Frame Relay Subinterface Command List

Frame Relay Subinterface Command List

Frame Relay Subinterface Command List

Using subinterfaces also lets you send routing updates out the same physical interface on which they were received. Using subinterfaces in this manner overcomes the split horizon problem that can occur when sending updates out the same interface. To configure Frame Relay on a subinterface, complete the following tasks:

• Enable Frame Relay on the interface and set the encapsulation method.
• Create the subinterface, specifying either point-to-point or multipoint.
• For a point-to-point connection or a multipoint connection using inverse ARP, assign the DLCI number to the subinterface.
• For a multipoint connection using static assignments, map DLCIs to protocol addresses.

In addition, you will need to assign a Network layer address to the subinterface. Do not assign an IP address to the main interface.

Use . . .	To . . .
Router(config-if)#int sX.X	Create the subinterface
Router(config-subif)#frame-relay interface-dlci	Assign the DLCI to the interface
Router(config-subif)#frame-relay map	Map protocol addresses to DLCIs

Examples
The following commands create a point-to-point subinterface on the first serial interface and assign it to DLCI 44. The subinterface is configured to use inverse ARP.

Router(config)#int s0

Router(config-if)#encap frame

Router(config-if)#int s0.55 point

Router(config-subif)#frame interface-dlci 44

The following commands create a multipoint subinterface on the second serial interface, and configure it with a static IP mapping of device 199.12.16.155 to DLCI 111.

Router(config)#int s1

Router(config-if)#encap frame

Router(config-if)#int s1.103 mult

Router(config-subif)#frame map ip 199.12.16.155 111

Frame Relay Map Command List

Frame Relay Map Command List

Frame Relay Map Command ListUse the frame-relay map command to create the static mapping, associating IP addresses with DLCI numbers.

• Add the broadcast parameter to the command to configure the router to forward broadcast traffic over the link.
• You can also specify the Frame Relay encapsulation to use for the virtual circuit by adding the cisco or the ietf keywords. If not used, the circuit uses the encapsulation method specified for the interface. If used, you can use one type of encapsulation for one DLCI, and another type for another DLCI.

The following commands enable Frame Relay on serial interface 0 using Cisco as the encapsulation method, disable inverse ARP, and map IP address 10.1.1.55 to DLCI 25.

Router(config)#int s0
Router(config-if)#encap frame-relay
Router(config-if)#no frame inverse
Router(config-if)#frame-relay map ip 10.1.1.55 25

Frame Relay Facts

Frame Relay Facts

Frame Relay Facts

Frame relay is a standard for packet switching WAN communications over high-quality, digital lines. Frame-relay networks:

• Provide error detection but not error recovery. It is up to end devices to request a retransmission of lost packets.
• Can provide data transfer up to 1.54 Mbps.
• Have a variable packet size (called a frame).
• Can be used as a backbone connection to LANs.
• Can be implemented over a variety of connection lines (56K, T-1, T-3).
• Operate at the Physical and Data Link layers of the OSI model.

When you sign up for Frame Relay service, you are assigned a level of service called a Committed Information Rate (CIR). The CIR is the maximum guaranteed data transmission rate you will receive on the Frame Relay network. When network traffic is low, you will likely be able to send data faster than the CIR. As network traffic increases, priority is given to data coming from customers with a higher CIR, and the effective rate may drop. In any case, you are guaranteed to have at least the amount of bandwidth specified by the CIR.

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.

Frame Relay Addressing Facts

Frame Relay Addressing Facts

Frame Relay Addressing Facts

Most Frame Relay installations involve connecting to a Frame Relay network through a T-1 line. The router connects to a CSU/DSU, which is connected to the Frame Relay network. The Frame Relay network is made up of multiple switches for moving packets. You should be aware of the following Frame Relay concepts:

Concept	Description
Data-Link Connection Identifier (DLCI)	Like an Ethernet MAC address, a DLCI identifies each virtual circuit. The DLCI ranges between 16 and 1007. The DLCI represents the connection between two frame relay devices. The Frame Relay service provider assigns the DLCI when the virtual circuit is set up. Each DLCI is unique for the local network, but not for the entire WAN. In other words, the same DLCI number can be used multiple times in the entire network to identify different devices.
Local Management Interface (LMI)	Local Management Interface (LMI) is a set of management protocol extensions that automates many Frame Relay management tasks. LMI is responsible for managing the connection and reporting connection status. LMI can: Maintain the link between the router and the switch. Gather status information about other routers and connections on the network. Enable dynamic DLCI assignment through multicasting support. Make DLCIs globally significant for the entire network. Although DLCI numbers are only locally significant, through LMI these numbers can be globally significant (i.e. the same number is used throughout the entire network to identify a specific link). Cisco routers support three LMI types: Cisco, ANSI, and Q933a.