Subject: L2TP MIB support for PPP over ATM

From: "Ettore Guadagnino" <[email-masked]>
Date: Tue, 13 Jun 2000 12:52:08 +0200

Hi all,

we have a question about use of the Session Map Table as defined
in the  L2TP-MIB (<draft-ietf-l2tpext-l2tp-mib-00.txt>) and would
appreciate any clarification from you.

Paragraph 3.4 of the document states:

"...l2tpSessionMapTable table provides management
 applications to determine which session within a
 tunnel a particular interface  (either a PPP or DS0
 interface) is mapped to. On the LAC it also provides
 a management application the ability to map a particular
 physical or virtual interface terminating a PPP link
 to a particular L2TP tunnel. This is required since the
 interface stacking as performed (and instrumented by
 the ifStackTable) on the LNS cannot be applied at the LAC.
"

When the subscriber is connected via PPP over ATM,  the interface terminating
the PPP link on a LAC should be of type AAL5.
As AAL5 supports multiplexing of VC connections, a single AAL5 interface
could terminate many VCCs from one or more subscribers.  In this context a
PPP session is associated to a VCC on an AAL5 interface and thus is uniquely
identified by the triplet  <aal5IfIndex, Vpi, Vci>

The l2tpSessionMapTable as defined into the MIB does not allow to associate
the PPP  session inside a tunnel to a VCC.  A similar problem seems to be
present also for the l2tpSessionStatsTable.

Does this mean we need to define one virtual interface for each VCC
carrying PPP packets?  This would imply an heavy overhead to fully support
all mandatory ifTable objects and ifStackTable bindings, althought not stricly
neeeded.

The same considerations seems apply also to PPPoE.
What is your opinion about this point?

Thank you in advance,
Ettore & Giovanni

===================================================================
Ettore Guadagnino
Marconi Communications
E-mail: [email-masked]
tel: +39 10 6003622
===================================================================
Giovanni Vitiello
Getronics
E-mail: [email-masked]
tel: +39 125 521261
===================================================================

---

From: Evan Caves <[email-masked]>
Date: Tue, 13 Jun 2000 18:09:53 -0700

Ettore Guadagnino wrote:
> carrying PPP packets?  

Yes.

> This would imply an heavy overhead to fully support

If you were not tunneling PPP you would have to bind the <al5IfIndex,
Vpi, Vci>
to a virtual port anyways otherwise you could not manage the PPP
interface.

evan
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