NAS, LNS, PPP, L2TP need help here!

[rcasta]

Hello,

Listen, following the above scenario, please point me out into the right direction:

* Have a host who doesn't talk L2TP dials up (56kbps modem) and initiates a PPP session to a NAS, then gets authenticated by a radius server.
* Radius server sends the NAS the authorization. * * Thereafter the NAS sets up an L2TP tunnel towards an LNS.
* The LNS bypasses ppp authentication (no need for doing
this at least under this scenario for it's been already
authenticated by the NAS/Radius the first time).
* The LNS then grants the host with an ip address.

Question: The L2TP tunnel begins at the NAS and ends in the LNS. But what about the PPP session? It clearly starts from the host, but where does it end? in the NAS or in the LNS???? Explanation?

Best regards,

 

[orb1tals]

The PPP session starts at the host and ends at the NAS. PPP is point to point and the client will negotiate link and authentication parameters with the NAS.
The fact that you are tunnelling (L2TP) suggests that there must be another administrative domain (perhaps a reseller) that client is subscibing to.
The initial authentication verifies that this user is allowed to dialup this NAS and I am pretty sure that the user is authenticated again at the LNS to verify that the user is a subscriber, at which point an IP address is allocated. If you look at he user connection on the NAS you would probably see him/her issued with a 0.0.0.0 ip address because this is not the service termination point. As I do not more information on the scenario, I cannot be alsolutely sure.

Dean

 

[orb1tals]

P.S
Perhaps L2TP is being used to tunnel other protocols within the same administrative domain.

 

[orb1tals]

PPS
The NAS may extend the PPP session to the LNS which will then terminate the session.

 

[rcasta]

Thank you all for giving a clear, nicely explained replies.

best regards,