Frame Relay Configuration Summary

For frame relay NBMA configuration, all we need is the encapsulation frame-relay command and the appropriate network protocol commands, such as ip address or decnet cost, on the physical interface connected to the frame relay network. In an NBMA environment, we may run into connectivity problems caused by split horizon (see Section 2.2.2.1, “Distance Vector Routing Protocols”).

The recommended frame relay configuration makes use of sub interfaces. All we have to do is issue the encapsulation frame-relay command on the physical interface, create a sub interface for each PVC, use the frame-relay interface-dlci command to assign a DLCI to each sub interface, and issue the appropriate network protocol command(s) on each sub interface. Using point-to-point sub interfaces removes the split horizon problems sometimes experienced in an NBMA environment.

Figure 19 shows the frame-relay-specific commands left in Dallas’s running configuration after our example work, Figure 20 shows those from FortWorth’s running configuration, and Figure 21 shows those from Austin’s running configuration.

1)  Dallas#show running-config [Some text has been omitted.]

2)  !

3)  interface Serial2

4)   encapsulation frame-relay

5)  !

6)  interface Serial2.1 point-to-point

7)   ip address 172.16.30.1 255.255.255.0

8)   frame-relay interface-dlci 100

9)  !

10) interface Serial2.2 point-to-point

11)  ip address 172.16.31.1 255.255.255.0

12)  frame-relay interface-dlci 102

13) !

14) router rip

15)  network 172.16.0.0

16) !

17) Dallas#

Figure 19: Dallas frame relay configuration commands.

1)  FortWorth#show running-config [Some text has been omitted.]

2)  !

3)  interface Serial2

4)   ip address 172.16.30.2 255.255.255.0

5)   encapsulation frame-relay

6)  !

7)  router rip

8)   network 172.16.0.0

9)  !

10) FortWorth#

Figure 20: FortWorth frame relay configuration commands.

1)  Austin#show running-config [Some text has been omitted.]

2)  !

3)  interface Serial2

4)   ip address 172.16.31.2 255.255.255.0

5)   encapsulation frame-relay

6)  !

7)  router rip

8)   network 172.16.0.0

9)   network 192.168.1.0

10) !

11) Austin#

Figure 21: Austin frame relay configuration commands.

Frame relay is currently very popular because it is usually less expensive than normal leased lines and because it is widely available. Frame relay is usually less expensive than leased lines because when we get a leased line, our service provider provides us with dedicated bandwidth, and when we get a frame relay PVC, our service provider provides us with just a share of their bandwidth (no dedicated). Our traffic has a greater chance of being dropped traversing a frame relay network than a leased line—yet another reason for the lower cost. Most companies are willing to accept these shortcomings because of the monetary savings, and most applications are not greatly affected as long as the frame relay configuration is properly implemented on both the user side and the service provider side.