Subject: [mpls] [Editorial Errata Reported] RFC3811 (1882)

From: RFC Errata System <[email-masked]>
Date: Wed, 16 Sep 2009 11:04:14 -0700 (PDT)

The following errata report has been submitted for RFC3811,
"Definitions of Textual Conventions (TCs) for Multiprotocol Label Switching (MPLS) Management".

--------------------------------------
You may review the report below and at:
http://www.rfc-editor.org/errata_search.php?rfc=3811&eid=1882

--------------------------------------
Type: Editorial
Reported by: Vishwas Manral <[email-masked]>

Section: MplsLabel

Original Text
-------------
       MplsLabel ::= TEXTUAL-CONVENTION
          STATUS        current
          DESCRIPTION
             "This value represents an MPLS label as defined in
              [RFC3031],  [RFC3032], [RFC3034], [RFC3035] and
              [RFC3471].

              The label contents are specific to the label being
              represented, such as:

              * The label carried in an MPLS shim header
                (for LDP this is the Generic Label) is a 20-bit
                number represented by 4 octets.  Bits 0-19 contain
                a label or a reserved label value.  Bits 20-31
                MUST be zero.

                The following is quoted directly from [RFC3032].
                There are several reserved label values:

                   i. A value of 0 represents the
                      'IPv4 Explicit NULL Label'.  This label
                      value is only legal at the bottom of the
                      label stack.  It indicates that the label
                      stack must be popped, and the forwarding
                      of the packet must then be based on the

Nadeau & Cucchiara          Standards Track                     [Page 5]

RFC 3811                      MPLS TC MIB                      June 2004

                      IPv4 header.

                  ii. A value of 1 represents the
                      'Router Alert Label'.  This label value is
                      legal anywhere in the label stack except at
                      the bottom.  When a received packet
                      contains this label value at the top of
                      the label stack, it is delivered to a
                      local software module for processing.
                      The actual forwarding of the packet
                      is determined by the label beneath it
                      in the stack.  However, if the packet is
                      forwarded further, the Router Alert Label
                      should be pushed back onto the label stack
                      before forwarding.  The use of this label
                      is analogous to the use of the
                      'Router Alert Option' in IP packets
                      [RFC2113].  Since this label
                      cannot occur at the bottom of the stack,
                      it is not associated with a
                      particular network layer protocol.

                 iii. A value of 2 represents the
                      'IPv6 Explicit NULL Label'.  This label
                      value is only legal at the bottom of the
                      label stack.  It indicates that the label
                      stack must be popped, and the forwarding
                      of the packet must then be based on the
                      IPv6 header.

                  iv. A value of 3 represents the
                      'Implicit NULL Label'.
                      This is a label that an LSR may assign and
                      distribute, but which never actually
                      appears in the encapsulation.  When an
                      LSR would otherwise replace the label
                      at the top of the stack with a new label,
                      but the new label is 'Implicit NULL',
                      the LSR will pop the stack instead of
                      doing the replacement.  Although
                      this value may never appear in the
                      encapsulation, it needs to be specified in
                      the Label Distribution Protocol, so a value
                      is reserved.

                   v. Values 4-15 are reserved.

              * The frame relay label can be either 10-bits or
                23-bits depending on the DLCI field size and the
                upper 22-bits or upper 9-bits must be zero,
                respectively.

              * For an ATM label the lower 16-bits represents the
                VCI, the next 12-bits represents the VPI and the
                remaining bits MUST be zero.

              * The Generalized-MPLS (GMPLS) label contains a
                value greater than 2^24-1 and used in GMPLS
                as defined in [RFC3471]."
          REFERENCE
             "Multiprotocol Label Switching Architecture,
              RFC3031.

              MPLS Label Stack Encoding, [RFC3032].

              Use of Label Switching on Frame Relay Networks,
              RFC3034.

