
Configuring Dial Services
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308621-14.00 Rev 00
Configuring Standby Circuits
A standby circuit is a type of demand circuit that gives the router another path to
the destination. The destination can be a different interface at the primary circuit’s
original site or an entirely different site.
Standby circuits can be configured for asynchronous (RS-449), synchronous
(RS-449, V.35, RS-422, and X.21), and ISDN interfaces. PPP is the only layer 2
protocol that you can configure over a standby circuit; you cannot use frame relay.
Guidelines for Configuring Standby Circuits
A standby circuit must be configured at the central site and at the remote site.
When setting up a standby circuit, follow these guidelines:
• Configure one side of the connection to initiate calls (the hot standby circuit).
This is the outgoing side of the connection.
• Configure one side of the connection to receive calls (the standby circuit).
This is the incoming side of the connection.
If the standby circuit is part of a bandwidth-on-demand configuration, the
outgoing side should be the monitor router, and the incoming side should be
the non-monitor router.
• If you configure routing protocols on the standby circuit, the Inactivity
Timeout parameter does not work. When the router brings up the standby
circuit, the routing protocols keep the connection active.
• Configure the time of day schedules and the failback timers only on the hot
standby side of the connection.
• Use CHAP or PAP as the authentication protocol for the circuit.
• If you want to use unnumbered interfaces, configure them on the outgoing hot
standby circuit, and configure unnumbered demand circuit groups on the
incoming standby circuit.
For more information about standby demand circuits, see Chapter 6,
“Dial-on-Demand Implementation Notes.”
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