
Configuring Dial Services
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Defining the Role of the Router in the Network
When you configure a router for dial backup, you must specify whether the router
initiates calls or waits to receive calls. The router placing the backup call waits
until the primary circuit fails. The other router waits for the call without trying to
initiate it. If you do not specify the role of each router, each one tries to call the
other simultaneously, and the routers receive busy signals.
You define the role of the router via the Backup Mode parameter, which is part of
the primary circuit configuration (see Chapter 9). Do not configure both sides of
the circuit with the same value.
Bandwidth for Backup Circuits
Time-sensitive protocols or interactive protocols (for example, Telnet) may not
function correctly over a backup circuit that has less bandwidth than the primary
circuit. When user-response time is critical, backup circuits require equal
bandwidth as the primary circuits.
Using Unnumbered Interfaces to Dial an Alternate Site
IP unnumbered interfaces are interfaces on a point-to-point connection for which
you do not configure a specific IP address, for example, 128.185.35.70. Instead,
you configure an address of 0.0.0.0. Unnumbered interfaces are useful because the
router is no longer restricted to a specific IP destination address. This gives the
router the flexibility to dial an alternate site if it cannot reach the original
destination.
If you configure unnumbered IP over a PPP primary circuit and the connection to
the destination router fails, the local router automatically dials each phone number
in the outgoing phone list until it successfully connects to an alternate router.
You can also configure unnumbered interfaces for IPX and bridge protocols;
however, the sample application that follows describes only IP to simplify the
example. For more information about unnumbered interfaces, refer to Configuring
IP Services; Configuring IPX Services; or Configuring Bridging Services.
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