Cisco 1721 - Manual (Page 84)

Appendix D Ordering and Configuring an ISDN Line
ISDN Configuration Options
D-6
Cisco 1721 Router Hardware Installation Guide
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When the router connects to the service provider’s central office ISDN switch, it
sends the SPIDs to the switch. If the router is not configured with the correct
SPIDs, it cannot place or receive calls. Use the isdn spid command to define the
SPID and the LDN on the router for both ISDN BRI B channels, as follows:
Router(config-if)# isdn spid1 spid-number [ldn]
Router(config-if)# isdn spid2 spid-number [ldn]
Note Although the LDN is usually optional, it might be required so that the router
answers calls made to the second directory number.
ISDN Configuration Options
For information on how to configure Cisco 1721 router to dial in to a central-site
router over ISDN, refer to the Cisco 1700 Router Software Configuration Guide.
For more advanced information on configuring ISDN for Cisco 1700 routers,
refer to the chapter “Configuring ISDN” in the Dial Solutions Configuration
Guide, which is on the Documentation CD-ROM that came with your router. This
document includes information on the following topics:
• Snapshot Routing
• Dial-on-Demand Routing
• Bandwidth on Demand and Dial Backup
Snapshot Routing
You can configure snapshot routing for the router ISDN interface. During
snapshot routing, the router is configured to bring up the ISDN line, to
dynamically learn about remote routes, and then to take down the ISDN line. The
router saves the learned routes for a specified period of time, even though routing
updates are not exchanged while the ISDN line is down. See the chapter
“Configuring DDR” in the Wide-Area Networking Configuration Guide for
detailed information about snapshot routing.