Frame relay Configuration

Enabling Frame Relay Encapsulation on an Interface

To enable Frame Relay encapsulation on the interface level, use the following commands beginning in global configuration mode:

	Command	Purpose
Step 1	Router(config)# interface type number	Specifies the interface, and enters interface configuration mode.
Step 2	Router(config-if)# encapsulation frame-relay [ietf]	Enables and specifies the Frame Relay encapsulation method.

Frame Relay supports encapsulation of all supported protocols in conformance with RFC 1490, allowing interoperability among multiple vendors. Use the Internet Engineering Task Force (IETF) form of Frame Relay encapsulation if your router or access server is connected to another vendor's equipment across a Frame Relay network. IETF encapsulation is supported either at the interface level or on a per-VC basis.

Shut down the interface prior to changing encapsulation types. Although shutting down the interface is not required, it ensures that the interface is reset for the new encapsulation.

For an example of enabling Frame Relay encapsulation on an interface, see the section "IETF Encapsulation Examples" later in this chapter.

Configuring Dynamic or Static Address Mapping

Dynamic address mapping uses Frame Relay Inverse ARP to request the next-hop protocol address for a specific connection, given its known DLCI. Responses to Inverse ARP requests are entered in an address-to-DLCI mapping table on the router or access server; the table is then used to supply the next-hop protocol address or the DLCI for outgoing traffic.

Inverse ARP is enabled by default for all protocols it supports, but can be disabled for specific protocol-DLCI pairs. As a result, you can use dynamic mapping for some protocols and static mapping for other protocols on the same DLCI. You can explicitly disable Inverse ARP for a protocol-DLCI pair if you know that the protocol is not supported on the other end of the connection. See the section "Disabling or Reenabling Frame Relay Inverse ARP" later in this chapter for more information.

See the following sections for further details on configuring dynamic or static address mapping:

•Configuring Dynamic Address Mapping

•Configuring Static Address Mapping

Configuring Dynamic Address Mapping

Inverse ARP is enabled by default for all protocols enabled on the physical interface. Packets are not sent out for protocols that are not enabled on the interface.

Because Inverse ARP is enabled by default, no additional command is required to configure dynamic mapping on an interface.

Configuring Static Address Mapping

A static map links a specified next-hop protocol address to a specified DLCI. Static mapping removes the need for Inverse ARP requests; when you supply a static map, Inverse ARP is automatically disabled for the specified protocol on the specified DLCI.

You must use static mapping if the router at the other end either does not support Inverse ARP at all or does not support Inverse ARP for a specific protocol that you want to use over Frame Relay.

To establish static mapping according to your network needs, use one of the following commands in interface configuration mode:

Command	Purpose
Router(config-if)# frame-relay map protocol protocol-address dlci [broadcast] [ietf] [cisco]	Maps between a next-hop protocol address and DLCI destination address.
Router(config-if)# frame-relay map clns dlci [broadcast]	Defines a DLCI used to send ISO CLNS frames.
Router(config-if)# frame-relay map bridge dlci[broadcast] [ietf]	Defines a DLCI destination bridge.

The supported protocols and the corresponding keywords to enable them are as follows:

•IP—ip

•DECnet—decnet

•AppleTalk—appletalk

•XNS—xns

•Novell IPX—ipx

•VINES—vines

•ISO CLNS—clns

You can greatly simplify the configuration for the Open Shortest Path First (OSPF) protocol by adding the optional broadcast keyword when doing this task. Refer to the frame-relay map command description in the Cisco IOS Wide-Area Networking Command Reference and the examples at the end of this chapter for more information about using the broadcast keyword.

For examples of establishing static address mapping, refer to the section "Static Address Mapping Examples" later in this chapter.

Configuring the LMI

Beginning with Cisco IOS Release 11.2, the software supports Local Management Interface (LMI) autosense, which enables the interface to determine the LMI type supported by the switch. Support for LMI autosense means that you are no longer required to configure the LMI explicitly.

