configured as a point-to-point connection. This allows each subinterface to act similarly to a leased line. Using a Frame Relay point-to-point subinterface, each pair of the point-to-point routers is on its own subnet. Frame Relay subinterfaces can be configured in either point-to-point or multipoint mode:

Point-to-point – A single point-to-point subinterface is used to establish one PVC connection to another physical interface or subinterface on a remote router. In this case, each pair of the point-to-point routers is on its own subnet and each point-to-point subinterface would have a single DLCI. In a point-to-point environment, each subinterface is acting like a point-to-point interface. Therefore, routing update traffic is not subject to the split-horizon rule.
Multipoint – A single multipoint subinterface is used to establish multiple PVC connections to multiple physical interfaces or subinterfaces on remote routers. All the participating interfaces would be in the same subnet. The subinterface acts like an NBMA Frame Relay interface so routing update traffic is subject to the split-horizon rule.

The encapsulation frame-relay command is assigned to the physical interface. All other configuration items, such as the network layer address and DLCIs, are assigned to the subinterface. Multipoint configurations can be used to conserve addresses that can be especially helpful if Variable Length Subnet Masking (VLSM) is not being used. However, multipoint configurations may not work properly given the broadcast traffic and split-horizon considerations. The point-to-point subinterface option was created to avoid these issues. Web Links Configuring Frame Relay Subinterfaces http://www.cisco.com/en/US/tech/
tk713/tk237/technologies_configuration_
example09186a008009421e.shtml

Content 5.2 Configuring Frame Relay 5.2.5 Configuring Frame Relay subinterfaces The Frame Relay service provider will assign the DLCI numbers. These numbers range from 16 to 992, and usually have only local significance. DLCIs can have global significance in certain circumstances. This number range will vary depending on the LMI used. In the figure, router A has two point-to-point subinterfaces. The s0/0.110 subinterface connects to router B and the s0/0.120 subinterface connects to router C. Each subinterface is on a different subnet. To configure subinterfaces on a physical interface, the following steps are required:

Configure Frame Relay encapsulation on the physical interface using the encapsulation frame-relay command
For each of the defined PVCs, create a logical subinterface router(config-if)#interface serial number.subinterface-number {multipoint | point-to-point}

To create a subinterface, use the interface serial command. Specify the port number, followed by a period (.), and then by the subinterface number. Usually, the subinterface number is chosen to be that of the DLCI. This makes troubleshooting easier. The final required parameter is stating whether the subinterface is a point-to-point or point-to-multipoint interface. Either the multipoint or point-to-point keyword is required. There is no default. The following commands create the subinterface for the PVC to router B: routerA(config-if)#interface serial 0/0.110 point-to-point If the subinterface is configured as point-to-point, then the local DLCI for the subinterface must also be configured in order to distinguish it from the physical interface. The DLCI is also required for multipoint subinterfaces for which Inverse ARP is enabled. It is not required for multipoint subinterfaces configured with static route maps. The frame-relay interface-dlci command is used to configure the local DLCI on the subinterface router(config-subif)#frame-relay interface-dlci dlci-number Lab Activity Lab Exercise: Configuring Frame Relay Subinterfaces In this lab, the student will configure three routers in a full-mesh Frame Relay network. Web Links Configuring Frame Relay Subinterfaces http://www.cisco.com/en/US/ tech/tk713/tk237/technologies_configuration_ example09186a008009421e.shtml

Content 5.2 Configuring Frame Relay 5.2.6 Verifying the Frame Relay configuration The show interfaces command displays information regarding the encapsulation and Layer 1 and Layer 2 status. It also displays information about the following:

The LMI type
The LMI DLCI
The Frame Relay data terminal equipment/data circuit-terminating equipment (DTE/DCE) type

Normally, the router is considered a data terminal equipment (DTE) device. However, a Cisco router can be configured as a Frame Relay switch. The router becomes a data circuit-terminating equipment (DCE) device when it is configured as a Frame Relay switch. Use the show frame-relay lmi command to display LMI traffic statistics. For example, this command demonstrates the number of status messages exchanged between the local router and the local Frame Relay switch. Use the show frame-relay pvc [interface interface] [dlci] command to display the status of each configured PVC as well as traffic statistics. This command is also useful for viewing the number of BECN and FECN packets received by the router. The PVC status can be active, inactive, or deleted. The show frame-relay pvc command displays the status of all the PVCs configured on the router. Specifying a PVC will show the status of only that PVC. In Figure , the show frame-relay pvc 100 command displays the status of only PVC 100. Use the show frame-relay map command to display the current map entries and information about the connections. The following information interprets the show frame-relay map output that appears in Figure :

100 is the decimal value of the local DLCI number
0x64 is the hex conversion of the DLCI number, 0x64 = 100 decimal
0x1840 is the value as it would appear on the wire because of the way the DLCI bits are spread out in the address field of the Frame Relay frame
10.140.1.1 is the IP address of the remote router, dynamically learned via the Inverse ARP process
Broadcast/multicast is enabled on the PVC
PVC status is active

To clear dynamically created Frame Relay maps, which are created using Inverse ARP, use the clear frame-relay-inarp command. Lab Activity e-Lab Activity: show frame-relay pvc In this activity, the student will demonstrate how to use the show frame-relay pvc command to display statistics about PVCs for Frame Relay interfaces.

Content 5.2 Configuring Frame Relay 5.2.7 Troubleshooting the Frame Relay configuration Use the debug frame-relay lmi command to determine whether the router and the Frame Relay switch are sending and receiving LMI packets properly. The “out” is an LMI status message sent by the router. The “in” is a message received from the Frame Relay switch. “type 0” is a full LMI status message. “type 1” is an LMI exchange. The “dlci 100, status 0x2” means that the status of DLCI 100 is active. The possible values of the status field are as follows:

0x0 – Added/inactive means that the switch has this DLCI programmed but for some reason it is not usable. The reason could possibly be the other end of the PVC is down.
0x2 – Added/active means the Frame Relay switch has the DLCI and everything is operational.
0x4 – Deleted means that the Frame Relay switch does not have this DLCI programmed for the router, but that it was programmed at some point in the past. This could also be caused by the DLCIs being reversed on the router, or by the PVC being deleted by the service provider in the Frame Relay cloud.

Lab Activity e-Lab Activity: Frame Relay Configuration In this activity, the student will work through