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Multiple ISPs & single IP/MPLS/ADSL infrastructure

Actually very soon we'll have an IP/MPLS core network with ADSL access network.

What we are going to do is to make several ISPs to use the IP/MPLS core in order to provide internet to their users.

Can we configure an MPLS VPN for each Service Provider so that it can support the ADSL users from its own Backbone. (I suppose that the MPLS VPN will span several cities, and it will be secure and totally separate from other ISPs MPLS VPNs) .

If so , can an ASDL user choose the ISP that he wants , or the ADSL port will be dedicated for a specific ISP.

Could you provide me with examples for multiple ISPs that use the same IP/MPLS/ADSL infrastructure & what are the all existing(already applied in the real world) senarios ?

Thank You in advance


Re: Multiple ISPs & single IP/MPLS/ADSL infrastructure

There is something called Carrier supporting Carrier where a service provider allows another service provider to use its backbone network The backbone service provider treats each service provider as a separate MPLS VPN customer who in turn can offer MPLS VPN service to their end customers. Check this link for more information :

Community Member

Re: Multiple ISPs & single IP/MPLS/ADSL infrastructure

NO, The ADSL User cannot choose the ISP of his choice. He will have to connect using the ISP from which he has taken the ADSL connection (Physical Connection from the ISP-DSLAM). Again it depends on the Understanding og the ISP's to allow users to roam using each others connection.

As rightly pointed each ISP using your MPLS backbone will be treated as separate VRF entities. and if the ISP's decide to give the flexibility to its user to choose any other ISP apart from itself then at the device acting as PE to the ISP1 and ISP2, configure a new VRF if the user wants to use the same adsl connection to access using a ISP other than the one from whome he has taken the ADSL port.

See the attached file for more details.

and also check out the below URL for more details on MPLS/IP/DSL

Community Member

Re: Multiple ISPs & single IP/MPLS/ADSL infrastructure


You can definitly do what you described. actually i am a network engineer for an isp that uses exactly that service from a carrier. there are at least 10 more isps on that share this mpls core to reach that carriers dsl customers.

There are few ways i know to do while enabling users to select their isp:

use PPPoE or PPPoA for the dsl users. get those dsl users to terminate at your BRAS (which should also be a PE in some of the options (for example a7301 routers stack). from this point the solution divides to two options:

1. this option is faster but not so acaleable.

In this option you termintae the ppp sessions sends a radius request to your radius server that by the domain name recognizes to which isp the customer belongs to (for example vs, and forward the request to that isp radius which then authorizes it and within the response sends an vrf selection. then the users belongs to that vrf on your network that belong to that isp.

in this option one dsl user can have severel isp accounts and switch between them by changing the credientials in his ppp software.

2. this options requires a more comples system from the isp but gives him much greater control over his subscribers and saves you a hell of a management burden. this options begin like the previous one with a PPPoE/PPPoA session coming from the dsl users to your BRAS (which doesn't need to be a PE but rather be a CE) however this time the BRAS is configured not the teminate the ppp sessions but to map them (by the domain name) to l2tp tunnels which will terminate in the isp BRAS. in this scenario all isps can share the same vrf since they get the l2tp/ppp seperation of each user session.

It gives he isp many advantages like controlling the addressing, applying serivces etc etc. again users can switch between isps by changing the username@doamin at their ppp software.

The third option is based on service selection devices like cisco ssg. in this option you can use the adsl in 1483b mode (cisco rbe for example).the service selection device is the one that terminates the atm pvcs from the dslam. when the users is trying to access the internet he is presented with captive web page where he is required to authenticate with his isp. this authentication request is then proxied to the right isp (again by the domain) which replys with a radius response that include the vrf assignment. again users can switch between isps any time.

I hope this helps.

If you require further clarifications you are welcome to contact me at:


Amos Rosenboim

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