111 © 2003, Cisco Systems, Inc. All rights reserved. CCNA 3: Switching Basics and Intermediate Routing v3.0

© 2003, Cisco Systems, Inc. All rights reserved. CCNA 3: Switching Basics and Intermediate Routing v3.0 2 Single Area OSPF Configuration CCNA 3 v3.0: Module 2

333 © 2003, Cisco Systems, Inc. All rights reserved. CCNA 3: Switching Basics and Intermediate Routing v3.0 OSPF Configuration Example The topology below will be used to demonstrate a step-by-step configuration of Single Area OSPF.

444 © 2003, Cisco Systems, Inc. All rights reserved. CCNA 3: Switching Basics and Intermediate Routing v3.0 Beginning Configurations The next three slides display the basic beginning configurations for RTA, RTB, and RTC. We will configure the ISP router later.

555 © 2003, Cisco Systems, Inc. All rights reserved. CCNA 3: Switching Basics and Intermediate Routing v3.0 RTA’s Beginning Configuration

666 © 2003, Cisco Systems, Inc. All rights reserved. CCNA 3: Switching Basics and Intermediate Routing v3.0 RTB’s Beginning Configuration

777 © 2003, Cisco Systems, Inc. All rights reserved. CCNA 3: Switching Basics and Intermediate Routing v3.0 RTC’s Beginning Configuration

888 © 2003, Cisco Systems, Inc. All rights reserved. CCNA 3: Switching Basics and Intermediate Routing v3.0 Below is the command to enable OSPF.  The process_id is used to identify the OSPF process.  The process id field is 16 bits; can be a number from 1 to 65,535.  You can have multiple instances of OSPF running on the same router, but this is not commonly done.  Unlike the AS argument in other routing protocols, the process id does not have to match other routers in the area. Basic OSPF Configuration Router(config)#router ospf process_id

999 © 2003, Cisco Systems, Inc. All rights reserved. CCNA 3: Switching Basics and Intermediate Routing v3.0 Basic OSPF Configuration Below is the command to advertise IP networks.  Just like RIP and IGRP, you enter the network command and address for each network you want OSPF to advertise.  The wildcard-mask argument is simply the mirror of the network’s subnet mask and is used to associate the network with its area.  The area command must be entered.  The area_id is a 32 bit number Router(config-router)#network address wildcard- mask area area-id

10 © 2003, Cisco Systems, Inc. All rights reserved. CCNA 3: Switching Basics and Intermediate Routing v3.0 Configure Basic OSPF Configure the OSPF routing process and directly connected networks.

11 © 2003, Cisco Systems, Inc. All rights reserved. CCNA 3: Switching Basics and Intermediate Routing v3.0 Verify Basic OSPF Configuration Use the show ip ospf neighbor command to verify each router has established adjacencies with its two neighbors. Use the show ip route command to verify all routers see all networks.

12 © 2003, Cisco Systems, Inc. All rights reserved. CCNA 3: Switching Basics and Intermediate Routing v3.0 Router Priority Use the ip ospf priority command on the interface participating in an OSPF area to configure which router will become the DR and BDR.  Router priority is 1 by default; 0 means “never DR.”  The number argument is 8 bits; value from 0 to 255  If the highest priority is shared by more than one router, then router ID determines DR/BDR. Router(config-if)#ip ospf priority number

13 © 2003, Cisco Systems, Inc. All rights reserved. CCNA 3: Switching Basics and Intermediate Routing v3.0 Loopback Interface To add stability to router IDs, use a configured loopback.  The highest loopback address will become the router’s ID instead of the highest configured IP address on an interface.  When configuring loopbacks, use a /32 mask to avoid potential routing problems.  Note: no shutdown command is not needed. Router(config)#interface loopback number Router(config-if)#ip address ip_add subnet_mask

14 © 2003, Cisco Systems, Inc. All rights reserved. CCNA 3: Switching Basics and Intermediate Routing v3.0 Configure Loopback Interfaces We configure one loopback interface on each router and then reload the routers to change the Router IDs.

15 © 2003, Cisco Systems, Inc. All rights reserved. CCNA 3: Switching Basics and Intermediate Routing v3.0 Verify New Router IDs Use the show ip ospf interface command to verify that the Router IDs are now the ip addresses of the loopback interfaces.

16 © 2003, Cisco Systems, Inc. All rights reserved. CCNA 3: Switching Basics and Intermediate Routing v3.0 Cost Calculation OSPF uses Cost as its only metric. OSPF calculates the cost of a link based upon the following formula:  10 8 /bps = Cost (Note: bps for 1K = 1000, not 1024)

17 © 2003, Cisco Systems, Inc. All rights reserved. CCNA 3: Switching Basics and Intermediate Routing v3.0 Modifying Cost Router’s must agree on the cost of a shared link. Otherwise, the link will be considered down.  In a multivendor environment, use the ip ospf cost command to make sure routers agree.  Use the bandwidth command to change the default to the actual, contracted bandwidth. Router(config-if)#ip ospf cost number Router(config-if)#bandwidth kps

18 © 2003, Cisco Systems, Inc. All rights reserved. CCNA 3: Switching Basics and Intermediate Routing v3.0 Sub-optimal Routes RTB and RTC are using the slower link between them to route packets.

