OSPF OSPF Topics OSPF features OSPF areas OSPF

OSPF

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

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

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

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)

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

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

OSPF Metric 19. 2 kbps Source Destination – 10 to the 8 th/Bandwidth – Referred to as cost

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

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

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

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

OSPF Configuration Example E 0 172. 16. 1. 0 S 2 A 172. 16. 1. 1 10. 1. 1. 1 S 2 E 0 10. 1. 1. 2 C 192. 168. 1. 0 192. 168. 1. 1 router ospf 50 network 172. 16. 1. 1 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. 255. 0 area 0

Verifying the Routing Protocol —OSPF E 0 172. 16. 1. 0 S 2 A 172. 16. 1. 1 10. 1. 1. 1 S 2 10. 1. 1. 2 S 3 B S 3 E 0 C 10. 2. 2. 2 10. 2. 2. 3 192. 168. 1. 1 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 area 0 172. 16. 0. 0. 255 area 0 Routing Information Sources: Gateway Distance Last Update Distance: (default is 110) 192. 168. 1. 0

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

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