OSPF (Open Shortest Path First) OSPF Protocols

1
OSPF (Open Shortest Path First)

• ?????
• ?? ???

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OSPF Protocols and Operation

• Neighbor???????
• Database exchange??????
• Route calculation??????

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OSPF Neighbors 1/3

• OSPF Neighbors????data link,?????OSPF???????????
• OSPF Router ID (RID)????router?32????,???IP
• Hello message
• ?IP????protocol type ?89
• ??multicast address 224.0.0.5

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OSPF Neighbors 2/3

• Hello packet??
• RID, Area ID, Hello interval, dead interval,
  router priority, DR?RID, BDR?RID, ???neighbor??
• ?Hello?????????,?????neighbor

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OSPF Neighbors 3/3
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OSPF Topology Database Exchange

• ??Topology Database??
• ???????????DR, BDR
• ?????LSDB????,?????Fully adjacent
• ???,??FULL???????????reflood LSA

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Choosing a Designated Router (DR) 1/
Point-to-point????DR Broadcast???DR
router??DR??topology database ??DR?????router
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Choosing a Designated Router (DR) 2/

• ??DR???
• ??OSPF priority(1255)??DR
• ?priority??,?RID????DR
• ????BDR
• ??OSPF priority??0,??????
• ????DR, BDR,?????router?????

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Choosing a Designated Router (DR) 3/

• OSPF priority
• RID
• loopback interface?IP???
• ??lo,??????IP????

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Building the IP Routing Table

• OSPF???????neighbor table
• OSPF???????topology table
• OSPF??Dijkstra SPF ???,?topology
  table???????????,??routing table,

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???OSPF??
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OSPF Area 1/2

• OSPF???????????
• ???topology database???????
• SPF?????????,????????????
• ??router???(up/down)??,????router????SPF??

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OSPF Area 2/2

• OSPF Area????????

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OSPF???

• ????
• Router ospf 1
• Network 10.0.0.0 0.255.255.255 area 0
• CISCO?108/?????cost
• 100Mbps???????cost?1
• 64,000bps?cost?1563
• OSPF????16?equal-cost??