Ospf(MA)
一.選擇DR/BDR
二.在選出DR/BDR之後,修改BDR/DROTHER優先級,是否能夠搶佔DR
三.在選出DR/BDR之後,將DROTHER優先級改最高,當DRdown後,是否BDR或DROTHER最成爲DR。
一.搭建拓撲:
R1:
R1(config)#intethernet0/0
R1(config-if)#ipadd110.1.1.1255.255.255.0
R1(config-if)#intlo0
R1(config-if)#ipadd1.1.1.1255.255.255.0
R1(config)#routeros110
R1(config-router)#router-id1.1.1.1
R1(config-router)#network110.1.1.00.0.0.255area0
R1(config-router)#network1.1.1.00.0.0.255area0
R2:
R2(config)#intethernet0/0
R2(config-if)#ipadd110.1.1.2255.255.255.0
R2(config-if)#intlo0
R2(config-if)#ipadd2.2.2.2255.255.255.0
R2(config)#routeros110
R2(config-router)#router-id2.2.2.2
R2(config-router)#network110.1.1.00.0.0.255area0
R2(config-router)#network2.2.2.00.0.0.255area0
R3:
R3(config)#intethernet0/0
R3(config-if)#ipadd110.1.1.3255.255.255.0
R3(config-if)#intlo0
R3(config-if)#ipadd3.3.3.3255.255.255.0
R3(config)#routeros110
R3(config-router)#router-id3.3.3.3
R3(config-router)#network110.1.1.00.0.0.255area0
R3(config-router)#network3.3.3.00.0.0.255area0
R1查看鄰居表:
R1#shiposnei
NeighborIDPriStateDeadTimeAddressInterface
2.2.2.21FULL/BDR00:00:35110.1.1.2Ethernet0/0
3.3.3.31FULL/DR00:00:39110.1.1.3Ethernet0/0
R2查看鄰居表:
R2#shiposnei
NeighborIDPriStateDeadTimeAddressInterface
1.1.1.11FULL/DROTHER00:00:36110.1.1.1Ethernet0/0
3.3.3.31FULL/DR00:00:38110.1.1.3Ethernet0/0
注:R1/R2/R3優先級默認都爲1routerid大將成爲DR,其次BDR。
-------------------------------------------------------------------------------
二.在R2上ethernet0/0上修改優先級爲“5”
R2#shiposintethernet0/0
Ethernet0/0isup,lineprotocolisup
InternetAddress110.1.1.2/24,Area0
ProcessID110,RouterID2.2.2.2,NetworkTypeBROADCAST,Cost:10
TransmitDelayis1sec,StateBDR,Priority1
DesignatedRouter(ID)3.3.3.3,Interfaceaddress110.1.1.3
在接口上修改:
R2(config)#intethernet0/0
R2(config-if)#ipospriority5
R2#shiposinterfaceethernet0/0
Ethernet0/0isup,lineprotocolisup
InternetAddress110.1.1.2/24,Area0
ProcessID110,RouterID2.2.2.2,NetworkTypeBROADCAST,Cost:10
TransmitDelayis1sec,StateBDR,Priority5
DesignatedRouter(ID)3.3.3.3,Interfaceaddress110.1.1.3
在R1或R3上查看鄰居表:
R1#shiposnei
NeighborIDPriStateDeadTimeAddressInterface
2.2.2.25FULL/BDR00:00:31110.1.1.2Ethernet0/0
3.3.3.31FULL/DR00:00:35110.1.1.3Ethernet0/0
注:1.修改R2接口優先級後,不搶佔DR。(不具有搶佔性)重建鄰居後,重新選舉,R2才能成爲DR
2.選DR取決於兩個因素,優先級和routerid,都是越大越優,優先級更勝routerid,優先級一致再比較routerid大小。
三.把R1優先級修改爲“7”在R1/R2/R3中R1(DROTHER)優先級最高,把R2優先級還原默認“1”
R2還原默認優先級:
R2(config)#intethernet0/0
R2(config-if)#noipospriority
R2#shiposintethernet0/0
Ethernet0/0isup,lineprotocolisup
InternetAddress110.1.1.2/24,Area0
ProcessID110,RouterID2.2.2.2,NetworkTypeBROADCAST,Cost:10
TransmitDelayis1sec,StateBDR,Priority1
DesignatedRouter(ID)3.3.3.3,Interfaceaddress110.1.1.3
R1優先級改爲“7”
R1(config)#intethernet0/0
R1(config-if)#ipospriority7
R1#shiposinterfaceethernet0/0
Ethernet0/0isup,lineprotocolisup
InternetAddress110.1.1.1/24,Area0
ProcessID110,RouterID1.1.1.1,NetworkTypeBROADCAST,Cost:10
TransmitDelayis1sec,StateDROTHER,Priority7
DesignatedRouter(ID)3.3.3.3,Interfaceaddress110.1.1.3
R3查看鄰居表:
R3#shiposnei
NeighborIDPriStateDeadTimeAddressInterface
1.1.1.17FULL/DROTHER00:00:34110.1.1.1Ethernet0/0
2.2.2.21FULL/BDR00:00:33110.1.1.2Ethernet0/0
將R3的ethernet0/0置down狀態。
R3(config)#intethernet0/0
R3(config-if)#sh
分別在R1和R2查看鄰居表信息:
R1#shiposnei
NeighborIDPriStateDeadTimeAddressInterface
2.2.2.21FULL/DR00:00:35110.1.1.2Ethernet0/0
R2#shiposnei
NeighborIDPriStateDeadTimeAddressInterface
1.1.1.17FULL/BDR00:00:36110.1.1.1Ethernet0/0
注:原來R2(BDR)成爲DR優先級爲“1”,R1(DROTHER)成爲BDR。優先級爲“7”.
當DRdown後,優選BDR升爲DR,和優先級無關。