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OSPF · P ART 1 - PacketLife.net

Jeremy PART1 Protocol HeaderTypeAttributesAlgorithmMetricLink- StateDijkstraCost (Bandwidth)ADStandardProtocolsTransport1 10 RFC 2328, 2740 IPIP/89 Router TypesInternal RouterAll interfaces reside within the same areaBackbone RouterA router with an interface in area 0 (the backbone)Area Border Router (ABR)Connects two or more areasAS Boundary Router (ASBR)Connects to additional routing domains; typically located in the backboneTroubleshootingshow ip [route | protocols]show ip ospf interfaceshow ip ospf neighbor* modifiable withospf auto-cost reference-bandwidthMetric FormulaVersionTypeLength8162432 Router IDArea IDChecksumInstance IDReservedDataLink State AdvertisementsRouter Link (Type 1)Lists neighboring routers and the cost to each; flooded within an areaNetwork Link (Type 2)Generated by a DR; lists all routers on an adjacent segment; flooded within an areaNetwork Summary (Type 3)Generated by an ABR and advertised among areasASBR Summary (Type 4)Injected by an ABR into the backbone to advertise the presence of an ASBR within an areaExternal Link (Type 5)Generated by

packetlife.net by Jeremy Stretch v2.1 OSPF · P ART 1 Protocol Header Type Attributes Algorithm Metric Link-State Dijkstra Cost (Bandwidth) AD Standard Protocols

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Transcription of OSPF · P ART 1 - PacketLife.net

1 Jeremy PART1 Protocol HeaderTypeAttributesAlgorithmMetricLink- StateDijkstraCost (Bandwidth)ADStandardProtocolsTransport1 10 RFC 2328, 2740 IPIP/89 Router TypesInternal RouterAll interfaces reside within the same areaBackbone RouterA router with an interface in area 0 (the backbone)Area Border Router (ABR)Connects two or more areasAS Boundary Router (ASBR)Connects to additional routing domains; typically located in the backboneTroubleshootingshow ip [route | protocols]show ip ospf interfaceshow ip ospf neighbor* modifiable withospf auto-cost reference-bandwidthMetric FormulaVersionTypeLength8162432 Router IDArea IDChecksumInstance IDReservedDataLink State AdvertisementsRouter Link (Type 1)Lists neighboring routers and the cost to each; flooded within an areaNetwork Link (Type 2)Generated by a DR; lists all routers on an adjacent segment.

2 Flooded within an areaNetwork Summary (Type 3)Generated by an ABR and advertised among areasASBR Summary (Type 4)Injected by an ABR into the backbone to advertise the presence of an ASBR within an areaExternal Link (Type 5)Generated by an ASBR and flooded throughout the AS to advertise a route external to OSPFNSSA External Link (Type 7)Generated by an ASBR in a not-so-stubby area; converted into a type 5 LSA by the ABR when leaving the areaDR/BDR Election The BDR also maintains adjacencies with all routers in case the DR fails Election does not occur on point-to-point or multipoint links Default priority (0-255) is 1; highest priority wins; 0 cannot be elected DR preemption will not occur unless the current DR is resetVirtual Links Tunnel formed to join two areas across an intermediate Both end routers must share a common area At least one end must reside in area 0 Cannot traverse stub areasArea TypesStandard AreaDefault OSPF area typeStub AreaExternal link (type 5) LSAs are replaced with a default routeTotally Stubby AreaType 3, 4, and 5 LSAs are replaced with a default routeNot So Stubby Area (NSSA)A stub area containing an ASBR.

3 Type 5 LSAs are converted to type 7 within the areaExternal Route TypesE1 Cost to the advertising ASBR plus the external cost of the routeE2 (Default) Cost of the route as seen by the ASBRA uthenticationAllSPF AddressAllDR AddressPlaintext, States12 DownAttempt56 ExstartExchange34 Init2-Way78 LoadingFullshow ip ospf border-routersshow ip ospf virtual-linksdebug ip ospf [..]cost = 100,000 Kbps*link speed The DR serves as a common point for all adjacencies on a multiaccess Jeremy PART2 Configuration Exampleinterface Serial0/0description WAN Linkip address !interface FastEthernet0/0description Area 0ip address !interface Loopback0! Used as router IDip address !router ospf 100! Advertising the WAN cloud to OSPF redistribute static subnetsnetwork area 0!

4 ! Static route to the WAN cloudip route Ethernet0/0description Area 9ip address ospf 100 area 9!interface Ethernet0/1description Area 2ip address ospf 100 area 2! Optional MD5 authentication configuredip ospf authentication message-digestip ospf message-digest-key 1 md5 FooBar! Give C second priority (BDR) in electionip ospf priority 50!!!!!!interface Loopback0ip address !router ospf 100! Define area 9 as a totally stubby areaarea 9 stub no-summary! Virtual link from area 9 to area 0area 2 virtual-link Ethernet0/0description Area 0ip address ospf 100 area 0!interface Ethernet0/1description Area 2ip address ospf 100 area 2! Optional MD5 authentication configuredip ospf authentication message-digestip ospf message-digest-key 1 md5 FooBar!

5 Give B priority in DR electionip ospf priority 100!interface Ethernet0/2description Area 1ip address ospf 100 area 1!interface Loopback0ip address !router ospf 100! Define area 1 as a stub areaarea 1 stub! Virtual link from area 0 to area 9area 2 virtual-link ARouter CRouter BNetwork TypesDR/BDR ElectedNonbroadcast (NBMA)Multipoint BroadcastNeighbor DiscoveryHello/Dead TimersDefined BySupported TopologyMultipoint NonbroadcastBroadcastPoint-to-PointYesNo 30/120 RFC 2328 Full MeshNoYes30/120 RFC 2328 AnyNoNo30/120 CiscoAnyYesYes10/40 CiscoFull MeshNoYes10/40 CiscoPoint-to-PointArea 0 ABackboneArea 9 Totally Stubby AreaArea 1 Stub AreaArea 2 Standard


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