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Table Of Contents
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
Frame Relay Fast Restart Example
frame-relay fast-restart (global)
frame-relay fast-restart (interface)
Frame Relay Fast Restart
First Published: 12.0(18)STLast Updated: February 28, 2006The 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.
History for the Frame Relay Fast Restart Feature
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Contents
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
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
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:
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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.
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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:
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:
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:
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-configBuilding configuration...Current configuration: 17801 bytes!version 12.0...ip cef distributedno ip domain-lookupip host host1frame-relay fast-restart <!--indicates frame-relay fast-restart is enabled-->!!Configuration Examples
This section provides the following configuration example:
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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-restartinterface Serial0/0/0/1:1ip address 192.168.60.5 255.255.255.0encapsulation frame-relayframe-relay fast-restart poll 3frame-relay map ip 192.168.60.10 100frame-relay intf-type dteAdditional References
The following sections provide references related to Frame Relay Fast Restart.
Related Documents
Standards
MIBs
None
To locate and download MIBs for selected platforms, Cisco IOS releases, and feature sets, use Cisco MIB Locator found at the following URL:
RFCs
Technical Assistance
Command Reference
This section documents modified commands only.
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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
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.
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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-restartinterface Serial0/0/0/1:1ip address 192.168.60.5 255.255.255.0encapsulation frame-relayframe-relay fast-restart poll 3frame-relay map ip 192.168.60.10 100frame-relay intf-type dteThe following example shows Frame Relay Fast Restart enabled on the router but disabled on serial interface 0/0/0/1:1:
frame-relay fast-restartinterface Serial0/0/0/1:1no frame-relay fast-restartRelated Commands
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
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 Serial0/0/0/1:1ip address 192.168.60.5 255.255.255.0encapsulation frame-relayframe-relay fast-restart poll 6Related Commands
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.
Any Internet Protocol (IP) addresses used in this document are not intended to be actual addresses. Any examples, command display output, and figures included in the document are shown for illustrative purposes only. Any use of actual IP addresses in illustrative content is unintentional and coincidental.
© 2001, 2006 Cisco Systems, Inc. All rights reserved.
