This document provides an overview of OSPF including terminology, router types, link state advertisements (LSAs), network types, and the steps of OSPF operation. It discusses establishing adjacencies, electing designated routers, discovering routes, selecting routes, and maintaining routing information. It also covers configuring and verifying OSPF within a single area, over non-broadcast multi-access (NBMA) networks, and across multiple areas. Special area types like stub, totally stubby, and not-so-stubby areas are explained as well as using virtual links.

1. OSPF

2. Objectives
• OSPF Overview (terminology, states, network types,
hello protocol)
• Single-area OSPF Operation
• Single-area OSPF Configuration and Verification
• Configuring OSPF Over NBMA
• Multiarea OSPF Operation
• Multiarea OSPF Configuration and Verification
• (Standard, Backbone), Stub, Totally Stubby-CISCO,
and Not-So-Stubby Areas
• Virtual Links

3. OSPF router types
• routers exchange LSAs via muticast;
• various types of LSA:
– Type 1 LSA router,
– Type 2 LSA network,
– Type 3 LSA network summary,
– Type 4 LSA ASBR next hope reachability,
– Type 5 LSA external LSA and
– Type7 LSA external NSSA route

4. Some OSPF terminologies
• Area, 32 bit number (various types - Hierarchy based, Area 0=Backbone area)
• routers; router ID, lo0 (various types: Internal router, ABR, ASBR, Backbone Router … combination of the above) COMING SOON
• Link
• Cost
• Link state (ex. a router announce it is connected to router A on network 11.0.0.0/8, cost 5)
• Adjacencies
• DR, BDR DROthers (Broadcast or NBMA network)
• OSPF packets (Hello, DBD, LSR, LSU and LSack) NEXT SLIDE
• LSA: LSUs transport LSA (routers exchange LSAs via muticast; various types: LSA 1 router, 2 network, 3 network summary, 4
ASBR next hope reachability, 5 external LSA and 7 external NSSA route)
• Topological Database (identical database)
• SPF
• routing table

5. OSPF packet types

6. Steps to OSPF Operation
NEXT slide

7. Steps to OSPF Operation with States
1. Establishing router adjacencies (Routers are adjacent)
–Down State – No Hello received
–Init State – Hello received, but not with this router’s Router ID
•“Hi, my name is Carlos.” “Hi, my name is Maria.”
–Two-way State – Hello received, and with this router’s Router ID
•“Hi, Maria, my name is Carlos.” “Hi, Carlos, my name is Maria.”
2. Electing DR and BDR – Multi-access (broadcast) segments
only
–ExStart State with DR and BDR
–Two-way State with all other routers
3. Discovering Routes (coming soon)
–ExStart State
–Exchange State
–Loading State
–Full State (Routers are “fully adjacent”)
4. Calculating the Routing Table
5. Maintaining the LSDB and Routing
Table

8. OSPF network types

9. The OSPF Hello protocol

10. OSPF Operation
• Steps of OSPF operation
• Step 1: Establish router adjacencies
• Step 2: Elect a DR and a BDR
• Step 3: Discover routes
• Step 4: Select appropriate routes
• Step 5: Maintain routing information

11. Step 1: Establish router
adjacencies

12. Step 2: Elect a DR and a BDR

13. Step 3: Discover routes
–Down State – No Hello received
–Init State – Hello received, but not with this router’s Router ID
•“Hi, my name is Carlos.” “Hi, my name is Maria.”
–Two-way State – Hello received, and with this router’s Router ID
•“Hi, Maria, my name is Carlos.” “Hi, Carlos, my name is Maria.”

14. Step 4: Select appropriate routes

15. Step 5: Maintain routing
information

16. OSPF Configuration and
Verification
• Configuring OSPF on routers within a
single area
• Optional configuration commands
• Optional configuration commands
(continued)
• Show commands
• Clear and debug commands

17. Configuring OSPF on routers
within a single area
Rtr(config)# router ospf process-id
Rtr(config-router)#network address wildcard-mask area area-id

18. Optional configuration commands

19. Optional configuration commands
(continued)
CISCO Routers use the formula = 108/bandwidth
Rtr(config-if)# bandwidth 64 = Rtr(config-if)# ip ospf cost 1562
Rtr(config-if)# bandwidth kilobits
Rtr(config-if)# ip ospf authentication-key passwd
Rtr(config-router)# area “area” authentication
Rtr(config-if)# ip ospf message-digest-key key-id md5 password
Rtr(config-router)# area area authentication [message-digest]

20. Show commands

21. Clear and debug commands

22. Configuring OSPF Over NBMA
• NBMA overview
• Full-mesh Frame Relay
• Partial-mesh Frame Relay
– Point-to-Multipoint OSPF

23. NBMA overview

24. Full-mesh Frame Relay

25. Partial-mesh Frame Relay

26. Point-to-Multipoint OSPF

27. Multiarea OSPF Operation
• The routing table is too big, the memory is
running low
– Creating multiple OSPF areas
• OSPF router types
• OSPF LSA and area types
• Configuring OSPF operation across multiple
areas
• Flooding LSUs to multiple areas
• Updating the routing table

28. OSPF router types
• routers exchange LSAs via muticast;
• various types of LSA:
– Type 1 LSA router,
– Type 2 LSA network,
– Type 3 LSA network summary,
– Type 4 LSA ASBR next hope reachability,
– Type 5 LSA external LSA and
– Type7 LSA external NSSA route

29. OSPF LSA and area types

30. Flooding LSUs to multiple areas

31. Multiarea OSPF Configuration
and Verification
• Using and configuring OSPF multiarea
components
• Configuring OSPF route summarization
• Verifying multiarea OSPF operation

32. Using and configuring OSPF
multiarea components

33. Configuring OSPF route
summarization
Router(config-router)# area area-id range network-address subnet-mask
Router(config-router)# summary-address network-address subnet-mask

34. Verifying multiarea OSPF
operation

35. Stub, Totally Stubby, and Not-So-
Stubby Areas
• Using stub and totally stubby areas
• Stub and totally stubby area criteria
• Configuring stub and totally stubby areas
• OSPF stub area configuration example
• OSPF totally stubby area configuration
example
• NSSA overview
• How NSSA operates
• Configuring NSSA

36. Using stub and totally stubby
areas

37. Stub and totally stubby area
criteria

38. OSPF stub area configuration
example

39. OSPF totally stubby area
configuration example

40. NSSA overview

41. Operation and Configuration of
NSSA

42. Virtual Links
• Meeting the backbone area
requirements
• Configuring virtual links
• Virtual link configuration example

43. Meeting the backbone area
requirements

44. Virtual link configuration example