CCNA ISDN Legacy, Profiles, DDR etc.

[jabw]

Hi,
I'm studying for CCNA 640-801.

I'm having problems understanding the different concepts used for configuring ISDN.
I read about Legacy DDR and about Dialer Profiles and DDR.
It looks as if they are different but also bits of it looks the same? It's very confusing.
Could do with a good explanation on this issue.

 

[Cluebird]

Dial on Demand Routing (DDR) can be implemented with legacy dialup or dialer profiles. Legacy dialup and dialer profiles are both used over demand circuits to route traffic and both methods work well. Dialer profiles just make the configuration modular so you don't have to lock a physical interface into one configuration.

In a configuration, legacy dialup uses a "dialer map..." command under a physical interface while dialer profiles use a "dialer string..." command under a logical (dialer) interface.

The terminology is what causes the confusion to most people since the actual configuration for most scenarios boils down to: 1. Create a static route, 2. Define interesting traffic, 3.Define the Layer3 to Layer 2 address resolution with a dialer map or within a dialer profile. After that we usually add ppp encapsulation so we can to CHAP and multilink and then tweak some timers.