ISDN backup for MPLS link with loadbalncing

Unanswered Question
Dec 4th, 2008

I want to configure ISDN link as backup of my MPLS link with loadbalancing .Senerio is like this if my MPLS link utilization will exceded then 80% of MPLS link capacity , some traffice will auto matically diverted through ISDN.

Any one help me.

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Overall Rating: 4 (1 ratings)
Giuseppe Larosa Thu, 12/04/2008 - 00:53

Hello Sujeet,

ISDN access to an MPLS VPN is possible using a feature called dialer map VRF aware:

the PE ISDN is able to answer calls from CE not to call.

on receiving the call the PE can associate the call with the right VRF.

Some attributes can be stored on the Radius server and downloaded during ppp authentication of the CE router


I tested it some years ago and it worked

Hope to help


sujitkr7cisco Thu, 12/04/2008 - 01:59

Dear Giuseppe,

Thanks for reply,

Can we use ISDN link as a loadbalance link if my primary MPLS link utilization is over 80%. or can we use here ISDN as a load shareing link with MPLs primary link .



Giuseppe Larosa Thu, 12/04/2008 - 03:02

Hello Sujeet,

in my tests I used it only as backup in case of primary link failure.

Using it when MPLS link utilization is over 80% appears possible using the backup load command options

the isdn link is defined as the backup of the primary (they must be on the same CE router)

However, verify if you have a flat rate ISDN fee otherwise it is better to use it only for backup.

backup load

Hope to help


sujitkr7cisco Fri, 12/05/2008 - 01:37

Dear All,

Senerio is like this,

I got MPLS link and ISDN link both are from single ISP and these links are also terminated on one cisco 1800 router .Right now ISDN as a backup is working but loadsharing is not hsappening .

Thanks for reply .



Giuseppe Larosa Fri, 12/05/2008 - 14:02

Hello Sujeet,

if you like you can post part of your configuration of your 1800 router.

Just mask public ip addresses and removes passwords

To trigger the ISDN link you could try to use backup load 1

However, if ISDN is not flat rate using it as a backup only is the best choice.

traffic inbound is decided by service provider it is highly probable that the ISDN link is terminated on another PE router to provide node fault tolerance but the SP routing will prefer the path via the normal link because the service is thought for backup.

Hope to help



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