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Lecture #3 OSPF
Asst.Prof. Dr.Anan Phonphoem
Department of Computer Engineering,
Faculty of Engineering, Kasetsart University,
Bangkok, Thailand
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Outline
Distance VS. Link-State Route selection Link-State network (OSPF) Link-State Operation Basic OSPF configuration and verification
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Distance Vector VS. Link-State
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Pro/Con of Link-State
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Route Selection
RIP
OSPF
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Multiple-Area
OSPF Network
Single-Area
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Terminology
•Link•Link-State•Link-State db•Area•Cost•Routing Table•Adjacency db•DR / BDR
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OSPF path cost
Cisco Default Value
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OSPF Packet Header
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Concept of link state routing
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Cost (weight) in link state routing
Cost is applied only by routerCost is applied when packet leaves the router
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Link state packet
Cost: weight (traffic, security level, link state)
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Flooding of A’s LSP
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Link state database
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Shortest path tree
Build the tree, start by identifying a root
attach all reached nodes Compare arcs and find the lowest cost
add this node (to be permanent) and
its arcs (temp) Examine database and identify the reachable node Repeat the last two steps
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Costs in the Dijkstra algorithm
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Shortest path calculation
Step1 Step2
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Shortest path calculation
Step3 Step4
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Shortest path calculation
Step5 Step6
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Shortest path calculation – S7
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Shortest path calculation – S8
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Shortest path calculation – S9
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Shortest path calculation – S10
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Shortest path calculation – S11
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Shortest path calculation – S12
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Shortest path calculation – S13
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Link state routing table for router A
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Basic configuration
•Wildcard-Mask•Area ID
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Basic configuration - Loopback
Setup Loopback Ensure that at least one is active (For stability)
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Basic configuration - priority
Setup priority For DR/BDR selection
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OSPF verification
show ip protocol show ip route
show ip ospf show ip ospf interface
show ip ospf database
show ip ospf neighbor detail
clear ip route * clear ip route a.b.c.d
debug ip ospf events debug ip ospf adj