19 © 2003, Cisco Systems, Inc. All rights reserved. CCNA 3: Switching Basics and Intermediate Routing v3.0 Configure Bandwidth Configure the correct bandwidth on RTB and RTC.

20 © 2003, Cisco Systems, Inc. All rights reserved. CCNA 3: Switching Basics and Intermediate Routing v3.0 Hello and Dead Intervals All routers in an OSPF area must agree on the same hello and dead intervals.  This is necessary to insure that each router knows when to consider any link to be down. Router(config-if)#ip ospf hello-interval seconds Router(config-if)#ip ospf dead-interval seconds

21 © 2003, Cisco Systems, Inc. All rights reserved. CCNA 3: Switching Basics and Intermediate Routing v3.0 Configure Hello and Dead Intervals Configure RTB and RTC to exchange hellos at a longer interval.

22 © 2003, Cisco Systems, Inc. All rights reserved. CCNA 3: Switching Basics and Intermediate Routing v3.0 Verify Hello and Dead Intervals Use the show ip ospf interface command to verify.

23 © 2003, Cisco Systems, Inc. All rights reserved. CCNA 3: Switching Basics and Intermediate Routing v3.0 OSPF Authentication is often used to insure only “desired” OSPF routers join the area.  By default, authentication is “null” meaning that routing updates are not authenticated.  Two methods for authenticating OSPF updates:  Simple password authentication  Message Digest authentication (MD-5) OSPF Authentication

24 © 2003, Cisco Systems, Inc. All rights reserved. CCNA 3: Switching Basics and Intermediate Routing v3.0 Simple Password Authentication The commands for simple password authentication are shown below:  All routers within the area must be configured with the same commands and password.  Passwords are sent across the link in clear text. Router(config-if)#ip ospf authentication-key key Router(config-router)#area area-id authentication

25 © 2003, Cisco Systems, Inc. All rights reserved. CCNA 3: Switching Basics and Intermediate Routing v3.0 Configure Simple Authentication Configure RTB and RTC with simple authentication.

26 © 2003, Cisco Systems, Inc. All rights reserved. CCNA 3: Switching Basics and Intermediate Routing v3.0 Verify Simple Authentication To verify simple authentication, use the show ip ospf command.

27 © 2003, Cisco Systems, Inc. All rights reserved. CCNA 3: Switching Basics and Intermediate Routing v3.0 Message Digest Authentication Two reasons to use MD-5 authentication:  Passwords are not sent  Admin. can change the password one router at a time without interrupting the routing process Router(config-if)#ip ospf message-digest-key key-id md5 encryption-type key Router(config-router)#area area-id authentication message-digest

28 © 2003, Cisco Systems, Inc. All rights reserved. CCNA 3: Switching Basics and Intermediate Routing v3.0 Configure MD5 Authentication Configure MD5 authentication on all OSPF interfaces and OSPF routing processes.

29 © 2003, Cisco Systems, Inc. All rights reserved. CCNA 3: Switching Basics and Intermediate Routing v3.0 Verify MD5 Authentication To verify MD5 authentication, use the show ip ospf command.

30 © 2003, Cisco Systems, Inc. All rights reserved. CCNA 3: Switching Basics and Intermediate Routing v3.0 Adding a Route to ISP Now we will add a link to the ISP router.

31 © 2003, Cisco Systems, Inc. All rights reserved. CCNA 3: Switching Basics and Intermediate Routing v3.0 Default Routes in OSPF Internal routers within an OSPF area need to know where to send packets addressed to destinations outside the area.  On the gateway router (RTA in our example):  Configure a static default route  Advertise the default route. Router(config)#ip route next-hop-ip Router(config-router)#default-information originate

32 © 2003, Cisco Systems, Inc. All rights reserved. CCNA 3: Switching Basics and Intermediate Routing v3.0 Configure Default Route RTA is connected to ISP and is the OSPF ASBR. Configure RTA’s E1 and a default route to ISP.  RTA can ping ISP’s loopback, but RTB and RTC can’t. Redistribute the default route to RTB and RTC.

33 © 2003, Cisco Systems, Inc. All rights reserved. CCNA 3: Switching Basics and Intermediate Routing v3.0 Verify Default Route RTB and RTC can now reach the Internet. RTB and RTC routing tables now show an external OSPF type 2 link. RTA’s routing table shows a candidate default static route.

34 © 2003, Cisco Systems, Inc. All rights reserved. CCNA 3: Switching Basics and Intermediate Routing v3.0 RTA’s Ending Configuration

35 © 2003, Cisco Systems, Inc. All rights reserved. CCNA 3: Switching Basics and Intermediate Routing v3.0 RTB’s Ending Configuration

36 © 2003, Cisco Systems, Inc. All rights reserved. CCNA 3: Switching Basics and Intermediate Routing v3.0 RTC’s Ending Configuration

37 © 2003, Cisco Systems, Inc. All rights reserved. CCNA 3: Switching Basics and Intermediate Routing v3.037