Subject: FW: [L2tpext] FW: Service-Name TAG

From: Nurit Sprecher <[email-masked]>
Date: Thu, 27 Dec 2001 10:23:48 +0200

-----Original Message-----
From: Nurit Sprecher 
Sent: Thursday, December 27, 2001 09:55 
To: 'James Carlson'
Subject: RE: [L2tpext] FW: Service-Name TAG

Thanks for your reply.
Yes, I did mean PPPoE 'Service name' TAG.
I am interesting in service selection functionality in an environment of PPP
access over ADSL. The usual way to perform a service selection (at least as
ADSL forum defines) is to base it on the domain name appears in the PPP user
name (in the authentication string). I wonder if in case of PPPoE access
protocol I can base the decision on the service TAG appears  in the
discovery stage.

Please advice me.
Thanks in advance, Nurit.

-----Original Message-----
From: James Carlson [mailto:[email-masked]]
Sent: Wednesday, December 26, 2001 19:57
To: Nurit Sprecher
Cc: L2tp (E-mail)
Subject: Re: [L2tpext] FW: Service-Name TAG

> Can someone tell me what is the common attribute which is carried within
the
> service-name tag?

L2TP doesn't have a service name tag.  Are you perhaps thinking of
PPPoE?

> I understand that it may be the ISP name or the CoS. Can I
> expect that the service name tag will be identical to the qualified domain
> name that appears in the user name in the PPP authentication phase?

For PPPoE, no.  The contents of the RFC 2516 "Service-Name TAG" is an
arbitrary string assigned by the administrator of the PPPoE server.

Out of curiosity, I have to ask: if you were to expect that it had any
relation to PPP authentication, how would your system behave any
differently?  In other words, what did you plan to do with the
Service-Name TAG contents?

--
James Carlson                                  <[email-masked]>

---

From: James Carlson <[email-masked]>
Date: Thu, 27 Dec 2001 08:46:28 -0500 (EST)

Nurit Sprecher writes:
> name (in the authentication string).

That doesn't quite make sense to me.  The Service-Name TAG appears
before the session is established and thus well before any PPP packets
are sent -- including PPP authentication.  In addition, PPPoE has no
authentication at all.

I've seen a wide variety of uses of the Service-Name TAG.  Some ISPs
leave it blank or omit it entirely.  Some include a domain name.  Some
include the tag multiple times and list several different domains.

If it has a relationship with the PPP authentication services, it's
certainly not obvious to me, nor is it defined anywhere in the
protocol documents.

Moreover, as I asked before, what would you do differently if it
*were* the same as the peer name given during PPP authentication?  How
does that help or hurt your implementation?

> I wonder if in case of PPPoE access

"The decision?"  What decision?

You can use it in any way that you might use an unauthenticated
attribute, similar to a telephone number received by Caller*ID or ANI.

In my implementation (Solaris PPP 4.0), I do the following:

	- I allow the server side to offer multiple service names and
          (internally) associate a PPP configuration with each.

	- When a client requests a particular service, I select that
          configuration when building the session.

	- If a client specifies the wildcard (blank) service, then I
          just pick the first one on the list.

	- In the client side, I allow the user to omit the service
          (the default), and I ask the server for a wildcard service.
          Otherwise, if the user gives a particular name, then I
          ignore all other offered services and refuse to establish a
          session unless (and until) I see the one specified.

I think what you do with service names is entirely up to you.  I don't
see how (or why) this treatment would be specified as a requirement
for an implementation.

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