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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?