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Cisco IOS Software Releases 12.0 S

Frame Relay Fast Restart

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Frame Relay Fast Restart

Table Of Contents

Frame Relay Fast Restart

Feature Overview

Accelerating the LMI Cycle

Accelerating Inverse ARP

Benefits

Restrictions

Related Documents

Supported Platforms

Supported Standards, MIBs, and RFCs

Configuration Tasks

Enabling Frame Relay Fast Restart on the Router

Enabling Frame Relay Fast Restart on an Interface

Changing the Number of Accelerated LMI Polling Cycles

Verifying Frame Relay Fast Restart

Configuration Examples

Frame Relay Fast Restart Example

Command Reference

frame-relay fast-restart (global)

frame-relay fast-restart (interface)

Glossary


Frame Relay Fast Restart


Feature History

Release
Modification

12.0(18)ST

This feature was introduced on the Cisco 10000 series routers.

12.0(19)ST1

This feature was introduced on the Cisco 7500 series routers.

12.0(22)S

This feature was integrated into Cisco IOS Release 12.0(22)S.


This document describes the Frame Relay Fast Restart feature in Cisco IOS Release 12.0(22)S. It includes the following sections:

Feature Overview

Supported Platforms

Supported Standards, MIBs, and RFCs

Configuration Tasks

Configuration Examples

Command Reference

Feature Overview

The Frame Relay Fast Restart feature increases network availability by reducing recovery time from Route Processor (RP) failures on Cisco 7500 series and Cisco 10000 series routers in Frame Relay networks. This feature reduces recovery time by accelerating the transition from primary RP to standby RP after a hardware or software failure.

When a switchover from primary RP to standby RP occurs on a switch with Frame Relay line cards, the switch must implement an initialization procedure to bring permanent virtual circuits (PVCs) back up and to reestablish dynamic mappings. While this procedure is under way, the Frame Relay interface is unavailable for traffic forwarding. Before the introduction of this feature, the initialization procedure took from 30 to 90 seconds to complete on each Frame Relay interface. The Frame Relay Fast Restart feature reduces interface restart time to 10 to 15 seconds.

The Frame Relay Fast Restart feature uses the methods described in the following sections to reduce interface restart time:

Accelerating the LMI Cycle

Accelerating Inverse ARP

Accelerating the LMI Cycle

To address the possibility that the line protocol is down upon switchover to the standby RP, the Frame Relay Fast Restart feature introduces an accelerated Local Management Interface (LMI) cycle. The accelerated LMI cycle is designed to bring the line protocol up quickly, in turn making PVCs available sooner.

Before the introduction of Frame Relay Fast Restart, LMI polling cycles occurred every 10 seconds, and on the sixth cycle a full LMI status request was sent. This pattern resulted in the sending of a full LMI status request every 60 seconds. With the accelerated LMI cycle, a full status request is sent to the switch immediately after switchover to the standby RP. The next polling cycle begins within 1 second following receipt of the full status from the switch rather than waiting the default 10 seconds. A full status request is also sent at the last polling cycle. The accelerated LMI cycle ends after a fixed number of polling cycles, which can be configured to meet the requirements of the switch.

The accelerated LMI cycle causes the line protocol to come up and PVCs to be reported active in 1 or 2 seconds instead of the 30 to 40 seconds that it would have taken before the introduction of this feature.


Note It may take an additional 10 seconds before the remote router sees that the PVCs are up.



Note The accelerated DTE LMI cycle is nonstandard and may cause problems for some DCE LMI implementations. When the DTE device is directly connected to a Cisco DCE device that is terminating PVCs, the DCE device must be running a Cisco IOS software release based on Cisco IOS Release 12.0(18)ST, 12.0(17.6)S, 12.1(9.1), or 12.2(2.2) or later.


Accelerating Inverse ARP

Inverse Address Resolution Protocol (ARP) requests, where applicable, will be sent out as soon as a PVC becomes active. Before the introduction of the Frame Relay Fast Restart feature, when an Inverse ARP request was unsuccessful, the request was resent every 60 seconds. This new feature accelerates the Inverse ARP timer so that if a request comes back unsuccessful, a second request is sent in 10 seconds. Subsequent requests are sent every 60 seconds.

Benefits

The Frame Relay Fast Restart feature increases network availability by reducing the recovery time from hardware and software failures on Cisco routers in Frame Relay networks. This feature enables PVCs to be available for use within 10 to 15 seconds of switchover to a standby Route Processor; in contrast, before the introduction of this feature, it could take from 30 to 90 seconds.

Restrictions

The Frame Relay Fast Restart feature supports only the following interfaces and connections:

Serial interfaces

DTE LMI type

PVCs (switched and terminated)

Related Documents

Cisco IOS Wide-Area Networking Configuration Guide, Release 12.0

Cisco IOS Wide-Area Networking Command Reference, Release 12.0

Supported Platforms

Cisco 7500 series

Cisco 10000 series

Determining Platform Support Through Feature Navigator

Cisco IOS software is packaged in feature sets that support specific platforms. To get updated information regarding platform support for this feature, access Feature Navigator. Feature Navigator dynamically updates the list of supported platforms as new platform support is added for the feature.

