Configuring OSPF for Multiple Areas and Frame Relay Nonbroadcast

For example, OSPF can be deployed in a hierarchical structure in which the network is divided into
OSPF zones called areas. In addition, OSPF operates differently on different types of interfaces.
This lab focuses on a multiple-area OSPF network, with Frame Relay (that is, nonbroadcast) interfaces.
Ethernet (that is, broadcast) interfaces are also addressed.

An OSPF troubleshooting scenario, integrated into this lab, explores the need for virtual links on
some OSPF networks. The objectives of this lab are as follows:
■ Reviewing OSPF network types
■ Configuring OSPF
■ Verifying OSPF neighbors and router IDs
■ Describing the need for virtual links
■ Configuring virtual links
■ Verifying end-to-end connectivity

Step 1: Configure and Verify Basic OSPF Connectivity—Initial Configurations

Initial Configuration for R1
hostname R1
!
interface Loopback0
ip address 1.1.1.1 255.255.255.255
!
interface Ethernet0
ip address 10.1.2.1 255.255.255.0
!
interface Serial0
ip address 10.1.1.1 255.255.255.0
encapsulation frame-relay IETF
frame-relay map ip 10.1.1.2 100 broadcast

Initial Configuration for R2
hostname R2
!
interface Loopback0
ip address 2.2.2.2 255.255.255.255
!
interface Ethernet0/0
ip address 172.16.1.2 255.255.255.0
half-duplex
!
interface Serial0/0
ip address 10.1.1.2 255.255.255.0
encapsulation frame-relay IETF
frame-relay map ip 10.1.1.1 200 broadcast

Initial Configuration for R3
hostname R3
!
interface Loopback0
ip address 3.3.3.3 255.255.255.255
!
interface FastEthernet0/0
ip address 172.16.1.3 255.255.255.0
duplex auto
speed auto
!
interface FastEthernet0/1
ip address 192.168.1.3 255.255.255.0
duplex auto
speed auto

Initial Configuration for R4
hostname R4
!
ip routing
!
interface Loopback0
ip address 4.4.4.4 255.255.255.255
!
interface GigabitEthernet0/1
no switchport
ip address 192.168.1.4 255.255.255.0

Configuration for FRSW
hostname FRSW
!
frame-relay switching
!
interface Serial0
encapsulation frame-relay IETF
clock rate 2000000
frame-relay lmi-type cisco
frame-relay intf-type dce
frame-relay route 100 interface Serial1 200
!
interface Serial1
no ip address
encapsulation frame-relay IETF
clock rate 2000000
frame-relay lmi-type cisco
frame-relay intf-type dce
frame-relay route 200 interface Serial0 100

Step 1: Configure and Verify Basic OSPF Connectivity— Ending Configurations

A portion of the topology used in this lab contains a Frame Relay network, which defaults to a nonbroadcast OSPF network type. Therefore, commands are added to establish an OSPF adjacency
across the Frame Relay network and to influence which of the routers connected to the Frame
Relay network is elected as the DR.

A DR reduces the number of required OSPF adjacencies by becoming adjacent with all the other
routers on the network segment. Some networks also have a Backup Designated Router (BDR),
which takes over DR duties if the DR fails.

Basic OSPF Configuration for Router R1
router ospf 1
network 1.1.1.1 0.0.0.0 area 0
network 10.1.1.0 0.0.0.255 area 0
network 10.1.2.0 0.0.0.255 area 0
neighbor 10.1.1.2

Basic OSPF Configuration for Router R2
interface Serial0/0
ip ospf priority 0
router ospf 1
network 2.2.2.2 0.0.0.0 area 0
network 10.1.1.0 0.0.0.255 area 0
network 172.16.1.0 0.0.0.255 area 1

Basic OSPF Configuration for Router R3
router ospf 1
network 3.3.3.3 0.0.0.0 area 1
network 172.16.1.0 0.0.0.255 area 1
network 192.168.1.0 0.0.0.255 area 2

Basic OSPF Configuration for Router R4
router ospf 1
network 4.4.4.4 0.0.0.0 area 2
network 192.168.1.0 0.0.0.255 area 2

Step 2: Configure OSPF Virtual Links

After the initial OSPF configuration, this lab shows that router R4 has learned no routes via OSPF.
The underlying issue is that in this lab’s topology, area 2 is not adjacent to area 0, and OSPF has a
requirement that all areas must be adjacent to area 0 (that is, the backbone area) in a multiple-area
OSPF network.

An OSPF virtual link can fix this issue by virtually linking an area to area 0. This virtual link
crosses another area, which you can think of as a transit area. To configure a virtual link across
this transit area, two routers must be configured for the virtual link.
One of the two routers is an area border router (ABR) that connects the transit area to area 0. The
other router that must be configured for the virtual link is an ABR that connects to both the transit
area and the area not adjacent to area 0.

Configuring a Virtual Link on R2
router ospf 1
area 1 virtual-link 3.3.3.3

Configuring a Virtual Link on R3
router ospf 1
area 1 virtual-link 2.2.2.2

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