Some days ago, during my preparation for CCIE RS I had to configure Frame-Relay Hub and Spoke environment. Since I already did it, I said that is good to have it here also, maybe somebody will find it useful. Even if it sounds quite complicate as title, FR hub and spoke. This post assume that you are somehow familiar with Frame-Relay concept and you know basic stuff. If you need to refresh your knowledge there is good topic about Frame-Relay on Ciscopress page.
So, what is this FR hub and spoke anyway? A basic example is with 3 device (can be more) in which on of them connect the other ones in a central point. This is the opposite to (full or circular) mesh in which every router is connected with at least another 2 devices. For things to be more clear please have a look to this topology file.
As you can see in the topology provided, R1 is connecting the other 2 routers in a central point. R1 device is the Hub and R2, R3 are the Spokes. Like explained in the topology, the green lines represent PVC circuit and red ones the physical connection. The communication between R2 and R3 will be done only through R1 since there is no PVC that connect this 2 devices. You can be tempted to say that the communication is direct, because red lines have a common point in the FR switch, but the things are not like this. This is not Ethernet, so for L3 to work you need a map from L2 to L3. Since there is no PVC define in FR switch for R2 to R3 communication, everything is passing through R1.
To configure Frame-Relay Hub and Spoke is not very difficult. The most hard part is regarding FR switch, but luckily you don’t have to deal with it, as this is usually a provider equipment, and they will do the L2 to L3 frame-relay routing, providing you with the need DLCI information. From this point you only have to be careful to details (IP, DLCI, interface) when configuring frame-relay map on your devices.
In a future post I will extend this topic and show how you can configure OSPF in a Frame-Relay Hub and Spoke environment. For now please check this topic presented in the tutorial below:
If Flash movie is not available for you, then please check this text file which contains the configuration.