The configuration for Legacy DDR requires a route to point packets out a particular physical interface. As
soon as the packets are routed out the interface, DDR logic can decide if the packet is interesting. If it is
interesting, DDR logic causes the dial to occur.
With Legacy DDR, there is no way to support a single set of remote sites through configuration using
multiple different BRIs or PRIs in a single router. When you have multiple BRIs or PRIs, Legacy DDR
allows you to dial only one set of sites using one interface and another set of sites with the other. In other
words, with Legacy DDR, the static routes used by DDR can direct packets out a single physical BRI
interface so that only a single BRI can be used to reach an individual remote site. Dialer profiles overcome
this problem with Legacy DDR using a slightly different style of DDR configuration. Dialer profiles pool
the physical interfaces so that the router simply uses an available B channel on any of the BRIs or PRIs in
the pool.
DDR dialer profiles are a different style of configuration for DDR. This style of configuration moves most
of the DDR interface configuration to a virtual interface called a dialer interface. Each physical BRI or PRI
interface can be included in a pool of available physical ISDN interfaces. DDR logic relies on the routing of
packets out the dialer interface. If a packet is interesting, DDR picks an interface from the pool over which
to place the actual call. The configuration for dialer profiles is very similar to Legacy DDR configuration:
The ip route command is again used to add IP routes to the router so that packets can be directed out the
BRI. Similarly, the access-list command defines the interesting logic and the dialer-list command
refers to those ACLs to define what is interesting and what is not.
The new commands: the interface dialer and dialer pool command creates the virtual dialer
interface and tells the router to look for any ISDN interface in the specified dialer pool to actually place the
call.