OSPF Kevin Piper, David Perry, Tom Hoffman, Emely Pagan Valencia Community College Cisco Networking
Agenda • OSPF overview • Configuring single area OSPF lab • Router designation • Configuring multi-area OSPF lab • Verifying and managing OSPF • Questions or comments Valencia Community College Cisco Networking
Overview • OSPF (open shortest path first). • A link state protocol. Link state protocols use the shortest path first algorithm to populate the routing table. OSPF shares information with every router on the network. • OSPF and Cisco. • OSPF is nonproprietary to Cisco. • Developed 1988 by internet engineering task force (IETF). • Developed to be a interior gateway protocol. • Used by routers in the same autonomous system. Valencia Community College Cisco Networking
OSPF Terms Valencia Community College Cisco Networking
Configuring Cost Cost 64.7 Cost 64.7 1.544MB R4 1.544MB R3 R5 Cost 1 Cost =1562 Cost =195.1 100MB 56KB Cost 1562 R1 1.544MB R2 Cost 64.7 Cost = 10^8 / bandwidth Valencia Community College Cisco Networking
Advantages Supports VLSM Faster convergence Efficient bandwidth utilization No hop-count limit Path selection based on cost Loop-free routing environment Disadvantages Difficult to configure More time to plan CPU/memory intensive Pros and Cons Valencia Community College Cisco Networking
Considerations • Size of the area • Number of neighbors per router • Problem isolation • Restriction of routing information • Stable backbone design • Addressing areas Valencia Community College Cisco Networking
Length 1 byte 1 byte 2 bytes 4 bytes 4 bytes 2 bytes 2 bytes 8bytes Version Number Authentication type Packet Length Router ID Description Type Area ID Check sum Authentication 24 bytes 4 bytes 2 bytes 1 byte 1 byte 4 bytes 4 bytes 4 bytes 4 bytes each Length OSPF Packet Header Backup designated router Hello interval option Router Priority Dead interval Designated router Additional Neighbor Description Netmask OSPF packet header Hello Packet Valencia Community College Cisco Networking
Forming Adjacencies • Init state • Establish bi-directional communication • Exstart • Exchange state • Loading state • Full state Valencia Community College Cisco Networking
Router Adjacencies Without Designated Routers R1 R2 R6 R3 R5 R4 15 Router adjacencies Valencia Community College Cisco Networking
Router Designation • Election process • Hello Packet • Priority • Designated router (DR) • Backup DR (BDR) • DR other Valencia Community College Cisco Networking
Router Adjacencies With Designated Routers R1 R2 R6 R3 R5 BDR 9 Router adjacencies R4 DR Valencia Community College Cisco Networking
Configuring Single Area OSPF Valencia Community College Cisco Networking
Single Area OSPF Layout Area 1 131.108.1.2/24 131.108.1.1/24 R3’s Loopback R3’s Loopback Router 1 E0 Loopback0 11.11.11.11 E0 Loopback0 22.22.22.22 Switch Router 2 E0 131.108.1.3/24 Router 3 R3’s Loopback Loopback0 33.33.33.33 Valencia Community College Cisco Networking
Configuration Files Router 1 Router 2 Router 3 Valencia Community College Cisco Networking
Configuring Multi-area OSPF • Why use multi-area OSPF ? • Advantages • Smaller routing tables • Less routing update overhead • Faster synchronization • Disadvantages • Complex to implement Valencia Community College Cisco Networking
OSPF Router Types • Internal • Area border router (ABR) • Autonomous systems border router (ASBR) • Backbone router Valencia Community College Cisco Networking
Multi-area OSPF Layout Switch 131.108.1.2/24 131.108.1.1/24 Area 1 E0 Router 1 E0 Router 2 S0 Area 2 141.108.10.0/30 S1 141.108.10.4/38 Router 3 S1 S0 E0 E0 131.108.26.1/24 131.108.33.1/24 Router 4 Area 0 Valencia Community College Cisco Networking
Router 1 configuration Valencia Community College Cisco Networking
Router 2 configuration Valencia Community College Cisco Networking
Router 3 Configuration Valencia Community College Cisco Networking
Router 4 configuration Valencia Community College Cisco Networking
Verifying and Managing OSPF • OSPF process • OSPF neighbors • Interface configuration • Link states • Timers • Debugging Valencia Community College Cisco Networking
Issues • Redistributing ANYTHING into OSPF Redistributing OSPF 1 Valencia Community College Cisco Networking
Issues • Lab closing on 14:00 on Friday. • No lab hours on weekends. Valencia Community College Cisco Networking
