Frame Relay Configuration Facts

Frame Relay Configuration Facts

Frame Relay Configuration Facts

When configuring a router for Frame Relay, the DLCI number acts like a Data Link or physical device address. Because Frame Relay supports multiple upper-layer protocols (such as IP, IPX, and DECnet), you will need to associate logical, Network layer destination addresses with the DLCI number used to reach that address. For multipoint connections, you have the following configuration options.

Configuration Method	Description
Inverse ARP	The router uses the inverse ARP protocol to dynamically discover destination addresses associated with a specific DLCI. To use inverse ARP, simply enable Frame Relay encapsulation on the interface. Using inverse ARP is the default.
Manual mappings	The administrator identifies the address of each destination device, and associates each address with a DLCI. Although more work, results are less prone to errors than when using inverse ARP.
Subinterfaces	A subinterface is a virtual interface that you configure on a Cisco router's physical interface. Instead of adding physical interfaces, using subinterfaces lets you subdivide a single physical interface into several separate virtual channels. Subinterfaces make it possible to support multiple connections and/or networks through a single physical port. When you connect a router to the Frame Relay network, the router interface has a direct line to the Frame Relay switch at the service provider. Although there is only one physical path between the router and the switch, Frame Relay supports multiple virtual circuits. When configuring a Frame Relay connection or circuit, you have the following options: Point-to-Point. A point-to-point link simulates a direct connection with a destination device. With a point-to-point connection, the circuit is configured to talk to only one other device. Multipoint. A multipoint link configures each circuit to communicate with more than one destination device. The same circuit is used for multiple conversations. To configure a subinterface for Frame Relay, you set the encapsulation type, then assign a DLCI number to the subinterface or use manual mappings to identify IP address and DCLI pairs.

To configure Frame Relay on an interface, complete the following tasks:

• Enable Frame Relay on the interface by setting the encapsulation type.
• Assign a Network layer address to the interface (such as an IP address).
• Configure dynamic (inverse ARP) or static (mapped) addresses.
• For a point-to-point subinterface, or a multipoint subinterface with dynamic addressing, assign a DLCI to the subinterface.
• Configure the LMI settings (optional). By default, Cisco routers autosense the LMI type and configure themselves accordingly. You only need to set the LMI type if autosensing does not work or if you want to manually assign it.

Note: You must set the encapsulation method on the interface before you can issue any other Frame Relay commands.