query on draft-ietf-iplpdn-frmib-dte-04.txt

John Shriver <jas@shiva.com> Tue, 09 May 1995 19:41 UTC

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From: John Shriver <jas@shiva.com>
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To: cbrown@wellfleet.com, charles@acc.com, fred@cisco.com
CC: iplpdn@CNRI.Reston.VA.US
Subject: query on draft-ietf-iplpdn-frmib-dte-04.txt

How does one uses this draft MIB (or RFC 1315) to express things like:

1. Novell's model of each Frame Relay DLCI is one IPX network.

2. Cisco's implementation of "subinterfaces" on a Frame Relay
interface, allowing multiple IP nets for various aggregations of
DLCI's.

It looks like the MIB evolved in the old model of "one Frame Relay
interface :== one network layer interface :== one SNMP interface".

The description of:

    frCircuitIfIndex OBJECT-TYPE
        SYNTAX   Index
        MAX-ACCESS   read-only
        STATUS   current
        DESCRIPTION
           "The ifIndex Value of the ifEntry this  virtual
           circuit is layered onto."
       ::= { frCircuitEntry 1 }

only binds it to the underlying FR interface.  It doesn't provide that
this entry may be all (or part of) an SNMP interface as seen by the
network protocols.

In either of these, the most "RFC 1573 way" would seem to be to have
one SNMP "interface" for each of these DLCI's or DLCI clusters.  (Somewhat
like the way PPP runs over RS-232.  Yeah, I don't enjoy that either.)

Although, RFC 1573 admits:

   Several of the sub-layers for which media-specific MIB modules have
   been defined are connection oriented (e.g., Frame Relay, X.25).
   Experience has shown that each effort to define such a MIB module
   revisits the question of whether separate conceptual rows in the
   ifTable are needed for each virtual circuit.  Most, if not all, of
   these efforts to date have decided to have all virtual circuits
   reference a single conceptual row in the ifTable.

On the other hand, RFC 1573 says:

3.2.4.  Virtual Circuits

   This memo strongly recommends that connection-oriented sub-layers do
   not have a conceptual row in the ifTable for each virtual circuit.
   This avoids the proliferation of conceptual rows, especially those
   which have considerable redundant information.  (Note, as a
   comparison, that connection-less sub-layers do not have conceptual
   rows for each remote address.)  There may, however, be circumstances
   under which it is appropriate for a virtual circuit of a connection-
   oriented sub-layer to have its own conceptual row in the ifTable; an
   example of this might be PPP over an X.25 virtual circuit.  The MIB
   in section 6 of this memo supports such circumstances.

   If a media-specific MIB wishes to assign an entry in the ifTable to
   each virtual circuit, the MIB designer must present the rationale for
   this decision in the media-specific MIB's specification.


I'm opening a can of worms, aren't I?  (Or did Novell open it first?)
Even RFC 1490 doesn't really talk about this issue.  I did look at
back archives of the list first.  Nothing there on this issue in
1994-95.