              MPLS using LDP and ATM VC Switching, RFC3035.
              Generalized Multiprotocol Label Switching
              (GMPLS) Architecture, [RFC3471]."
          SYNTAX  Unsigned32 (0..4294967295)

Corrected Text
--------------
       MplsLabel ::= TEXTUAL-CONVENTION
          STATUS        current
          DESCRIPTION
             "This value represents an MPLS label as defined in
              [RFC3031],  [RFC3032], [RFC3034] and [RFC3035].

              The label contents are specific to the label being
              represented, such as:

              * The label carried in an MPLS shim header
                (for LDP this is the Generic Label) is a 20-bit
                number represented by 4 octets.  Bits 0-19 contain
                a label or a reserved label value.  Bits 20-31
                MUST be zero.

                The following is quoted directly from [RFC3032].
                There are several reserved label values:

                   i. A value of 0 represents the
                      'IPv4 Explicit NULL Label'.  This label
                      value is only legal at the bottom of the
                      label stack.  It indicates that the label
                      stack must be popped, and the forwarding
                      of the packet must then be based on the
                      IPv4 header.

                  ii. A value of 1 represents the
                      'Router Alert Label'.  This label value is
                      legal anywhere in the label stack except at
                      the bottom.  When a received packet
                      contains this label value at the top of
                      the label stack, it is delivered to a
                      local software module for processing.
                      The actual forwarding of the packet
                      is determined by the label beneath it
                      in the stack.  However, if the packet is
                      forwarded further, the Router Alert Label
                      should be pushed back onto the label stack
                      before forwarding.  The use of this label
                      is analogous to the use of the
                      'Router Alert Option' in IP packets
                      [RFC2113].  Since this label
                      cannot occur at the bottom of the stack,
                      it is not associated with a
                      particular network layer protocol.

                 iii. A value of 2 represents the
                      'IPv6 Explicit NULL Label'.  This label
                      value is only legal at the bottom of the
                      label stack.  It indicates that the label
                      stack must be popped, and the forwarding
                      of the packet must then be based on the
                      IPv6 header.

                  iv. A value of 3 represents the
                      'Implicit NULL Label'.
                      This is a label that an LSR may assign and
                      distribute, but which never actually
                      appears in the encapsulation.  When an
                      LSR would otherwise replace the label
                      at the top of the stack with a new label,
                      but the new label is 'Implicit NULL',
                      the LSR will pop the stack instead of
                      doing the replacement.  Although
                      this value may never appear in the
                      encapsulation, it needs to be specified in
                      the Label Distribution Protocol, so a value
                      is reserved.

                   v. Values 4-15 are reserved.

              * The frame relay label can be either 10-bits or
                23-bits depending on the DLCI field size and the
                upper 22-bits or upper 9-bits must be zero,
                respectively.

              * For an ATM label the lower 16-bits represents the
                VCI, the next 12-bits represents the VPI and the
                remaining bits MUST be zero."
          REFERENCE
             "Multiprotocol Label Switching Architecture,
              RFC3031.

              MPLS Label Stack Encoding, [RFC3032].

              Use of Label Switching on Frame Relay Networks,
              RFC3034.

              MPLS using LDP and ATM VC Switching, RFC3035."
          SYNTAX  Unsigned32 (0..4294967295)

Notes
-----
The entire talk of having GMPLS label greater than (2^24 - 1)does not make sense at all. Removed the references to GMPLS in the MplsLabel TC. The same labels as MPLS labels can be signaled using MPLS or GMPLS signaling.

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--------------------------------------
RFC3811 (draft-ietf-mpls-tc-mib-10)
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Title               : Definitions of Textual Conventions (TCs) for Multiprotocol Label Switching (MPLS) Management
Publication Date    : June 2004
Author(s)           : T. Nadeau, Ed., J. Cucchiara, Ed.
Category            : PROPOSED STANDARD
Source              : Multiprotocol Label Switching
Area                : Routing
Stream              : IETF
Verifying Party     : IESG