Example 9-245 shows the configuration on R1 that can produce this problem. In this configuration, only TCP traffic is denied. In other words, TCP traffic will not bring up the link, but any other IP traffic can do so.
Example 9-245 R1's Access List Denies Only TCP Traffic
ip address 192.168.254.13 255.255.255.252 encapsulation ppp dialer map ip 192.168.254.14 name R2 broadcast 57654
dialer-group 1 page 283
isdn switch-type basic-net3
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The OSPF demand circuit feature was introduced in Cisco IOS Software Release 11.2. This feature forms the OSPF adjacency over a link and then later keeps the Layer 2 down to save the toll charges while keeping the OSPF adjacency over this link. If the link keeps coming up, it defeats the purpose of a demand circuit.
The most common possible causes of this problem are as follows:
• A link flap exists in the network.
• The network type is defined as broadcast.
• A PPP host route is getting redistributed into the OSPF database.
• One of the routers is not capable of using a demand circuit.
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