When a dialer interface? say, ISDN? comes up, it could be desirable to run a routing protocol over this link. Static routes might do the job, but in networks with a large number of routes, static routes might not scale well. Therefore, running a dynamic routing protocol is necessary. In some situations, the ISDN link is up but no routing information is going across. Without a routing protocol, no destination addresses can be learned and no traffic can be sent to those destinations. This problem needs to be fixed because ISDN interfaces are of no use when not carrying any traffic.
Figure 5-36 shows the flowchart to follow to solve this problem.
Figure 5-36. Problem-Resolution Flowchart
IGRP updates are not going across the dialer interlace.
IGRP uses a broadcast for routing updates. When using IGRP over ISDN implementations* t>e certain to include llie broadcast keyword in dialer map statements. Go to Debug* and Verification section.
Example 5-90 shows the configuration on R1 that produces this problem. The dialer map is used to map the neighbor IP address with a string, which is normally an ISDN number. This is called a static mapping for dialer. When using static mapping, the keyword broadcast must be included at the end; otherwise, it will not propagate the broadcast traffic across the link.
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