1. Kevin Piper, David Perry, Tom Hoffman, Emely Pagan
OSPF
Kevin Piper, David Perry, Tom Hoffman, Emely Pagan
6/1/2018
Valencia Community College
Cisco Networking

2. Valencia Community College
Agenda
OSPF overview
Configuring single area OSPF lab
Router designation
Configuring multi-area OSPF lab
Verifying and managing OSPF
Questions or comments
6/1/2018
Valencia Community College
Cisco Networking

3. Valencia Community College
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.
6/1/2018
Valencia Community College
Cisco Networking

4. Valencia Community College
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
6/1/2018
Valencia Community College
Cisco Networking

5. Valencia Community College
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
6/1/2018
Valencia Community College
Cisco Networking

6. Valencia Community College
Pros and Cons
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
6/1/2018
Valencia Community College
Cisco Networking

7. Valencia Community College
Considerations
Size of the area
Number of neighbors per router
Problem isolation
Restriction of routing information
Stable backbone design
Addressing areas
6/1/2018
Valencia Community College
Cisco Networking

8. OSPF packet header Hello Packet 6/1/2018 Valencia Community College
Authentication
Length
Description
8bytes
Packet Length
Type
4 bytes
1 byte
Version Number
2 bytes
Authentication type
Check sum
Area ID
Router ID
Hello Packet
Additional Neighbor
Length
Description
4 bytes each
Hello interval
Netmask
1 byte
24 bytes
OSPF Packet Header
2 bytes
4 bytes
Designated router
Backup designated router
Dead interval
Router Priority
option
6/1/2018
Valencia Community College
Cisco Networking

9. Valencia Community College
Forming Adjacencies
Init state
Establish bi-directional communication
Exstart
Exchange state
Loading state
Full state
6/1/2018
Valencia Community College
Cisco Networking

10. Router Adjacencies Without Designated Routers
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Valencia Community College
Cisco Networking

11. Valencia Community College
Router Designation
Election process
Hello Packet
Priority
Designated router (DR)
Backup DR (BDR)
DR other
6/1/2018
Valencia Community College
Cisco Networking

12. Router Adjacencies With Designated Routers
BDR
9 Router adjacencies R4 DR
6/1/2018
Valencia Community College
Cisco Networking

13. Configuring Single Area OSPF
6/1/2018
Valencia Community College
Cisco Networking

14. Single Area OSPF Layout
/24
/24
R3’s Loopback
R3’s Loopback
Router 1 E0
Loopback E0
Loopback
Switch
Router 2 E0
/24
Router 3
R3’s Loopback
Loopback
6/1/2018
Valencia Community College
Cisco Networking

15. Valencia Community College
Configuration Files
Router 1
Router 2
Router 3
6/1/2018
Valencia Community College
Cisco Networking

16. Configuring Multi-area OSPF
Why use multi-area OSPF ?
Advantages
Smaller routing tables
Less routing update overhead
Faster synchronization
Disadvantages
Complex to implement
6/1/2018
Valencia Community College
Cisco Networking

17. Valencia Community College
OSPF Router Types
Internal
Area border router (ABR)
Autonomous systems border router (ASBR)
Backbone router
6/1/2018
Valencia Community College
Cisco Networking

18. Multi-area OSPF Layout
Switch
/24
/24
Area 1 E0
Router 1 E0
Router 2 S0
Area 2
/30 S1
/38
Router 3 S1 S0 E0 E0
/24
/24
Router 4
Area 0
6/1/2018
Valencia Community College
Cisco Networking

19. Valencia Community College
Router 1 configuration
6/1/2018
Valencia Community College
Cisco Networking

20. Valencia Community College
Router 2 configuration
6/1/2018
Valencia Community College
Cisco Networking

21. Valencia Community College
Router 3 Configuration
6/1/2018
Valencia Community College
Cisco Networking

22. Valencia Community College
Router 4 configuration
6/1/2018
Valencia Community College
Cisco Networking

23. Verifying and Managing OSPF
OSPF process
OSPF neighbors
Interface configuration
Link states
Timers
Debugging
6/1/2018
Valencia Community College
Cisco Networking

24. Valencia Community College
Issues
Redistributing ANYTHING into OSPF
Redistributing OSPF 1
6/1/2018
Valencia Community College
Cisco Networking

25. Valencia Community College
Issues
Lab closing on 14:00 on Friday.
No lab hours on weekends.
6/1/2018
Valencia Community College
Cisco Networking