1. Routing With a Link-State Protocol
Introducing Routing and Switching in the Enterprise – Chapter 6

2. Objectives Describe and plan a network using OSPF.
Design and configure a network using single-area OSPF.
Work with multi-protocol environments.

3. Describe and Plan a Network Using OSPF
Link-state routing protocol
Open standard developed by IETF
Classless interior gateway protocol
Divides the network into areas for scalability

4. Describe and Plan a Network Using OSPF
Bandwidth determines the cost of a link
Higher bandwidth = lower cost = desirable route
Cost = 100,000,000 / bandwidth of link in bps
Manual cost configuration at an interface: ip ospf cost

5. Describe and Plan a Network Using OSPF
SPF algorithm (Diijkstra’s Algorithm)
Each router has a topological tree
SPF tree information stored in topology database

6. Describe and Plan a Network Using OSPF
Adjacencies: neighbor relationships
Hello protocol
Router ID
Role of loopback interfaces

7. Describe and Plan a Network Using OSPF
Designated router (DR)
Backup designated router (BDR)
DROther

8. Describe and Plan a Network Using OSPF
Area 0
Roles of routers in an OSPF Autonomous System:
Area Border Router (ABR)
Autonomous System Border Router (ASBR)

9. Design and Configure a Network Using Single-Area OSPF
OSPF configuration steps:
Enable OSPF + process ID
Advertise networks + wildcard mask and area ID

10. Design and Configure a Network Using Single-Area OSPF
Authentication protects integrity of routing information
Simple password authentication
Message Digest 5 (MD5)

11. Design and Configure a Network Using Single-Area OSPF
Tune OSPF parameters:
Interface priority
Router ID
Loopback and interface addresses
Bandwidth (cost )

12. Design and Configure a Network Using Single-Area OSPF
Verification and troubleshooting commands:
show ip ospf neighbor
show ip protocols, show ip route
show ip ospf, show ip ospf interface

13. Work with Multi-Protocol Environments
Default route configured on ASBR
ASBR distributes the route into the OSPF network

14. Work with Multi-Protocol Environments
Benefits of OSPF summarization:
Reduces number of networks advertised
Reduces memory requirements
Reduces number of entries in router updates
Isolates flapping and other problems to their location

15. Work with Multi-Protocol Environments
OSPF limitations:
Increased router memory and processing demands
Strict design requirements
Knowledgable administrator required
Initial discovery process takes up network bandwidth

16. Work with Multi-Protocol Environments
Administrative distance (AD) determines routes that appear in routing table

17. Summary
OSPF is a classless interior link-state routing protocol used in enterprise networks
OSPF uses bandwidth to generate the cost metric
OSPF routers elect a DR and BDR on multi-access networks
Router ID or router priority can be used to dictate the selection of DR and BDR
The OSPF network command uses a wildcard mask
Default route distribution and inter-area route summarization are used in OSPF networks