1. Cisco networking, CNET-448
Chapter Introduction
Cisco networking, CNET-448
Chapter 6
Multi-Area OSPF
Prepared by: Sikandar Shah

2. Objectives IP Routing Technologies covered in this chapter are,
Chapter Objectives
Objectives
IP Routing Technologies covered in this chapter are,
IP Routing Technologies
neighbor adjacencies
OSPF states
Discuss Multi area
Configure OSPF v2
Configure OSPF v3
Router ID
LSA types
Troubleshooting
Troubleshoot and Resolve routing issues
routing is enabled
routing table is correct
correct path selection
Troubleshoot and Resolve OSPF problems
Hello and Dead timers
OSPF area
Interface MTU
Network types
Neighbor states
OSPF topology database

3. IP ROUTING
OSPF Scalability
OSPF is designed in a hierarchal passion, larger networks are divided into smaller network called areas.
Each router recalculates its database every time there’s a topology change.
Every time a link goes up or down, an LSA Type 1 packet is advertised, forcing all of the routers in the same area to recalculate their shortest path first (SPF) tree.
Every router will need to hold the entire link-state database representing the topology and a larger routing table.
OSPF allows us to take a large OSPF topology and break it down into multiple, more manageable areas.

4. Link State Advertisements(LSAs)
OSPF LSAs
Link State Advertisements(LSAs)
It describe a router and the networks that are connected to it.
Routers exchange LSAs and learn the complete topology of the network until all routers have the same topology database.
OSPF uses the Dijkstra algorithm to find the best path to each remote network and places best routes into the routing table.

5. Neighbors & Adjacency Requirements
OSPF OPERATIONS
Neighbors & Adjacency Requirements
Two steps required to change a neighboring OSPF router into an adjacent router:
Hello received, two way communication
Database synchronization, which consists of three packet types being exchanged between routers,
Database Description (DD) packets
Link-state Request (LSR) packets
Link-state Update (LSU) packets

6. Adjacency Conditions Same Area ID Same Subnet
OSPF OPERATIONS
Adjacency Conditions
Same Area ID
Same Subnet
Same Hello and dead intervals (Default 10, 40)
Authentication

7. OSPF Router Roles OSPF OPERATIONS
Backbone Routers: Any router that exists either partially or completely in OSPF area 0.
Area Border Routers(ABRs): An ABR is a router that belongs to more than one OSPF area. It maintains information from all directly connected areas in its topology table.
Internal Routers: An internal router is any router with all of its interfaces included as a member of the same area.
Autonomous system boundary router(ASBR): It is an OSPF router with at least one interface connected to an external network or different AS.

8. OSPF OPERATIONS
OSPF Router Roles

9. Link-state Advertisements
OSPF LSAs
Link-state Advertisements
Type 1 LSA: Referred to as a router Link advertisement (RLA). It is sent by every router to other routers in its area. It contains the router ID (RID), interface IP information and current state.
Type 2 LSA: Referred to as a Network Link Advertisement (NLA). It is generated by Designated router, it contains DR and BDR IP information.
Type 3 LSA: Referred to as a Summary Link Advertisement (SLA). It is generated by Area Border Routers (ABRs) toward the area external to the one where they were generated.

10. Link-state Advertisements
OSPF LSAs
Link-state Advertisements
Type 4 LSA : Type 4 LSAs are generated by area border routers. Type 4 are specifically used to inform the rest of the OSPF areas how to get to the ASBR.
Type 5 LSA: Referred to as AS external link advertisements, a Type 5 LSA is sent by autonomous system boundary routers to advertise routes that are external to the OSPF autonomous.

11. OSPF Hello Protocol Terms
OSPF TERMINOLOGY
OSPF Hello Protocol Terms
Router ID (RID): This is the highest active IP address on the router. The highest loopback IP addresses are used first.
Hello/Dead interval: The period between Hello packets is the Hello time, which is 10 seconds by default. The dead time is the length of time allotted before a neighbor is considered down.
Neighbors: The information includes a list of the router IDs for all the originating router’s.
Area ID: This represents the area that the originating router interface belongs to.
Router priority: The priority is an 8-bit value used to aid in the election of the DR and BDR on multi-access networks. It is from 0-255, 0 is the best.

12. OSPF state transitions
Neighbor States

13. OSPF state transitions
Neighbor States
DOWN: In the DOWN state, no Hello packets have been received on the interface.
ATTEMPT: It applies only to NBMA networks.
INIT: Hello packets have been received from another router with no Router ID’s but bidirectional communication hasn’t been established yet.
2WAY: Hello packets which include their own router IDs in the Neighbor field have been received.
EXSTART: The DR and BDR establish adjacencies with each router in the network. A master-slave relationship is created between each router and its adjacent DR and DBR.

14. OSPF state transitions
Neighbor States
EXCHANGE: Routing information is exchanged using Database Description (DBD or DD) packets and Link-State Request (LSR) and Link-State Update(LSU) packets.
LOADING: In the LOADING state, Link-State Request (LSR) packets are sent to neighbors to request any Link-State Advertisements (LSAs) that may have been missed or corrupted while the routers were in the EXCHANGE state.
FULL: In the FULL state, all LSA information is synchronized among neighbors and adjacency has been established. OSPF routing can begin only after the FULL state has been reached!

15. OSPF Verfication OSPF verification & troubleshooting
Command Provides the following
show ip ospf neighbor Verifies your OSPF-enabled interfaces
show ip ospf interface Displays OSPF-related information on an OSPF- enabled interface
show ip protocols Verifies the OSPF process ID and that OSPF is enabled on the router
show ip route Verifies the routing table, and displays any OSPF injected routes.
sh ip route ospf To display only OSPF routes
show ip ospf database Lists a summary of the LSAs in the database, with one line of output
per LSA, organized by type. It gives information about the number
of routers in the internetwork(AS).
Show ip ospf TO o display OSPF information for one or all OSPF processes
running on the router. Information contained therein includes the
router ID, area information, SPF statistics, and LSA timer information.

16. OSPF verification & troubleshooting
Troubleshooting OSPF
The first step is to check connectivity with ping and traceroute commands.
Verify adjacency using “show ip ospf neighbors”, verify hello, dead timers and area ID
verify that the interfaces are operational and enabled for OSPF.
verify the hello and dead timers next, and establish that the interfaces are in the same area
Use show ip route command to verify the routes to all networks.
Use show ip protocols to see all routing protocols running on your router.
Verify the networks statements under OSPF process.
Verify the link cost with the “show if ospf interface”.

17. OSPF IPV6
OSPFv3
In v3, RID, area ID and Link-state ID are still 32-bit.
To send updates and acknowledgements it uses FF02::5 for OSPF routers and FF02::6 for Designated routers.
OSPFv3 configuration
R1(config)#ipv6 router ospf 10
R1(config-rtr)# router-id
R1(config)#int gi0/0
R1(config-if)#ipv6 ospf 10 area
R2(config)#int gi0/0
R2(config-if)#ipv6 ospf 10 area 1
R1#show ipv6 route ospf
The OSPF routes are represented with O and OI.
O: Intra-area routes, routes from inside an area
OI: Inter-area routes, routes from a different area

18. Written Labs and Review Questions
Further Study
Written Labs and Review Questions
Read through the Exam Essentials section together in class
Open your books and go through all the written labs and the review questions.
Review the answers in class.