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Frame Relay is a method of encapsulating network information that allows for fast delivery and high line utilization. PortMaster routers support Frame Relay over synchronous ports.
This chapter uses an example to demonstrate how to configure the PortMaster to connect to a synchronous line using Frame Relay. This chapter also explains how to configure Frame Relay subinterfaces
The following topics are discussed:
Synchronous ports on PortMaster products can be configured to support Frame Relay connections. As opposed to a dedicated or leased line, a Frame Relay connection can be thought of as a virtual switch.
Frame Relay is a switched digital service that supports multiple virtual circuits, simultaneously connected to a site by a single physical circuit. Each site requires only one physical circuit into the Frame Relay network-usually referred to as a cloud-but can have several virtual circuits to reach other sites attached to the cloud.
PortMaster products support permanent virtual circuits (PVCs). PVCs are used to form a connection between any two devices attached to a Frame Relay cloud. Each PVC is given a unique number on each physical circuit along the path between the two devices. This unique number is called a data link connection identifier (DLCI). The DLCI is automatically changed to the PVC number of the next physical circuit as it passes through each switch along the path. A DLCI is different from a network address because it identifies a circuit in both directions, not a particular endpoint. A frame contains only one DLCI, not a source and destination.
In general, the only DLCI numbers you see are those numbers assigned to the physical circuits on the perimeter of the Frame Relay cloud.
The physical circuit between point A and the network must be ordered with a certain line speed. This speed is the physical maximum bandwidth for your connection to the Frame Relay network. Expansion beyond this limit is not possible without a hardware change and a new circuit installation.
The connection into the telecommunications provider's Frame Relay network must be ordered at a particular port speed, which is the maximum bandwidth rate that the telecommunications provider accepts from your connection. This number must be less than or equal to the line speed. This speed is the maximum rate at which you can transmit data to any of your PVCs under any circumstances. The port speed differs from line speed only in that it can be upgraded through software without a circuit installation or hardware change.
Each PVC has a property known as committed information rate (CIR), which represents the guaranteed minimum bandwidth available to the particular PVC under all conditions. In some implementations, an additional property can be assigned to a PVC, known as "burst speed" or "maximum burst." This speed represents the highest rate at which data is allowed to flow over a given PVC, regardless of bandwidth availability.
The PortMaster pushes as much data out of the serial port as it can at port speed for any PVC that has traffic, regardless of CIR. The Frame Relay switch passes as much of the data as possible on to the next link. However, once a particular PVC has transmitted its CIR-worth of bits each second, the switch marks any additional frames as "discard eligible." If the switch receives more frames than it can pass along, the frames are automatically discarded in the following order:
In general, when ordering Frame Relay service for a private network, order large-bandwidth physical circuits (T1) with port speed appropriate to your application, and a CIR that is high enough to provide minimally acceptable performance for your application. In most cases, ordering according to these criteria provides service that is close to your port speed. The CIR is a guaranteed minimum throughput, not a maximum limit. Port speed is the maximum limit.
The following Frame Relay terms relate to network management. The Frame Relay specification supports automatic network status updates, which are exchanged between adjacent devices in the Frame Relay network. These status updates are known as the Local Management Interface (LMI). Two forms of LMI are available in the Portmaster: Cisco/Stratacom LMI, which is commonly referred to as LMI, and ANSI T1.617 Annex D LMI, which is commonly referred to as Annex-D.
Generally, your telecommunications provider offers three LMI options for your physical circuit: LMI, Annex-D, or none. Because LMI exists only between your router and the switch to which your physical circuit connects, it does not need to match what the remote ends of your PVCs are using. However, your circuit LMI must match the configuration on your PortMaster. Generally, Annex-D is recommended, because it is a more feature-rich and robust version of LMI.
You configure Frame Relay by selecting the Frame Relay protocol, setting the IP address of the port, and specifying the DLCIs during the synchronous port configuration.
