
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 then waits for the call without
trying to initiate one. If you do not specify the role of each router, they try to call
one another simultaneously and each router receives a busy signal.
You define the role of a router using the Backup Mode parameter, which is part of
the primary circuit configuration (see Chapter 10). Do not specify the same value
for both sides of the circuit.
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 the same
bandwidth as the primary circuits.
Using Unnumbered Interfaces to Dial an Alternative Site
IP unnumbered interfaces define 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 another 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 another router.
You can also configure unnumbered interfaces for IPX and bridging; however, the
sample network 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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