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RFC 5601, "Pseudowire (PW) Management Information Base (MIB)", July 2009

Source of RFC: pwe3 (int)

Errata ID: 4069
Status: Verified
Type: Technical
Publication Format(s) : TEXT

Reported By: Alexander ("Sasha") Vainshtein
Date Reported: 2014-08-05
Verifier Name: Brian Haberman
Date Verified: 2014-08-06

Section 12 says:

 pwAttachedPwIndex OBJECT-TYPE
     SYNTAX        PwIndexOrZeroType
     MAX-ACCESS    read-create
     STATUS        current
     DESCRIPTION
         "If the PW is attached to another PW instead of a local
          native service, this item indicates the pwIndex of the
          attached PW.  Otherwise, this object MUST
          be set to zero.  Attachment to another PW will have no
          PW specific entry in any of the service MIB modules."
     DEFVAL { 0 }
     ::= { pwEntry 10 }

It should say:

 pwAttachedPwIndex OBJECT-TYPE
     SYNTAX        PwIndexOrZeroType
     MAX-ACCESS    read-create
     STATUS        current
     DESCRIPTION
          "If the PW is attached to another PW instead of a local
           native service, this item indicates the pwIndex of the
           attached PW.  Otherwise, this object MUST
           be set to zero.  Attachment to another PW will have no
           PW specific entry in any of the service MIB modules.
           This object may be modified only when the value of
           the associated pwAdminStatus object is down(2), and
           the associated pwOperStatus object has value down(2)
           or notPresent(5) such that the row in the pwTable
           represents an inactive PW."
     DEFVAL { 0 }
     ::= { pwEntry 10 }

Notes:

Description of the pwEntry object in the same RFC states that "The read-create objects in this table are divided into
three categories:
1) Objects that MUST NOT be changed after row activation.
These are objects that define basic properties of the
PW (for example type, destination, etc.).
2) Objects that MAY be changed when the PW is
defined as not active. A change of these objects involves
re-signaling of the PW or it might be traffic affecting.
PW not active is defined as one of the following
conditions:
a) The pwRowStatus is notInService(2).
b) The pwRowStatus is notReady(3).
c) The pwAdminStatus is down(2).
If the operator needs to change one of the values for an
active row, the operator can either set the pwRowStatus to
notInService(2) or set pwAdminStatus to down(2).
Signaling (or traffic) is initiated again upon setting
the pwRowStatus to active(1) or setting the pwAdminStatus
to up(1) or testing(3), respectively.
3) Objects that MAY be changed at any time."

In further states (in tthe same description) that "By default, all the read-create objects MUST NOT be changed after row activation, unless specifically indicated in the individual object description."

pwAttachedPwIndex object is used to stitch a couple of PWs represented by two different rows in the pwTable, with the pwAttachedPwIndex value in the row representing one of them set to the pwIndex of the other one and vice versa.
Since there is no way in the SMIv2 paradigm to create two rows in the same table
in a single atomic operation, setting a this attribute in a pair of rows is only
possible when both are created. In order to do that, read-create access mode of
the pwAttachedPwIndex object has to be interpreted as ability to set its value
when the row represents an inactive PW.
In accordance with the quoted description, such an interpretation must be
explicitly specified in the description of this object.

Such a specification is missing in the current text, hence the default
interpretation of the read-create access mode is holds.
Proposed text fixes this problem.

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