4000 Router Series Layer 2 - WAN Configuration Guide

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Configuration example for circular dial string backup and

Internet access with DDR

Network requirements

As shown in Figure 47:

• Router B operates as an access server and is configured with an IP address of 100.1.1.254/24. It

uses the address range of 100.1.1.1/24 to 100.1.1.16/24 for address assignment. The PSTN dial

strings available on it are 8810048 through 8810055, allowing the router to provide services to 16

online users.

• Router A accepts the IP address assigned by Router B.

Configure Router A on the dialup side to implement cyclic dial string backup with dialer routes. Configure

Router B on the access side to use asynchronous serial interfaces to provide DDR dialup access and

adopt PAP to authenticate the dialup side.

As shown in Figure 48, th

e configurations of Router C and Router D are the same as those of Router A

and Router B, except that Router D uses an ISDN dial string 8810048 rather than PSTN dial strings to

provide services.

Configure Router C and Router D to implement DDR with one dial string and use CHAP for

authentication.

Figure 47 Network diagram for dial string backup/access service with DDR (PSTN mode)