© 2003, Cisco Systems, Inc. All rights reserved.

2 Building Scalable Cisco Internetworks (BSCI) Version 2.0 Instructor Name

Configuring the OSPF Protocol © 2003, Cisco Systems, Inc. All rights reserved. 3

Configuring Basic Open Shortest Path First © 2003, Cisco Systems, Inc. All rights reserved. 4

BSCI 2.0—4-5 Objectives Upon completing this lesson, you will be able to: Configure and verify a basic single area Open Shortest Path First (OSPF) configuration Use OSPF configuration commands to properly enable the OSPF routing process

© 2003, Cisco Systems, Inc. All rights reserved. BSCI 2.0—4-6 router ospf process-id Router(config)# Turns on one or more OSPF routing processes in the IOS software. Configuring Basic OSPF: Single Area network address inverse-mask area [area-id] Router(config-router)# Router OSPF subordinate command that defines the interfaces (by network number) that OSPF will run on. Each network number must be defined to a specific area.

© 2003, Cisco Systems, Inc. All rights reserved. BSCI 2.0—4-7 Configuring OSPF on Internal Routers of a Single Area

© 2003, Cisco Systems, Inc. All rights reserved. BSCI 2.0—4-8 show ip protocols Router# Verifies the configured IP routing protocol processes, parameters and statistics Verifying OSPF Operation show ip route ospf Router# Displays all OSPF routes learned by the router show ip ospf interface Router# Displays the OSPF router ID, area ID and adjacency information

© 2003, Cisco Systems, Inc. All rights reserved. BSCI 2.0—4-9 show ip ospf Router# Displays the OSPF router ID, timers, and statistics Verifying OSPF Operation (Cont.) show ip ospf neighbor [detail] Router# Displays information about the OSPF neighbors, including Designated Router (DR) and Backup Designated Router (BDR) information on broadcast networks

© 2003, Cisco Systems, Inc. All rights reserved. BSCI 2.0—4-10 The show ip route ospf Command RouterA# show ip route ospf Codes:C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP, D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area, E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP, i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default Gateway of last resort is not set is subnetted, 2 subnets O [110/10] via , 00:00:50, Ethernet0

© 2003, Cisco Systems, Inc. All rights reserved. BSCI 2.0—4-11 The show ip ospf interface Command RouterA# show ip ospf interface e0 Ethernet0 is up, line protocol is up Internet Address /24, Area 0 Process ID 1, Router ID , Network Type BROADCAST, Cost: 10 Transmit Delay is 1 sec, State DROTHER, Priority 1 Designated Router (ID) , Interface address Backup Designated router (ID) , Interface address Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5 Hello due in 00:00:04 Neighbor Count is 1, Adjacent neighbor count is 1 Adjacent with neighbor (Designated Router) Suppress hello for 0 neighbor(s)

© 2003, Cisco Systems, Inc. All rights reserved. BSCI 2.0—4-12 The show ip ospf neighbor Command RouterB# show ip ospf neighbor Neighbor ID Pri State Dead Time Address Interface FULL/BDR 00:00: Ethernet FULL/- 00:00: Serial0

© 2003, Cisco Systems, Inc. All rights reserved. BSCI 2.0—4-13 OSPF Router ID The router is known to OSPF by the OSPF router ID number. LSDBs use the OSPF router ID to differentiate one router from the next. By default: the Router ID is the highest IP address on an active interface at the moment of OSPF process startup. A loopback interface can override OSPF router ID. It is the highest IP address of any active loopback interface. An OSPF router-id command can override OSPF router ID. The loopback or router-id command is recommended for stability.

© 2003, Cisco Systems, Inc. All rights reserved. BSCI 2.0—4-14 Loopback Interfaces interface loopback 0 ip address If the OSPF process is already running, the OSPF process must be cleared before the new router-id command will take effect. Router(config)# Router(config-if)#

© 2003, Cisco Systems, Inc. All rights reserved. BSCI 2.0—4-15 router-id ip-address This command is subordinate to the router-id ospf command. Any unique IP address can be used. If this command is used on an OSPF process that is already active, then the new router ID is used at the next reload or at a manual OSPF process restart using the clear ip ospf process command. OSPF router-id command router ospf 1 router-id Router(config-router)# Router(config)# Router(config-router)#

© 2003, Cisco Systems, Inc. All rights reserved. BSCI 2.0—4-16 OSPF Router ID Verification RouterA# show ip ospf Routing Process "ospf 1" with ID Supports only single TOS(TOS0) routes SPF schedule delay 5 secs, Hold time between two SPFs 10 secs Number of DCbitless external LSA 0 Number of DoNotAge external LSA 0 Number of areas in this router is 1. 1 normal 0 stub 0 nssa Area BACKBONE(0) (Active) Number of interfaces in this area is 2 Area has no authentication SPF algorithm executed 10 times Area ranges are Link State Update Interval is 00:30:00 and due in 0:07:16 Link State Age Interval is 00:20:00 and due in 00:07:15 Number of DCbitless LSA 0 Number of indication LSA 0 Number of DoNotAge LSA 0

© 2003, Cisco Systems, Inc. All rights reserved. BSCI 2.0—4-17 Summary This lesson presented these key points: Configuration of OSPF in a single area is a two-step process: –Turn on OSPF with the router ospf command. –Use the network statement to describe which interfaces will run OSPF. OSPF configuration requires each interface to be assigned to an area number. OSPF elects a router ID at startup time using the following techniques: –Highest IP address of all interfaces. –IP address of the loopback address. –A router-id command under the OSPF process.