See the following sections for further details on configuring the LMI:

•Activating LMI Autosense

•Explicitly Configuring the LMI

For information on using Enhanced Local Management Interface with traffic shaping, see the section "Configuring Frame Relay Traffic Shaping" later in this chapter.

For an example of configuring the LMI, see the section "Pure Frame Relay DCE Example" later in this chapter.

Activating LMI Autosense

LMI autosense is active in the following situations:

•The router is powered up or the interface changes state to up.

•The line protocol is down but the line is up.

•The interface is a Frame Relay DTE.

•The LMI type is not explicitly configured.

See the following sections for additional information concerning activating LMI autosense:

•Status Request

•Status Messages

•LMI Autosense

•Configuration Options

Status Request

When LMI autosense is active, it sends out a full status request, in all three LMI types, to the switch. The order is ANSI, ITU, cisco, but it is done in rapid succession. Cisco IOS software provides the ability to listen in on both DLCI 1023 (cisco LMI) and DLCI 0 (ANSI and ITU) simultaneously.

Status Messages

One or more of the status requests will elicit a reply (status message) from the switch. The router will decode the format of the reply and configure itself automatically. If more than one reply is received, the router will configure itself with the type of the last received reply. This is to accommodate intelligent switches that can handle multiple formats simultaneously.

LMI Autosense

If LMI autosense is unsuccessful, an intelligent retry scheme is built in. Every N391 interval (default is 60 seconds, which is 6 keep exchanges at 10 seconds each), LMI autosense will attempt to ascertain the LMI type. For more information about N391, see the frame-relay lmi-n391dte command in the chapter "Frame Relay Commands" in the Cisco IOS Wide-Area Networking Command Reference.

The only visible indication to the user that LMI autosense is under way is that debug frame lmi is turned on. At every N391 interval, the user will now see three rapid status inquiries coming out of the serial interface: one in ANSI, one in ITU, and one in cisco LMI-type.

Configuration Options

No configuration options are provided; LMI autosense is transparent to the user. You can turn off LMI autosense by explicitly configuring an LMI type. The LMI type must be written into NVRAM so that next time the router powers up, LMI autosense will be inactive. At the end of autoinstall, a frame-relay lmi-type xxx statement is included within the interface configuration. This configuration is not automatically written to NVRAM; you must explicitly write the configuration to NVRAM by using the copy system:running-config or copy nvram:startup-config command.

Explicitly Configuring the LMI

Frame Relay software supports the industry-accepted standards for addressing the LMI, including the Cisco specification. If you want to configure the LMI and thus deactivate LMI autosense, perform the tasks in the following sections:

•Setting the LMI Type (Required)

•Setting the LMI Keepalive Interval (Required)

Setting the LMI Type

If the router or access server is attached to a public data network (PDN), the LMI type must match the type used on the public network. Otherwise, the LMI type can be set to suit the needs of your private Frame Relay network.

You can set one of the following three types of LMIs on Cisco devices: ANSI T1.617 Annex D, Cisco, and ITU-T Q.933 Annex A. To do so, use the following commands beginning in interface configuration mode:

	Command	Purpose
Step 1	Router(config-if)# frame-relay lmi-type {ansi | cisco |q933a}	Sets the LMI type.
Step 2	Router# copy nvram:startup-config destination	Writes the LMI type to NVRAM.

For an example of setting the LMI type, see the section "Pure Frame Relay DCE Example" later in this chapter.

Setting the LMI Keepalive Interval

A keepalive interval must be set to configure the LMI. By default, this interval is 10 seconds and, according to the LMI protocol, must be less than the corresponding interval on the switch. To set the keepalive interval, use the following command in interface configuration mode:

Command	Purpose
Router(config-if)# keepalive number	Sets the LMI keepalive interval.

To disable keepalives on networks that do not utilize LMI, use the no keepalive interface configuration command. For an example of how to specify an LMI keepalive interval, see the section "Two Routers in Static Mode Example" later in this chapter.