The MPLS WG Archive

[Nic Neate <Nic.Neate@dataconnection.com>]

Hi all,

I've not had any further discussion on this for a while.  This is a summary
of what I'm suggesting, taking into account the points people have made, and
what we've already resolved.  Please get back to me with any disagreement or
new arguments.

Thanks,

Nic


Agreed corrections to the draft
===============================

1.  Reflect in the description of the mplsFrrConstHopLimit field that the
information is not available at transit detour nodes.  Suggested text:

      DESCRIPTION
        "The maximum number of hops that the detour LSP may traverse.
         This field is not relevant and should be ignored if this 
         entry in the mplsFrrConstTable is being used in the context
         of representing a detour LSP."

2.  Typo: change mplsFrrConstExclAllAffinity to mplsFrrConstExclAnyAffinity.

3.  In section 5.3, change "mplsFrrDetourXCPointer" to
"mplsTunnelXCPointer".  In the DESCRIPTION of mplsFrrDetourActive, change
"mplsFrrDetourRole" to "mplsTunnelRole".

Outstanding suggested changes
=============================

1.  The mplsFrrConstTable should be a common table for both facility and
detour backup.  Currently it is defined to show "detour setup constraints".
However, the fields map precisely to those in the RSVP FAST_REROUTE object
and the FRR draft specifies that the FAST_REROUTE object applies equally to
both facility and detour backup.  Thus the table is required equally for
facilty and detour backup.

2.  The mplsFrrConstProtectionMethod should be a field in the
mplsFrrConstTable, not a scalar.  The FRR draft allows an LSR to
simulateously support LSPs using both facility and detour backup.  This is
likely to happen in real world networks, in particular when a network is
being migrated from one protection type to another.  Hence the protection
method needs to be configurable/reportable per-LSP, not just per-LSR.  I
suggest the follow text for the MIB.

   mplsFrrConstProtectionMethod OBJECT-TYPE
      SYNTAX        INTEGER { oneToOneBackup(0),
                              facilityBackup(1)
                            }
      MAX-ACCESS    read-write
      STATUS        current
      DESCRIPTION
        "Indicates which protection method is to be used for fast
         reroute."
      ::= { mplsFrrConstEntry 4 }

3.  The indexing of the mplsFrrConstTable needs fixing.  The current three
indicies (interface index, tunnel index and tunnel instance) are
insufficient.  For example, two protected LSPs could meet at a transit node,
both with different ingress and egress but the same values for each of the
existing mplsFrrConstTable indices.  If those protected LSPs have a
different value for, say, the mplsFrrConstSetupPrio then they need different
entries in the mplsFrrConstTable.

Rather than adjusting the current indexing, I suggest replacing the three
existing indices with a single integer index, mplsFrrConstIndex.  This index
can then be referenced from the mplsTunnelTable, establishing a simple
indexing system with clear relationships between the tables (which is also
in line with existing relationships between tables in the TE-MIB and
LSR-MIB).

Briefly, this would require the following.
- New mplsFrrConstIndex field in the mplsFrrConstTable, replacing the three
existing indices.
- New mplsFrrTunnelFrrConstIndex/Pointer field in the mplsTunnelTable,
pointing to the mplsFrrConstTable entry for this tunnel.

Some full suggested text follows.

For the mplsFrrConstTable:

   MplsFrrConstIndex ::= TEXTUAL-CONVENTION
      STATUS        current
      DESCRIPTION
        "Index into mplsFrrConstTable."
      SYNTAX  Integer32 (1..65535)

   mplsFrrConstIndex OBJECT-TYPE
      SYNTAX        MplsFrrConstIndex
      MAX-ACCESS    not-accessible
      STATUS        current
      DESCRIPTION
           "Uniquely identifies this row."
      ::= { mplsFrrConstEntry 1 }

For the mplsTunnelTable:

   -- MPLS Fast Reroute Tunnel Table

   mplsFrrTunnelTable            OBJECT-TYPE
      SYNTAX                     SEQUENCE OF MplsFrrTunnelEntry
      MAX-ACCESS                 not-accessible
      STATUS                     current
      DESCRIPTION
         "This table extends the mplsTunnelTable defined in the
          MPLS-TE MIB to provide Fast Reroute configuration."
      ::= { mplsFrrGeneralObjects 1 }

   mplsFrrTunnelEntry            OBJECT-TYPE
      SYNTAX                     MplsFrrTunnelEntry
      MAX-ACCESS                 not-accessible
      STATUS                     current
      DESCRIPTION
         "This entry provides Fast Reroute configuration for the
          tunnel."
      AUGMENTS { mplsTunnelEntry }
      ::= {mplsFrrTunnelTable 1}

   MplsFrrTunnelEntry ::= SEQUENCE {
      mplsFrrTunnelFrrConstPointer      RowPointer
   }

   mplsFrrTunnelFrrConstPointer   OBJECT-TYPE
      SYNTAX                      RowPointer
      MAX-ACCESS                  read-create
      STATUS                      current
      DESCRIPTION
           "This variable represents a pointer to the Fast Reroute 
             parameter specification for this tunnel.  This value may 
             point at an entry in the mplsFrrConstTable to indicate 
             which mplsFrrConstEntry is to be assigned to this LSP 
             instance.  This value may optionally point at an 
             externally defined Fast Reroute parameter specification 
             table.  A value of zeroDotZero indicates default Fast 
             Reroute parameters if the fastReroute bit in the 
             mplsTunnelSessionAttributes is set, and otherwise no Fast 
             Reroute protection."
      DEFVAL        { zeroDotZero }
      ::= { mplsFrrTunnelEntry 1 }

   END