Recently my company upgraded IOS on several hundred Cisco 2651XMs from 12.2.37 to 12.3.22a and we started having problems with some 50+ sites still on ISDN BRI as backup. We use dialer interface as multilink PPP logical interface. So on actual BRIs only thing configured is spids, dialer group and priority. On primary serial interface we use "backup interface dialer 0" command so when primary link goes down dialer kicks in. The problem is that when dialer kicks in only 1 B-channel stays up regardsless number of BRIs we're subscribed to. So for example if there is a site with 384k ISDN or 3 BRIs that would 6 B-channels and only one B-channel would stay up. I tried different parameters under 12.3.22a such as disabling TWAIT, chaning dialer load-thereshold, changing ppp multilink parameters with no avail. As soon as I revert that router back to 12.2.37 and perform a backup test all B-channels starts working fine. So far I tested at 8 different sites, I have Cisco TAC case open and working with an engineer and we are trying to identify a site that we can give it to Cisco Engineer for live test but before that I figured I ask you guys... I even verified the authentication on TACACS server and dialer authenticates correctly. here is a configuration....
interface Serial0/0
bandwidth 1536
backup delay 10 1
backup interface Dialer0
ip address 192.168.1.124 255.255.255.252
ip route-cache flow
max-reserved-bandwidth 100
service-policy output AMICOSA
!
... ... ...
!
interface BRI1/0
no ip address
encapsulation ppp
dialer rotary-group 0
dialer priority 4
dialer-group 1
isdn switch-type basic-ni
isdn spid1 94837648170101
isdn spid2 94837648230101
no cdp enable
!
interface BRI1/1
no ip address
encapsulation ppp
dialer rotary-group 0
dialer priority 3
dialer-group 1
isdn switch-type basic-ni
isdn spid1 94833745191101
isdn spid2 94833745118101
no cdp enable
!
!
interface Dialer0
ip address 172.16.18.124 255.0.0.0
encapsulation ppp
ip ospf network point-to-multipoint
ip ospf hello-interval 10
dialer in-band
dialer string 1888#######
dialer load-threshold 1 outbound
dialer-group 1
no cdp enable
ppp authentication chap
ppp chap password 7 ******************
ppp multilink
ppp timeout multilink link add 1