Alternatively, the PortMaster can discover DLCIs dynamically with LMI or Annex-D and learn the IP addresses of the other routers through Inverse ARP if the other routers on your Frame Relay cloud support Inverse ARP as specified in RFC 1490. In this configuration, the PortMaster sends an LMI status request every 10 configurable seconds by default. Every sixth request is a full status request, and the others are keepalives. In this configuration, the port state is CONNECTING until it receives three replies from the switch; then the port state becomes ESTABLISHED. After six unanswered requests, the PortMaster resets the port.
Figure 13-1 shows an example of a Frame Relay connection.
Note ¯ 
All synchronous ports require an external clock signal to regulate the port speed.
Frame Relay Configuration
You can specify whether the PortMaster accepts Local Management Interface (LMI) frames from the attached Frame Relay switch. If LMI is enabled on the switch, you must enable LMI on the PortMaster. The default keepalive value is 10 seconds. However, if your telephone company chooses another keepalive value, change this value as they instruct you. Enabling LMI causes the DLCI list to be completed automatically. If the attached switch uses an interval keepalive timer different from the Frame Relay default, be sure the keepalive timer on the PortMaster matches that of the attached switch.
Note ¯ 
Contact your Frame Relay carrier to determine which keepalive they are using, LMI or Annex-D.
To enable LMI, use the following command:
The PortMaster also accepts the Annex-D polling interval. The Annex-D default value is 10 seconds. However, if your telephone company chooses another keepalive value, change this value as they instruct you. Enabling LMI causes the DLCI list to be completed automatically. Setting the keepalive value to 0 (zero) seconds, or enabling LMI, disables Annex-D.
Note ¯ 
Contact your Frame Relay carrier to determine which keepalive they are using, LMI or Annex-D.
To enable Annex-D, use the following command:
If LMI or Annex-D is not used, you must enter the DLCI list manually. The DLCI list is a list of DLCIs that are accessible through the Frame Relay network by this interface. The PortMaster uses Inverse ARP to learn the IP addresses of routers attached to the PVCs represented by the specified DLCIs, if those routers support Inverse ARP. Alternatively, you can specify IP addresses by appending a colon (:) and IP address after the DLCI.
The DLCI list can be provided by your Frame Relay carrier. For dynamically learned lists, 32 PVCs are allowed. Only 16 PVCs can be specified if the DLCI and IP address are entered. If you specify only DLCIs, you can list 24. When the PVC and IP address are specified, the PortMaster statically configures these entries into its ARP table.
To enter the DLCI list manually, use the following command:
For information on Frame Relay subinterfaces see "Frame Relay Subinterfaces" on page 13-13.
The example described in this chapter connects a PortMaster router located in a main office (Bangkok) with a PortMaster router located in a branch office (New York) using Frame Relay on a synchronous interface.
To install your PortMaster, follow the instructions in the hardware installation guide. If you need additional help, refer to the troubleshooting chapter of the guide. The example in this chapter shows variables in italics. Change these values to reflect your network.
Once you have assigned an IP address to the PortMaster, continue with the following steps:
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Configure the following settings for the PortMaster in Bangkok:
a. Configure global settings (page 13-8).
b. Configure Ethernet interface settings (page 13-8).
c. Configure synchronous port settings (page 13-9).
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Configure the following settings for the PortMaster in New York:
a. Configure Ethernet interface settings (page 13-10).
b. Configure synchronous WAN port settings (page 13-10).
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Troubleshoot the configuration (page 13-12).
You can additionally configure Frame Relay subinterfaces.
Note ¯ 
You must configure the Ethernet interface before configuring the PortMaster for a Frame Relay connection. Refer to Chapter 4, "Configuring the Ethernet Interface," for more information.
Configure the settings for the PortMaster in Bangkok with the values in the following sections.
Configure the global settings on the PortMaster in Bangkok to the values shown in Table 13-1.
Once you have configured the global settings shown in Table 13-1, save the configuration by using the following command:
For more information about global parameters, refer to Chapter 3, "Configuring Global Settings."
