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New Member

ISDN ISP Dial Access from C876

I have a Cisco 876W router and would like some assistance to enable the router to connect to ISP using the ISDN interface as the WAN link. The IOS has been upgraded to c870-advipservicesk9-mz.124-15.T7.bin. I have attached the running-config file The link led light on the router front panel is lit and the cd light is also blinking. The BRI0 & Dialer0 config were obtained from website. Please know that I am relatively new to cisco routers. I have tried different ISDN cables between telco ISDN unit and the router (all to no avail). Is a chat script required to initialize the ISDN dial up system in a way analagous to modem chat script initialization? SDM Config helped set up basic router configuration. Do I need to contact ISP for advice from their side?

Hall of Fame Super Silver

Re: ISDN ISP Dial Access from C876

Hello Philip,

you need to contact ISP people for sure to know what account to use and what authentication protocol, and how they present to you

Under int dialer config you need:

ppp authentication pap chap

in global config you need

username isp-remote-name password shared-pwd

or other variations like:

ppp authentication pap chap callin

you can troubleshoot using

terminal monitor

debug ppp negotiation

debug ppp authentication

if you like you can attach in a text file the output of the show commands

But the first step is to contact your ISP.

to check isdn use

sh isdn status

it should show

L1: activated

L2 multiple-frame-established

Hope to help


New Member

Re: ISDN ISP Dial Access from C876

Many thanks Giuseppe for bothering to reply:

I don't know if the following is any help. I haven't got any output from the debug settings.

The output of show isdn status is as follows:

Global ISDN Switchtype = basic-net3

ISDN BRI0 interface

dsl 0, interface ISDN Switchtype = basic-net3

Layer 1 Status:


Layer 2 Status:


Layer 3 Status:

0 Active Layer 3 Call(s)

Active dsl 0 CCBs = 0

The Free Channel Mask: 0x80000003

Total Allocated ISDN CCBs = 0

I have the correct ISP login details entered into the running-config file. I can authenticate to ISP under Linux with an ISDN T/A using /etc/ppp/pap or chap-secrets. I masked out ISP Login details in the config file posted earlier.

Hall of Fame Super Silver

Re: ISDN ISP Dial Access from C876

Hello Philip,

the best way is to do

int bri0


then you do

terminal monitor

debug ppp neg

debug ppp auth

int bri0

no shut

this triggers a new negotiation

ISDN status is fine

to use authentication you need


ppp authentication pap chap

command under dialer interface

Hope to help


Hall of Fame Super Gold

Re: ISDN ISP Dial Access from C876

According to the datasheet:

you need advanced enterprise image for ISDN primary WAN link. Other images can only use the BRI port for out-of-band management.