Frame Relay Switching over a Tunnel

In 1996 Cisco Systems to Join with StrataCom, a leading supplier of Asynchronous Transfer Mode (ATM) and Frame Relay high-speed wide area network (WAN) switching equipment that integrates and transports a wide variety of information, including voice, data and video.
Cisco MGX Multiservice Switches provide Frame Relay services at the Provider Edge.
In a lab situation, we can configured Cisco IOS on standard routers and access servers to provide frame relay services.

There are several ways to relay frames in IOS:

1. DCE-DCE (multiple DCE interfaces), basic switching using frame-route command
2. DCE-DCE (multiple DCE interfaces, on newer IOS such as 12.2T), using connect command
3. Hybrid, 1 DCE and 1 DTE
   
4. Back-to-Back, which requires lmi to be disabled with no keepalive
   
5. Tunnel Methods
   

To learn how to configure Cisco router as a Frame Relay switch, you can read my friend's blog, awa here.

Here I will give some configuration examples of Frame Relay switch using Tunnel methods.
Suppose you need 4 ports Frame Relay Switch for making a Full Mesh Frame Relay topology, but all you had is only 2 Cisco routers with 2 serials and 1 ethernet interfaces.
IOS permits us to send a switched frame relay packets over an IP tunnel. This permits the frame relay encapsulated serial interfaces to be located on different routers.
This diagram below may be looked complex, but its only just a Full Mesh Frame Relay topology.
















There are 2 fundamental tricks use to get this trick to work:

1. Using tunnel interface as the destination in the frame-route statements
2. Making the same PVC is referenced by the same DLCI on both side of the tunnels

Configuration of SW1:

interface serial 0
no ip address
encapsulation frame-relay
no fair-queue
clock rate 128000000
frame-relay intf-type dce
frame-route 102 interface Tunnel0 122
frame-route 103 interface Tunnel0 123
frame-route 104 interface Serial3 401

interface tunnel 0
ip unnumbered ethernet 0
tunnel source ethernet 0
tunnel destination 172.16.10.5

Configuration of SW2:

interface serial 1/0
no ip address
encapsulation frame-relay
clock rate 128000000
frame-relay intf-type dce
frame-route 201 interface Tunnel0 122
frame-route 203 interface Serial1/1 302
frame-route 204 interface Tunnel0 422

interface tunnel 0
ip unnumbered FastEthernet 0/0
tunnel source FastEthernet 0/0
tunnel destination 172.16.10.7