OSPF Kevin Piper David Perry Tom Hoffman Emely

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 Designated Router (DR) Backup DR Priority Autonomous System (AS) Area Border Router (ABR) Link State advertisement (LSA) Router ID Topology Table Adjacency Link state Area Cost Valencia Community College Cisco Networking

Configuring Cost 64. 7 1. 544 MB Cost 64. 7 R 4 1. 544 MB R 3 R 5 Cost 1 100 MB Cost =195. 1 Cost =1562 56 KB Cost 1562 R 2 1. 544 MB R 1 Cost 64. 7 Cost = 10^8 / bandwidth Valencia Community College Cisco Networking

Pros and Cons • Advantages • Disadvantages – Supports VLSM – Faster convergence – Efficient bandwidth utilization – No hop-count limit – Path selection based on cost – Loop-free routing environment – Difficult to configure – More time to plan – CPU/memory intensive 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

OSPF packet header Length Description 1 byte Version Number Type 2 bytes Packet Length 4 bytes Router ID 4 bytes 2 bytes Area ID Check sum 2 bytes 8 bytes Authentication type Authentication Hello Packet Length Description 24 bytes OSPF Packet Header 4 bytes 2 bytes Netmask Hello interval 1 byte option 1 byte 4 bytes Router Priority Dead Designated interval router Valencia Community College Cisco Networking 4 bytes Backup designated router 4 bytes each Additional Neighbor

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 R 1 R 6 R 2 R 5 R 3 R 4 Valencia Community College Cisco Networking 15 Router adjacencies

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 R 1 R 6 R 2 R 5 R 3 BDR 9 Router adjacencies R 4 DR Valencia Community College Cisco Networking

Configuring Single Area OSPF Valencia Community College Cisco Networking

Single Area OSPF Layout Area 1 131. 108. 1. 1/24 R 3’s Loopback 0 11. 11. 11 Router 1 E 0 Switch E 0 131. 108. 1. 2/24 E 0 Router 2 131. 108. 1. 3/24 Router 3 R 3’s Loopback 0 33. 33. 33 Valencia Community College Cisco Networking R 3’s Loopback 0 22. 22. 22

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. 1/24 Router 1 131. 108. 1. 2/24 Area 1 E 0 Router 2 S 0 Area 2 141. 108. 10. 0/30 S 1 141. 108. 10. 4/38 131. 108. 33. 1/24 E 0 Router 4 S 1 Router 3 S 0 Area 0 Valencia Community College Cisco Networking E 0 131. 108. 26. 1/24

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