CCNA Cisco Certified Network Associate Study Guide - FTP Server

Dial-on-Demand Routing (DDR) 511
The second part of the SPID configuration is the local dial number for that
SPID. It is optional, but some switches need to have those set on the router
in order to use both B channels simultaneously.
An example is shown below:
RouterA#config t
Enter configuration commands, one per line. End with CNTL/Z.
RouterA(config)#isdn switch-type basic-ne1
RouterA(config)#int bri0
RouterA(config-if)#encap ppp (optional)
RouterA(config-if)#isdn spid1 086506610100 8650661
RouterA(config-if)#isdn spid2 086506620100 8650662
The isdn switch-type command can be configured in either global configuration
or interface configuration mode. Configuring the switch type global will
set the switch type for all BRI interfaces in the router. If you only have one
interface, it doesn’t matter where you use the isdn switch-type command.
Dial-on-Demand Routing (DDR)
Dial-on-demand routing (DDR) is used to allow two or more Cisco
routers to dial an ISDN dial-up connection on an as-needed basis. DDR is
only used for low-volume, periodic network connections using either a Public
Switched Telephone Network (PSTN) or ISDN. This was designed to
reduce WAN costs if you have to pay on a per-minute or per-packet basis.
DDR works when a packet received on an interface meets the requirements
of an access list defined by an administrator, which defines interesting
traffic. The following five steps give a basic description of how DDR works
when an interesting packet is received in a router interface:
1. Route to the destination network is determined.
2. Interesting packets dictate a DDR call.
3. Dialer information is looked up.
4. Traffic is transmitted.