Ok, here are the parts of my config:
card type e1 0 0
!
isdn switch-type primary-net5
!
voice-card 0
no dspfarm
dsp services dspfarm
!
username XXX password XXX
!
controller E1 0/0/0
pri-group timeslots 1-31
description *** Voice ***
!
controller E1 0/0/1
pri-group timeslots 1-31
description *** ISDN-Backup ***
!
interface Serial0/0/0:15
no ip address
encapsulation hdlc
isdn switch-type primary-net5
isdn incoming-voice voice
no cdp enable
!
interface Serial0/0/1:15
description *** ISDN-Backup Arcor ***
no ip address
encapsulation hdlc
dialer pool-member 2
no snmp trap link-status
isdn switch-type primary-net5
isdn answer1 xxxxxxx
isdn calling-number xxxxxxx
isdn sending-complete
!
interface Dialer100
description *** ISDN-Backup ***
ip address 10.x.xxx.xx 255.255.255.254
encapsulation ppp
ip summary-address eigrp 597 10.x.xxx.xx 255.255.252.0
ip summary-address eigrp 597 10.x.xxx.xx 255.255.252.0
dialer pool 2
dialer remote-name xxxxx
dialer string xxxxxxxxxxxxxx
dialer hold-queue 5
dialer load-threshold 40 either
dialer-group 1
no snmp trap link-status
ppp authentication chap
voice-port 0/0/0:15
!
voice-port 0/0/1:15
Port 0/0/0 is configured for voice, and 0/0/1 should be configured for isdn backup.
