Using and Configuring Features Version 3.3

Using WAN Restoral

This chapter includes the following sections:

"Overview for WAN Restoral, WAN Reroute, and Dial-on-Overflow"
"Before You Begin"
"Configuration Procedure for WAN Restoral"
"Secondary Dial Circuit Configuration"

Overview for WAN Restoral, WAN Reroute, and Dial-on-Overflow

The WAN Restoral, WAN Reroute, and Dial-on-overflow features have similar functions and might be confused. This overview is intended to help you decide which of these functions will be useful to you and to help you find the information you need to configure them.

The configuration commands for all three features are included in the "Configuring WAN Restoral" chapter. For additional information about WAN Reroute and Dial-on-overflow see "The WAN Reroute Feature".

WAN Restoral

WAN Restoral is the most basic function. When you use WAN Restoral, you configure a primary and a secondary link. In case the primary link fails, the secondary link is started and assumes the characteristics of the primary. You don't configure any protocol definitions on the secondary link because it uses the protocol definitions from the primary link.

For WAN Restoral:

There is a pairing between a primary and a secondary link.
You can configure only one primary to use a specific secondary link.
You don't configure protocol definitions (for example: protocol addresses) on the secondary link.
The primary link can be a PPP serial interface or a multilink PPP interface. It can not be a PPP dial circuit interface.
The secondary link must be a PPP dial circuit or a multilink PPP interface.
You must enable the WRS feature using the enable wrs command.
You must enable the primary/secondary pair using the enable secondary-circuit command.

Note:

When BRS is configured on a primary link and the primary link is part of a primary-secondary pair for WAN Restoral, you must configure BRS on the secondary link. Typically when WAN Restoral is configured, the secondary link takes the identify of the primary link. However, this is not true for BRS; therefore, BRS needs to be configured on both the primary and secondary link.

WAN Reroute

WAN Reroute is a more advanced function. When you use WAN Reroute, you configure a primary and an alternate link. In case the primary link fails, the alternate link is started. The routing protocols (for example, RIP or OSPF) detect the newly available link and adjust the routes that are used for forwarding packets.

For WAN Reroute:

There is a pairing between a primary and an alternate link.
You may configure multiple primary links to use the same alternate link.
You must configure protocol definitions on the alternate link.
The primary link may be any link on which you can configure routable protocols (e.g. IP, IPX). For example, the primary link may be a LAN interface, a PPP, Frame Relay, or X.25 serial interface, or a PPP or Frame Relay dial circuit. The following are examples of interface types that cannot be primary links: SDLC serial interfaces, SRLY serial interfaces, and base nets like V.25bis and ISDN.
The alternate link may be any link on which you can configure routable protocols (e.g. IP, IPX) and the datalink type of the alternate link need not match the datalink type of the primary link. For example, the alternate link may be a LAN interface, a PPP, Frame Relay, or X.25 serial interface, or a PPP or Frame Relay dial circuit. The following are examples of interface types that cannot be alternate links: SDLC serial interfaces, SRLY serial interfaces, and base nets like V.25bis and ISDN.
If the primary link is a dial circuit, then it cannot be a dial-on-demand dial circuit. To configure the dial circuit so that it is not a dial-on-demand circuit, you must configure it with set idle 0 at that dial Circuit Config> prompt. Refer to "Configuring and Monitoring Dial Circuits" in the Software User's Guide for more information.
I.430, I.431 and Channelized T1/E1 dial circuits are implicitly fixed, and therefore can be used as a WRS primary.
Note: I.430/I.431 and Channelized T1/E1 dial circuits can be used as WRS primary without any explicit configuration.
The alternate link cannot be a dial-on-demand dial circuit (you must configure set idle 0 on the dial circuit).
You must enable the WRS feature using the enable wrs command.
You must enable the primary/alternate pair using the enable alternate-circuit command.
You may optionally configure stabilization times, routing-stabilization times, and start-and stop-time-of-day-revert-back times to control the switching back to the primary link.
If the alternate link is X.25, you should use the national-personality set disconnect-procedure active command when configuring the X.25 interface of the router that has WAN Reroute enabled and use the national-personality set disconnect-procedure passive command when configuring the X.25 interface of the other router.

Dial-on-overflow

Dial-on-overflow is similar to WAN Reroute, but does not require failure of the primary to start the alternate link. Instead, the utilization of the primary link is monitored, and if a threshold is exceeded, the alternate link is started. Also, not all protocols are brought up on the alternate link. Only IP is brought up on the alternate link, and other protocols continue to use the primary link unless the primary link goes down.

