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

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

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.

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.

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

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

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.

OSPF OPERATIONS OSPF Router Roles

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.

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.

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.

OSPF state transitions Neighbor States

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.

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!

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.

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”.

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 1.1.1.1 R1(config)#int gi0/0 R1(config-if)#ipv6 ospf 10 area 0.0.0.0 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

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.