OSPF RoutingCollected By: Mehdi DaneshvarSupervisor: E.M.Kosari

Router

Routing

Routing Protocols

StaticDynamic

Dynamic RoutingPath DeterminationMetricsConvergenceLoad Balancing

Dynamic Routing Protocols

IGP – Interior Gateway ProtocolEGP – Exterior Gateway Protocol

Dynamic Routing ProtocolsDistance Vector Protocols

RIP, IGRPLink State Protocols

OSPF, IS-ISPath Vector Protocols

BGP

OSPF

OSPF NetworkBroadcast NetworkPoint-to-Point NetworkNon-Broadcast Multi-Access (NBMA)Point-to-MultipointVirtual Links

Multi AccessDesignated Router-DRBackup Designated Router-BDRDROTHER

OSPF Designated Router Optimizing LSA flooding Process on multi-access links DR represent the multi-access network (by LSA2) and adjacency

with others. Selection of DR is per interface. DR election : Higher priority (1-255) + higher RID Priority of 0 means no intention to become the DR or BDR DRothers send update packets to the AllDRouters (224.0.0.6) All routers continue to multicast Hellos to the ALLSPFRouthers

(244.0.0.5) DR floods the updates to ALLSPFRouters (244.0.0.5)

OSPF PACKET TYPESHello : Neighbor Discovery/MaintenanceDBD : Database DescriptionLSR : Database Download RequestLSU : Database UpdateLSAck : Flooding Acknowledgement

Hello Packet

OSPF Finite State MachineDownAttempt (only on NBMA) Init – Hello is seen2-Way – own RID is seen in Hello from neighborExStart – Master/Slave relation (highest RID) Slave sets

MS-bit=0Exchange – Database Description LSRsLoading – Transfer LSAs (LSR, LSU, LSAck)Full – Adjacent

Neighbor State

Neighbor Timers

Fast Timer : Hello 10, Dead 40Slow Timer : Hello 30, Dead 120

OSPF Router ID

Each router OSPF router must have unique identifier = Router ID

Router ID and LSA Sequence number are used to detect duplicate LSAs

Router ID is highest IP address from any operational interface

OSPF NeighborsArea ID and Area TypeAuthenticationNetwork Mask (Not P2P link)Hello Interval Router Dead IntervalOptionMTU

OSPF LSA Types Router Link State – Type 1 Network Link State – Type 2 Summery Link State – Type 3 Summery ASBR Link State – Type 4 AS External Network Link State – Type 5 NSSA External Network Link State – Type 7

OSPF AREAS Area 0 = Backbone Area Area x = non-transit flooding domain Stub Area = External routers are not flooded but internal

summaries are. Totally Stubby Area = All Routers receive a default route only

from ABR. Not-So-Stubby Area (NSSA) = External connection to another AS

is permitted.

The routers in Area Internal RouterBackbone RouterABRASBR

OSPF PerformancingRouters in the area : Max = 50Router Neighbors : Max = 60ABRs in the area : Max=3Select one fast speed Interface for DR or BDR.

OSPF Virtual LinkAllowing traffic to traverse from the backbone area to pas

through another area.Must be configured between two ABRs.Transit are must have full routing table an cannot be a stub

area.

OSPF SummaryDeveloped by OSPF working group at IETFClassified as an IGPUses IP Protocol 89Dijkstra Algorithm to calculate SPFMetric Cost (per interface)ALLSPFRouters : 224.0.0.5ALLDRouters 224.0.0.6Default OSPF R Priority : 1Full LSDB topology sync first , then partial LSA flooding.VLSM and Route tags are supported.Summarization at Area boundray.

OSPF vs. RIPOSPF

Select Best Path Traffic Type of Service

Hierarchical RoutingSender's Routing Table Authentication

Example Scenario

Example ScenarioNet A to Net B:

Send 1, 2, 4, 6, 7, 5, 3Recive 3,2,1

Resources1. RFC 23282. Wikipedia : http://en.wikipedia.com/ospf3. OSPF : http://www.shafagh.com/4. EIGRP & OSPF: http://www.shafagh.com/ 5. Forums of Cisco in persian: http://www.ciscoinpersian.com/ 6. Mohsen zoleh, BA Thesis : http://www.prozhe.com

Any question?