If the primary link goes down, WAN Reroute takes over and any protocols configured on the alternate interface can start detecting and using routes on the alternate interface.

For Dial-on-overflow:

Dial-on-overflow uses the primary/alternate pairing of a WAN Reroute pair.
You must configure a WAN reroute pair to use Dial-on-overflow, and all the restrictions of WAN Reroute configuration apply.
The primary link of a WAN Reroute pair that will be used for Dial-on-overflow must be Frame Relay.
You must use the OSPF routing protocol to use Dial-on-overflow.
You must use the enable dial-on-overflow command to configure add-threshold and drop-threshold, the bandwidth monitoring interval, and the minimum alternate up time.
Stabilization times, routing-stabilization times, and start-time-of-day-revert-back and stop-time-of-day-revert-back times do not affect the operation of dial-on-overflow.

For more information about WAN Reroute see "The WAN Reroute Feature".

Before You Begin

Before you configure WAN Restoral, you must have the following:

A primary serial interface (leased line) configured for PPP. You can use any serial interface on the router.
An interface with the associated dial circuits configured on the router. You can use an ISDN interface, a V.25bis interface, or V.34 interface as the base net.
A secondary dial circuit configured to dial when the primary interface goes down. To configure a dial circuit to do this, set the idle timer to zero using the set idle command at that dial Circuit Config>prompt. This command prevents the dial circuit from being dial-on-demand.
A secondary dial circuit at one end of the link configured to send calls only. Use the set calls outbound command at the Circuit Config> prompt.
Note: Do not configure any protocol addresses on the secondary interface. The protocol assignments for the primary interface are used on the secondary link (dial circuit) when it is active.
A secondary dial circuit at the other end of the link configured to receive calls only. Use the set calls inbound command at the Circuit Config> prompt.

Configuration Procedure for WAN Restoral

This section describes the steps required to configure WAN Restoral. Before you begin, use the list device command at the Config> prompt to list the interface numbers of different devices.

Follow these steps to configure WAN Restoral on the router:

Display the WRS Config> prompt by entering the feature wrs command at the Config> prompt. For example:
```
     Config>feature wrs
     WAN Restoral user configuration
     WRS Config>
```

Assign a secondary dial circuit to the primary interface. This dial circuit will back up the primary interface. For example:

     WRS Config>add secondary-circuit
     Secondary interface number  [0]? 3
     Primary interface number  [0]? 1

Enable WAN Restoral on the secondary dial circuit that you added. For example:

     WRS Config>enable secondary-circuit
     Secondary interface number  [0]? 3

Globally enable WAN Restoral on the router. For example:
```
WRS Config>enable wrs
```
Restart the router for configuration changes to take effect.

Secondary Dial Circuit Configuration

To configure a dial circuit:

Determine the dial-circuit interface number: To do this, type:

Config> list device

If no PPP dial-circuit interface is listed, add a dial-circuit interface by typing:

Config> add device dial-circuit
 
Adding device as interface 3
Defaulting Data-link protocol to PPP
Use "net 3" command to configure circuit parameters

Configure the secondary interface (dial circuit) to have the same datalink type as the primary interface (PPP) from the Config> prompt as follows:
```
Config> set data PPP
Interface Number [0]? 3
```
Access the dial circuit configuration prompt (Circuit Config>) by entering network interface#.
```
Config> network 3
```
Select the base net interface for the dial circuit. The base net can be V.25bis, ISDN, or V.34.
```
Circuit Config> set net 2
```
Set the dial circuit idle timer to 0 (0=fixed) as follows:
```
Circuit Config> set idle 0
```
Set one end of the backup connection to receive calls (for example, router A) as follows:
```
Circuit Config> set calls inbound
```
Set the other end of the backup connection to initiate calls (for example, router B) as follows:
```
Circuit Config> set calls outbound
```

Notes:

Do not use the set calls both command. Setting these individually will help prevent the collisions of incoming and outgoing connection attempts.
Do not configure any forwarder (for example, IP, IPX, etc.) addresses on the dial circuit. The protocol assignments for the primary interface are used on the secondary interface (dial circuit) when it is active.
For ISDN configuration instructions, see "Using the ISDN Interface" in Software User's Guide.
For V.25bis configuration instructions, see "Using the V.25bis Interface" in Software User's Guide.
For V.34 configuration instructions, see "Using the V.34 Interface" in Software User's Guide.

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