Lecture #3 OSPF

Asst.Prof. Dr.Anan Phonphoem

Department of Computer Engineering,

Faculty of Engineering, Kasetsart University,

Bangkok, Thailand

Outline

Distance VS. Link-State Route selection Link-State network (OSPF) Link-State Operation Basic OSPF configuration and verification

Distance Vector VS. Link-State

Pro/Con of Link-State

Route Selection

RIP

OSPF

Multiple-Area

OSPF Network

Single-Area

Terminology

•Link•Link-State•Link-State db•Area•Cost•Routing Table•Adjacency db•DR / BDR

OSPF path cost

Cisco Default Value

OSPF Packet Header

Concept of link state routing

Cost (weight) in link state routing

Cost is applied only by routerCost is applied when packet leaves the router

Link state packet

Cost: weight (traffic, security level, link state)

Flooding of A’s LSP

Link state database

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

Costs in the Dijkstra algorithm

Shortest path calculation

Step1 Step2

Shortest path calculation

Step3 Step4

Shortest path calculation

Step5 Step6

Shortest path calculation – S7

Shortest path calculation – S8

Shortest path calculation – S9

Shortest path calculation – S10

Shortest path calculation – S11

Shortest path calculation – S12

Shortest path calculation – S13

Link state routing table for router A

Basic configuration

•Wildcard-Mask•Area ID

Basic configuration - Loopback

Setup Loopback Ensure that at least one is active (For stability)

Basic configuration - priority

Setup priority For DR/BDR selection

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