Frame Relay is a protocol standard for WAN internetworking which provides a fast and efficient method of transmitting packets through the network. Frame Relay offers an attractive alternative to both dedicated lines and X.25 networks for WAN links. The success of the Frame Relay protocol is based on the following two factors:
- Virtual circuits consume bandwidth only when they transport data. Consequently, many virtual circuits can exist across a given transmission line, which is an improvement compared to dedicated leased lines. In addition, each device can use more than the allowed bandwidth as necessary, and thus operate at higher speeds.
- The increased error-handling sophistication at end stations and the improved reliability of communication lines allows the Frame Relay protocol to discard bad frames and thus eliminate time-consuming error-handling processing.
Cisco Packet Tracer 7.2.1 includes a "Cloud-PT" device for WAN emulation. This device can be configured as a Frame Relay switch. Router are connected to the Frame Relay switch using serial connections. Virtual circuits, LMI types, and DLCI are configured using the Serial and Frame Relay tabs of the "Cloud-PT" device.
Network topology used in this tutorial
A hub and sopke sample network topology is created in Cisco Packet Tracer 7.2.2 :
- R0 router is the spoke router
- R1 and R2 routers are frame-relay spokes
- All frame relay routers are interconnected through a Cisco Packet Tracer Cloud device which emulates frame relay circuits.
Frame Relay configuration - WAN cloud
Configure the LMI type and DLCI of virtual circuits on each serial interface of the cloud used for Frame Relay operation.
Create the virtual circuits one the "Frame Relay" tab. DLCI's need to be configured on the "Serial" tabs before creating virtual circuits.
Frame Relay configuration - ISR router configuration
Frame relay hub router configuration (R0)
The hub router is configured with two sub-interfaces to create a virtual circuit with each spoke. Each frame relay sub-interface is mapped with the DLCI number of the corresponding circuit configured in the Packet Tracer WAN emulation Cloud. The DLCI number defines a single virtual connection through the WAN and are the Frame Relay equivalent to a hardware address.
The encapsulation frame-relay command is mandatory on the main serial interface before configuring frame-relay sub interfaces.
The clock rate defines the speed on the serial interface
interface Serial0/0/0 no ip address encapsulation frame-relay ! interface Serial0/0/0.101 point-to-point ip address 192.168.101.1 255.255.255.252 frame-relay interface-dlci 101 clock rate 2000000 ! interface Serial0/0/0.102 point-to-point ip address 192.168.102.1 255.255.255.252 frame-relay interface-dlci 102 clock rate 2000000
Frame relay spoke routers configuration (R1 and R2)
The spoke routers have only one virtual circuit configured to reach the hub router. The DLCI configured on both spoke routers is the same as the DLCI is locally significant between the WAN Cloud and each customer.
Router R1 configuration
interface Serial0/0/0 ip address 192.168.101.2 255.255.255.252 encapsulation frame-relay frame-relay interface-dlci 100 !
Router R2 configuration
interface Serial0/0/0 ip address 192.168.102.2 255.255.255.252 encapsulation frame-relay frame-relay interface-dlci 100 !