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Applying the Dial-on-Demand Dialer Filter to the Dialer Interfaces

Dial-on-demand routing (DDR) links two sites over a public network and provides bandwidth. An ISDN connection allows an ISDN line to be activated only when there is network traffic configured as an “interesting” packet. An interesting packet is defined using the firewall filter feature of the Services Router.

To configure DDR, you configure the dialer interface as a passive static route with a lower priority than dynamic routes. If the dynamic route is lost, and a packet destined for that IP address is received, the dialer interface initiates an ISDN connection and sends the packet over it. When no new packets are sent to the destination, the dialer interface initiates an inactivity timer. The ISDN connection is terminated when the timer expires.

There are three steps to configuring dial-on-demand connectivity:

Define the dialer filter.
Configure the firewall rule.
Apply the dialer filter to the dialer interface.

To define the filter, include the dialer-filter interesting-traffic statement at the [edit firewall family inet] hierarchy level.

To configure the firewall rule, include the term and from statements at the [edit firewall family inet dialer-filter filter-name] hierarchy level.

To apply the filter to the dialer interface, include the filter dialer statement at the [edit interfaces dln unit logical-unit-number family family] hierarchy level.

Example: Applying the Dialer Filter

The following example illustrates a dialer filter configuration configured at the [edit firewall family inet] hierarchy level and applied to a physical interface and a dialer interface.

See Figure 52 for the topology used for this example.

Figure 52: Dialer Filter Topology

Image g017022.gif

Configuration for the Dialer Filter



edit firewall familyinet
dialer-filter interesting-traffic {


term 1 {


from {


destination-address {
100.0.0.50/32;
}


}


then note;
}


}

Configuration on the Dialer Interface



[edit interfaces]
dl0 {
encapsulation ppp;


unit 0 {


dialer-options {
pool 1;
dial-string 350100;
}


}




family inet {


filter {
dialer interesting-traffic;
}


address 50.2.0.1/24;
}


}

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