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OSPF

Learn about OSPF features like fast convergence and granular metric, understanding OSPF areas, operation, LSAs, metric, and load balancing. Configure OSPF and verify routing.

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OSPF

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  1. OSPF

  2. OSPF Topics • OSPF features • OSPF areas • OSPF operation • OSPF on multi-access broadcast networks • OSPF LSAs • OSPF metric • OSPF load balancing • OSPF configuration • OSPF authentication

  3. OSPF Features • Fast convergence • Granular metric • Supports VLSM • Hierarchical design/route summarization • Uses multicasts • Supports authentication

  4. OSPF Overview • Link State Routing Protocol • Router advertises the state of it’s links (connections to networks) • Forms neighbor relationships (adjacencies) before exchanging routing information • Neighbor information maintained in neighbor table • Advertisements flooded within area

  5. OSPF Areas • Areas restrict certain advertisements so that in a large environment not all advertisements flooded everywhere • Every AS should have an area 0 - Backbone • All other areas connect to Backbone • Summarization can be configured at area borders – further reduces advertisements • Router with interfaces in two or more areas is Area Border Router (ABR)

  6. OSPF Operation • First forms adjacencies • requires that certain criteria be met • Floods LSAs • sent to 224.0.0.5 • collected in LSA database • Calculates shortest routes - Dykstra • Maintains adjacencies with hellos • Sends updates only when changes occur

  7. OSPF LSAs • LSA Type 1 – • sent by every router • advertises it’s OSPF interfaces • LSA Type 2 – • sent by DR • contains a list of all routers on subnet • LSA Type 3 – • sent by ABR into other areas • advertises area networks and metrics

  8. 10 to the 8th/Bandwidth Referred to as cost OSPF Metric 19.2 kbps 19.2 kbps Source Destination

  9. Maximum six equal paths – default 4 equal paths OSPF Load Balancing New Route Source Initial Route Destination

  10. OSPF Operation Multi-access network • Designated Router first determined • First router active becomes DR • Second router active becomes BDR • All others become ODR • If DR goes down, BDR becomes DR and new BDR elected • Router with highest priority wins. If tied, • Router with highest OSPF Router ID

  11. OSPF Priority and RID • OSPF priority set on per-interface basis • default priority is 1 • command is “ip ospf priority <number>” • priority of 0 means can’t become DR • OSPF Router ID – set 3 possible ways • Router ID command. If not set then - • Highest loopback address. If not set then – • Highest active IP address

  12. Configuring OSPF Router(config)#router ospf process-id • Defines OSPF as the IP routing protocol network network-number wild-card-mask area-id • Selects participating attached networks

  13. OSPF Configuration Example E0 S2 S2 E0 192.168.1.0 172.16.1.0 A C 10.1.1.1 172.16.1.1 10.1.1.2 192.168.1.1 router ospf 50 network 172.16.1.1 0.0.0.0 area 0 network 10.1.1.0 0.0.0.255 area 0 router ospf 75 network 192.168.1.0 0.0.0.255 area 0 network 10.0.0.0 0.255.255.255.0 area 0

  14. Verifying the Routing Protocol—OSPF E0 S2 S2 S3 S3 E0 192.168.1.0 172.16.1.0 A B C 10.1.1.1 172.16.1.1 10.1.1.2 10.2.2.2 192.168.1.1 10.2.2.3 Routing Protocol is "ospf 1" Outgoing update filter list for all interfaces is not set Incoming update filter list for all interfaces is not set Router ID 172.16.1.1 Number of areas in this router is 1. 1 normal 0 stub 0 nssa Maximum path: 4 Routing for Networks: 10.1.1.1 0.0.0.0 area 0 172.16.0.0 0.0.255.255 area 0 Routing Information Sources: Gateway Distance Last Update Distance: (default is 110)

  15. OSPF Show Commands • show ip route ospf • show ip ospf interfaces • show ip ospf neighbors • show ip ospf database

  16. Lab Lab files OSPF Configuration Lab-1.doc OSPF Configuration Lab-2.doc Lab scenarios OSPF Configuration Lab-1.pkt OSPF Configuration Lab-2.pkt

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