WAN Backup over ISDN

[zirbo]

I found this sample config on CCO and have trouble understanding why interesting traffic is defined, since the backup interface command is used.

In my understanding, when the main link drops, the backup dialer interface (which has been kept in standby) goes up (the dialling occurs), then down - when the main link is back up, with consideration to

the timers configured in the backup delay command.

As I see for now - backup interface and defining interesting traffic + proper routing info are 2 separate ways of causing the backup interface to dial, and this configuration would work the same without the dialer-list + dialer-group parts

Sample config:

<deleted>

isdn switch-type basic-ni

!

interface Serial0

backup delay 10 30

backup interface Dialer1

ip address 192.168.10.2 255.255.255.252

encapsulation ppp

!

interface BRI0

no ip address

encapsulation ppp

dialer pool-member 10

isdn switch-type basic-ni

ppp multilink

!

interface Dialer1

ip address 172.20.10.2 255.255.255.0

encapsulation ppp

dialer pool 10

dialer idle-timeout 900

dialer string 5552222

dialer load-threshold 80 outbound

dialer-group 1

ppp multilink

!

dialer-list 1 protocol ip permit

<deleted>

Link to the full document:

http://cisco.com/en/US/tech/tk801/tk379/technologies_configuration_example09186a008010456b.shtml

-------

It's me again and I have found the explanation:

it seems that for the 3 dial-backup methods - backup interface, floating static routes and dialer-watch, in order for the call to be placed, the first 2 need the interesting traffic to be defined and the 3rd does not.

[Georg Pauwen]

Hello,

wether the ISDN is used as a backup or not, the dialer-list and the dialer-group commands are always required, otherwise the ISDN will not work.

Not sure if this answers your question - if you have access to an ISDN line, try to configure the BRI (or a dialer) without those two statments, and you will see that it doesn't work.

Regards,

GP