CCNA 4-7 OSPF.ppt

? 2007 Cisco Systems, Inc. All rights reserved. ICND2 — 4-1 Single-Area OSPF Implementation Implementing OSPF ? 2007 Cisco Systems, Inc. All rights reserved. ICND2 — 4-2 OSPF Overview ? Creates a neighbor relationship by exchanging hello packets ? Propagates LSAs rather than routing table updates – Link: Router interface – State: Description of an interface and its relationship to neighboring routers ? Floods LSAs to all OSPF routers in the area, not just directly connected routers ? Pieces together all the LSAs generated by the OSPF routers to create the OSPF link-state database ? Uses the SPF algorithm to calculate the shortest path to each destination and places it in the routing table ? 2007 Cisco Systems, Inc. All rights reserved. ICND2 — 4-3 OSPF Hierarchy Example ? Minimizes routing table entries ? Localizes the impact of a topology change within an area ? 2007 Cisco Systems, Inc. All rights reserved. ICND2 — 4-4 Neighbor Adjacencies: The Hello Packet ? 2007 Cisco Systems, Inc. All rights reserved. ICND2 — 4-5 SPF Algorithm ? Places each router at the root of a tree and calculates the shortest path to each destination based on the cumulative cost ? Cost = Reference Bandwidth / Interface Bandwidth ( b/s ) 101 101 1 ? 2007 Cisco Systems, Inc. All rights reserved. ICND2 — 4-6 Configuring Single-Area work address wildcard-mask area area-id ? works to a specific OSPF area router ospf process-id ? Defines OSPF as the IP routing protocol RouterX(config)# RouterX(config-router)# ? 2007 Cisco Systems, Inc. All rights reserved. ICND2 — 4-7 Configuring Loopback Interfaces Router ID: ? Number by which the router is known to OSPF ? Default: The highest IP address on an active interface at the moment of OSPF process startup ? Can be overridden by a loopback interface: Highest IP address of any active loopback interface ? Can be set manually using the router-id command ? 2007 Cisco Systems, Inc. All rights reserve