Feature Navigator is a web-based tool that enables you to quickly determine which Cisco IOS software images support a specific set of features and which features are supported in a specific Cisco IOS image.

To access Feature Navigator, you must have an account on Cisco.com. If you have forgotten or lost your account information, send a blank e-mail to cco-locksmith@cisco.com. An automatic check will verify that your e-mail address is registered with Cisco.com. If the check is successful, account details with a new random password will be e-mailed to you. Qualified users can establish an account on Cisco.com by following the directions at http://www.cisco.com/register.

Feature Navigator is updated regularly when major Cisco IOS software releases and technology releases occur. For the most current information, go to the Feature Navigator home page at the following URL:

http://www.cisco.com/go/fn

Supported Standards, MIBs, and RFCs

Standards

No new standards are supported by this feature.

MIBs

No new MIBs are supported by this feature.

To obtain lists of supported MIBs by platform and Cisco IOS release, and to download MIB modules, go to the Cisco MIB website on Cisco.com at http://www.cisco.com/public/sw-center/netmgmt/cmtk/mibs.shtml.

RFCs

No new RFCs are supported by this feature.

Configuration Tasks

See the following sections for configuration tasks for the Frame Relay Fast Restart feature. Each task in the list is identified as either required or optional.

Enabling Frame Relay Fast Restart on the Router (required)

Enabling Frame Relay Fast Restart on an Interface (optional)

Changing the Number of Accelerated LMI Polling Cycles (optional)

Configuration Examples (optional)

Enabling Frame Relay Fast Restart on the Router

To enable Frame Relay Fast Restart on the router, use the following command in global configuration mode:

Command
Purpose

Router(config)# frame-relay fast-restart

Enables Frame Relay fast restart on the router and sets the default number of accelerated polling cycles to be completed to 4 cycles.

Enabling Frame Relay Fast Restart on an Interface

Entering the frame-relay fast-restart command in global configuration mode will enable Frame Relay Fast Restart on all interfaces. Frame Relay Fast Restart can be disabled on individual interfaces using the no frame-relay fast-restart command in interface configuration mode.

To reenable Frame Relay Fast Restart if it was disabled on an interface using the no frame-relay fast-restart command, use the following commands in interface configuration mode:

 
Command
Purpose

Step 1 

Router(config-if)# encapsulation frame-relay

Enables Frame Relay encapsulation.

Step 2 

Router(config-if)# frame-relay fast-restart [poll number-of-cycles]

Enables Frame Relay Fast Restart on the interface. This command can also be used to configure the number of accelerated LMI polling cycles for the interface. The default is 4 cycles. The range is from 1 to 10.

Note In order for Frame Relay Fast Restart to work on an interface, it must be enabled on the router using the frame-relay fast-restart command in global configuration mode.

Changing the Number of Accelerated LMI Polling Cycles

To change the number of accelerated LMI polling cycles that will be completed for an interface, use the following commands in interface configuration mode:

 
Command
Purpose

Step 1 

Router(config-if)# encapsulation frame-relay

Enables Frame Relay encapsulation.

Step 2 

Router(config-if)# frame-relay fast-restart [poll number-of-cycles]

Enables Frame Relay Fast Restart on the interface. This command can also be used to configure the number of accelerated LMI polling cycles for the interface. The default is 4 cycles. The range is from 1 to 10.

Note In order for Frame Relay Fast Restart to work on an interface, it must be enabled on the router using the frame-relay fast-restart command in global configuration mode.

Verifying Frame Relay Fast Restart

To verify the configuration of Frame Relay Fast Restart, use the show running-config command in EXEC mode:

Router# show running-config
Building configuration...

Current configuration : 17801 bytes
!
version 12.0
.
.
.
ip cef distributed
no ip domain-lookup
ip host host1
frame-relay fast-restart <!--indicates frame-relay fast-restart is enabled-->
!
!

Configuration Examples

This section provides the following configuration example:

Frame Relay Fast Restart Example

Frame Relay Fast Restart Example

In the following example, Frame Relay Fast Restart is enabled on the router, and the accelerated LMI poll timer is set to complete 3 polling cycles:

frame-relay fast-restart
interface Serial0/0/0/1:1
 ip address 131.180.60.5 255.255.255.0
 encapsulation frame-relay
 frame-relay fast-restart poll 3
 frame-relay map ip 131.180.60.10 100
 frame-relay intf-type dte

Command Reference

This section documents new commands. All other commands used with this feature are documented in the Cisco IOS Release 12.2 command reference publications.

frame-relay fast-restart (global)

frame-relay fast-restart (interface)

frame-relay fast-restart (global)

To enable Frame Relay Fast Restart functionality on the router, use the frame-relay fast-restart command in global configuration mode. To disable Frame Relay Fast Restart functionality, use the no form of this command.

frame-relay fast-restart

no frame-relay fast-restart

Syntax Description

This command has no arguments or keywords.

Defaults

Frame Relay Fast Restart is not enabled by default.

Frame Relay Fast Restart will complete 4 accelerated LMI cycles by default.

