
Configuring Dial Services
5-8 114062 Rev. A
This type of network is ideal for an unnumbered demand circuit group because it
supports an extensive number of nodes. If you were to configure each circuit
individually, the task of backing up each remote router would be difficult. By
using demand circuit groups, however, you need only one configuration on the
disaster recovery router to support many remote sites.
The configuration for this type of network is as follows:
• The branch offices are configured for dial backup and are connected directly
to the regional router. They determine if the connection to the regional router
fails and invoke the dial backup connection.
• The circuits on Router 5, the recovery router, are configured as a demand
circuit group, with three circuits in the group. (Router 5 uses an existing
demand pool for the demand circuit group.) These circuits accept calls from
the remote routers configured with dial backup.
The Connection Mode for the circuits in the demand circuit group is set to No
Dial because the recovery router does not initiate connections. The remote
side of the connection must establish the connection first.
• Router 5’s Caller Resolution Table contains entries for Routers 2, 3, and 4.
Each entry specifies the same demand circuit group.
In the example, if any of the branch offices detect a failure of the regional router’s
primary line, they attempt to bring up a dial backup connection by placing a call to
the recovery router. The number of branch offices that successfully connect to the
recovery router depends on the number of circuits in the demand circuit group.
Once the connection is made, data can continue across the network.
Note: Demand circuit groups only work with PPP. You cannot use them in a
network where the dial backup circuits are using Frame Relay.
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