Configure the Ethernet interface settings on the PortMaster in Bangkok to the values shown in Table 13-2.
Once you have configured the Ethernet interface as shown in Table 13-2, save the configuration using the following command:
For more information on Ethernet parameters, refer to Chapter 4, "Configuring the Ethernet Interface."
Configure the synchronous WAN port W1 to the values shown in Table 13-3.
Once you have configured the synchronous WAN port as shown in Table 13-3, reset the port and save the configuration using the following commands:
For more information on synchronous ports, refer to Chapter 6, "Configuring a Synchronous WAN Port."
Configure the settings for the PortMaster in New York with the values in the following sections. You do not need to specify a gateway for the PortMaster in New York because it is on the Internet.
Configure the Ethernet interface settings to the values shown in Table 13-4
.
Once you have configured the Ethernet interface as shown in Table 13-4, save the configuration using the following command:
For more information on Ethernet parameters, refer to Chapter 4, "Configuring the Ethernet Interface."
Configure the synchronous WAN port W1 to the values shown in Table 13-5.
Once you have configured the synchronous WAN port as shown in Table 13-5, reset the port and save the configuration using the following commands:
If LMI or Annex-D is set, the PortMaster receives DLCI information in the full status update messages from the Frame Relay switch. The PortMaster then attempts to discover IP addresses of other routers using Inverse ARP. You can set DLCI lists statically as well. The show arp frm1 command lists both the static and dynamic DLCI lists for the S1 port.
If Annex-D is available from your carrier for a new connection, it is preferable to LMI.
To connect to Cisco routers using Frame Relay, the Cisco router must be set to use encapsulation frame-relay ietf for the serial interface; otherwise, the Cisco frame-relay map command for your DLCI must have the ietf keyword appended.
For more information about synchronous ports, refer to Chapter 6, "Configuring a Synchronous WAN Port."
Most synchronous configurations come up with very little trouble if you have configured the PortMaster using information from your carrier. If you are having problems, use the information in this section to debug your configuration.
If you are having trouble with a Frame Relay connection, do the following:
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Once you have verified that the proper keepalives are being received, use the
following commands to turn off the debug utility:
PortMaster routers support a feature called DLCI bundling to allow the splitting of one synchronous port with multiple DLCIs into a maximum of 32 Frame Relay subinterfaces. In this configuration, the DLCIs are divided between the subinterfaces through the use of the location table and the DLCI table. Each subinterface must have its own subnet or assigned network. The PortMaster has a limit of 512 total active interfaces, which can be further limited by available memory.
The port you are configuring must be set for network hardwired use and Frame Relay, and must be in the same dial group as the location.
Use the following commands to configure a Frame Relay subinterface.
To configure a Frame Relay subinterface, you add a location for each interface, configure it with the frame protocol, and associate it with a dial group. Then associate a synchronous port with the same dial group. For example, to create a location called sub1, use the following commands:
The rest of the location table entries are set as described in Chapter 8, "Configuring Dial-Out Connections," including setting an IP address, routing, and filtering for each interface.
The next step in configuring the subinterfaces is to create an entry in the DLCI table. Entries can be followed with an optional IP address or hostname. The keyword ipxdlci is available for IPX networks.
To create a DLCI table entry for the subinterface sub1, use the following commands:
To remove an entry, use the delete command as follows:
DLCI entries that are added or deleted are linked to the location table. Use the show location Locname command to display the DLCI entries.
Packets received on a subinterface can be identified as belonging to that subinterface only if the DLCI is properly entered in the DLCI table for that location. If you are having problems, do the following:
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Once you have verified that the proper keepalives are being received, use the
following commands to turn off the debug utility:
This set of example commands configures a PortMaster IRX-111 router with Frame Relay packets coming into port S1 with DLCIs 16, 17, and 18. Port S1 has already been configured for Frame Relay, so that portion is not shown here. The following commands split the Frame Relay port into a primary subinterface for DLCI 18 and a secondary subinterface for DLCIs 16 and 17.
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