Command Modes

Global configuration

Command History

Release
Modification

12.0(18)ST

This command was introduced on Cisco 10000 series routers.

12.0(19)ST1

This command was introduced on Cisco 7500 series routers.

12.0(22)S

This command was integrated into Cisco IOS Release 12.0(22)S.


Usage Guidelines

Frame Relay fast restart reduces the time needed for permanent virtual circuits (PVCs) to become active and for dynamic mappings to become established after a primary-to-standby Route Processor switchover.

Frame Relay Fast Restart can be disabled on individual interfaces by using the no frame-relay fast-restart command in interface configuration mode.

To configure the number of accelerated Local Management Interface (LMI) polling cycles to be completed when Frame Relay Fast Restart is enabled, use the frame-relay fast-restart command in interface configuration mode. The default number of polling cycles is 4.


Note The frame-relay fast-restart command enables an accelerated DTE Local Management Interface (LMI) cycle that is nonstandard and may cause problems for some DCE LMI implementations. When the DTE device is directly connected to a Cisco DCE device that is terminating PVCs, the DCE device must be running a Cisco IOS software release based on Cisco IOS Release 12.0(19)ST, 12.0(17.6)S, 12.1(9.1), or 12.2(2.2) or later.


Examples

In the following example, Frame Relay Fast Restart is enabled, and the accelerated LMI poll timer is set to complete a minimum of 3 cycles:

frame-relay fast-restart
interface Serial0/0/0/1:1
 ip address 131.180.60.5 255.255.255.0
 encapsulation frame-relay
 frame-relay fast-restart poll 3
 frame-relay map ip 131.180.60.10 100
 frame-relay intf-type dte

The following example shows Frame Relay Fast Restart enabled on the router but disabled on serial interface 0/0/0/1:1:

frame-relay fast-restart
interface Serial0/0/0/1:1
 no frame-relay fast-restart

Related Commands

Command
Description

frame-relay fast-restart (interface)

Enables Frame Relay Fast Restart functionality on the interface and configures the number of accelerated LMI polling cycles.


frame-relay fast-restart (interface)

To enable Frame Relay Fast Restart functionality on the interface and to configure the number of accelerated Local Management Interface (LMI) polling cycles, use the frame-relay fast-restart command in interface configuration mode. To disable Frame Relay Fast Restart functionality on the interface, use the no form of this command.

frame-relay fast-restart [poll number-of-cycles]

no frame-relay fast-restart

Syntax Description

poll number-of-cycles

(Optional) Number of accelerated LMI polling cycles. The range is from 1 to 10.


Defaults

4 cycles

Command Modes

Interface configuration

Command History

Release
Modification

12.0(18)ST

This command was introduced on Cisco 10000 series routers.

12.0(19)ST1

This command was introduced on Cisco 7500 series routers.

12.0(22)S

This command was integrated into Cisco IOS Release 12.0(22)S.


Usage Guidelines

Frame Relay Fast Restart reduces the time needed for permanent virtual circuits (PVCs) to become active and for dynamic mappings to become established after a primary-to-standby Route Processor switchover.

Frame Relay Fast Restart will not work unless it has been enabled on the router by using the frame-relay fast-restart command in global configuration mode.

Frame Relay Fast Restart uses an accelerated LMI cycle in which a full status request is sent to the switch immediately after switchover to the standby Route Processor. The next polling cycle begins within 1 second following receipt of the full status from the switch. A full status request is also sent at the last polling cycle. You can use the frame-relay fast-restart command in interface configuration mode to configure the number of polling cycles that will be completed.

To reset the number of accelerated LMI polling cycles to the default setting, use the frame-relay fast-restart command in interface configuration mode.

Examples

The following example configures LMI to complete 6 accelerated polling cycles:

interface Serial0/0/0/1:1
 ip address 131.180.60.5 255.255.255.0
 encapsulation frame-relay
 frame-relay fast-restart poll 6

Related Commands

Command
Description

frame-relay fast-restart (global)

Enables Frame Relay Fast Restart functionality on the router.


Glossary

DTE—data terminal equipment. Device at the user end of a user-network interface that serves as a data source, destination, or both. DTE connects to a data network through a data communications equipment (DCE) device (for example, a modem) and typically uses clocking signals generated by the DCE. DTE includes such devices as computers, protocol translators, and multiplexers.

Inverse ARP—Inverse Address Resolution Protocol. Method of building dynamic routes in a network. Allows an access server to discover the network address of a device associated with a virtual circuit.

LMI—Local Management Interface. Set of enhancements to the basic Frame Relay specification. LMI includes support for a keepalive mechanism, which verifies that data is flowing; a multicast mechanism, which provides the network server with its local data-link connection identifier (DLCI) and the multicast DLCI; global addressing, which gives DLCIs global rather than local significance in Frame Relay networks; and a status mechanism, which provides an ongoing status report on the DLCIs known to the switch.

PVC—permanent virtual circuit. Virtual circuit that is permanently established. PVCs save bandwidth associated with circuit establishment and teardown in situations where certain virtual circuits must exist all the time.

RP—Route Processor. Processor module that contains the CPU, system software, and most of the memory components that are used in the router.