255.248

exit

do wr

en

conf t

hostname R3

int f0/0

no sh

ip add 192.168.3.1 255.255.255.0

exit

int f0/1

no sh

ip add 200.1.1.3 255.255.255.248

exit

do wr

 

Cấu hình OSPF:

router ospf 100

network 200.1.1.0 0.0.0.7 area 0

network 192.168.1.0 0.0.0.255 area 0

exit

do wr

router ospf 100

network 200.1.1.0 0.0.0.7 area 0

network 192.168.2.0 0.0.0.255 area 0

exit

do wr

router ospf 100

network 200.1.1.0 0.0.0.7 area 0

network 192.168.3.0 0.0.0.255 area 0

exit

do wr

Xem thông tin:

R1#show ip ospf neighbor

Neighbor ID Pri State Dead Time Address Interface

200.1.1.3 1 FULL/DROTHER 00:00:39 200.1.1.3 FastEthernet0/1

201.2.2.2 1 FULL/BDR 00:00:31 200.1.1.2 FastEthernet0/1

R1#

R2#show ip ospf neighbor

Neighbor ID Pri State Dead Time Address Interface

200.1.1.3 1 FULL/DROTHER 00:00:37 200.1.1.3 FastEthernet0/1

211.1.1.1 1 FULL/DR 00:00:37 200.1.1.1 FastEthernet0/1

R2#

R3#show ip ospf neighbor

Neighbor ID Pri State Dead Time Address Interface

201.2.2.2 1 FULL/BDR 00:00:36 200.1.1.2 FastEthernet0/1

211.1.1.1 1 FULL/DR 00:00:33 200.1.1.1 FastEthernet0/1

R3#

R1#show ip route

Codes: C - connected, S - static, R - RIP, M - mobile, B - BGP

D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area

N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2

E1 - OSPF external type 1, E2 - OSPF external type 2

i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2

ia - IS-IS inter area, * - candidate default, U - per-user static route

o - ODR, P - periodic downloaded static route

Gateway of last resort is not set

200.1.1.0/29 is subnetted, 1 subnets

C 200.1.1.0 is directly connected, FastEthernet0/1

C 192.168.1.0/24 is directly connected, FastEthernet0/0

O 192.168.2.0/24 [110/20] via 200.1.1.2, 00:02:44, FastEthernet0/1

O 192.168.3.0/24 [110/20] via 200.1.1.3, 00:02:44, FastEthernet0/1

R1#