Frame Relay Configuration

There are two ways of configuring frame relay on a Cisco router. The first configuration method uses the classic, frame relay nonbroadcast multiaccess (NBMA) model. In this configuration, the frame relay network is treated as a multiaccess network like a LAN; however, unlike a LAN, a frame relay network has no broadcast capability. There is no frame relay broadcast address. All of the routers connected to the NBMA network share a network address such as an IP subnet address or an AppleTalk cable range. The second configuration method involves treating each of the PVCs as a separate logical point-to-point network, which is done by creating a sub interface for each PVC. The sub interface method requires more network addresses because each PVC has its own network address.

Of the two methods, the sub interface method is usually the recommended one. Both configuration methods are briefly described in the following sections.

We are going to move our IP traffic from the point-to-point serial links to a frame relay network. To do this, we are going to do something that is not normally recommended in a production network. We are going to remove the IP addresses from the point-to-point serial links, and we are going to stop the current IP routing protocol, OSPF, which was configured in Chapter 7. Figure 13-2 shows the IP configuration changes on Dallas, FortWorth, and Austin.

1)  Dallas#configure terminal

2)  Enter configuration commands, one per line. End with CNTL/Z.

3)  Dallas(config)#no router ospf 100

4)  Dallas(config)#interface serial0

5)  Dallas(config-if)#no ip address

6)  Dallas(config-if)#interface serial1

7)  Dallas(config-if)#no ip address

8)  Dallas(config-if)#<Ctrl-Z>

9)  Dallas#

10) —————

11) FortWorth#configure terminal

12) Enter configuration commands, one per line. End with CNTL/Z.

13) FortWorth(config)#no router ospf 200

14) FortWorth(config)#interface serial0

15) FortWorth(config-if)#no ip address

16) FortWorth(config-if)#interface serial1

17) FortWorth(config-if)#no ip address

18) FortWorth(config-if)#<Ctrl-Z>

19) FortWorth#

20) —————

21) Austin#configure terminal

22) Enter configuration commands, one per line. End with CNTL/Z.

23) Austin(config)#no router ospf 300

24) Austin(config)#interface serial0

25) Austin(config-if)#no ip address

26) Austin(config-if)#interface serial1

27) Austin(config-if)#no ip address

28) Austin(config-if)#<Ctrl-Z>

29) Austin#

Figure 2: Removal of IP from point-to-point serial links.

After issuing the commands in Figure 2, IP is no longer being routed across our WANs. We will restore IP connectivity by configuring frame relay on the routers.