ISDN & authentication

[vinaymurthy]

Hi,

Is Authentication (PAP/CHAP) is a must in ISDN establishiment?

Regards

Vinay

[parvees123]

Hi Vinay,

Yeah what you said is correct, For ISDN establishment we should use the encapsulation method ... and we select PPP as the encapsulation to establish connection between different vendor devices. HDLC is used on ly for Cisco devices. So if we seldcted encapsulation as PPP , then we should use some authentication protocol which PPP support, and for that we use PAP/CHAP. Detail information is attached with this reply. I think it would be helpful for you...

If you find this information good enough rate it :-)

Regards,

PSM

[vinaymurthy]

Hi,

Thanks for the info provided.

I did see many of the configs requiring PAP or CHAP.

So, ISDN doesnot works if no authentication is mentioned or configured. is it so?

IS there any default authentication config for ISDN?

Regards

Vinay

[parvees123]

Dear Vinay,

Yes you are right, we ussually use authetication for security purpose. and it should be used in the configuration.

There is not defualt authentication for ISDN, but we normally use CHAP as it enrypt password.

Regards

PSM

[vinaymurthy]

Hi,

Thanks for the info on PPP CHAP/PAP.

IS ppp multilink command is a must if i am configuring the PPP authentication.

I have two routers connecting to central router. I can only assign maximum one channel to each router, as there is only one ISDN line. in that case, i dont have to configure PPP multilink right????

Regards,

Vinay

[Georg Pauwen]

Hello Vinay,

in addition to what PSM said, authentication is indeed not required for ISDN to work, but usually, the very reason PPP encapsulation is being used is that it supports authentication...

Regarding PPP multilink, it is not related to authentication. As you said, since you have two remote routers, PPP multilink is not a probably not a good option...

Regards,

GP

[vinaymurthy]

Hi GP,

Thanks for the inputs, I do not want to configre PPP authentication & still wouldlike to use PPP as encapsulation, is that possible?

To best of my knowledge PPP multilink will bundle both the channels. so if i have each channel dedicated to one remote router,Configuring PPP multilink will cause a problem?

[Richard Burts]

Yes it is technically possible to configure PPP encapsulation and not configure any authentication. If you configure this the interface will come up and will transmit data.

You may find that it does not work quite the way you expect if you do not configure authentication. In particular my experience has taught me that if I configure ISDN BRI between two routers (say RTA and RTB) and do not configure authentication something unexpected happens. If RTA pings RTB it will bring up the first B channel to send the ping. And when RTB sends the response it will bring up the second B channel. You can not use just a single channel if you do not authenticate. Part of the explanation of this is that without authentication RTB answers a call and receives the ping request. When RTB gets ready to send the ping response it is not aware that it already has a connection to RTA which it could use, and brings up a channel to send the response. If you do authenticate then the routers will communicate properly over a single channel.

For this (and some other reasons) it is usually best to configure authentication. But if you want to not configure authentication the ISDN should still work.

HTH

Rick

[vinaymurthy]

Hi,

what should be the dialer interface status, when it is configured as backup. IT shows be standby, down.

When i shutdown the serial interface to test the ISDN, the dialer interface goes to Standby/Disabled, down mode.

Can any one guide me on this

Regads

Vinay

[Richard Burts]

Vinay

When configured as backup interface the status of dialer interface should be standby, this is normal behavior. When configured as backup interface the dialer will not initiate a call and will not answer a call. Only in the case of a failure of the primary interface will the backup come out of standby status.

One interesting aspect of using backup interface is that shutting down the primary interface (serial) is that this does not constitute a failure. The IOS recognizes that you have shut down the interface and believes that you must have meant for it to go down and does not treat the event as a failure and the backup interface is still in standby mode. To test the backup you must produce a failure of the primary such as unplugging the cable.

HTH

Rick