RFC 4717, "Encapsulation Methods for Transport of Asynchronous Transfer Mode (ATM) over MPLS Networks", December 2006

Errata ID: 2919
Status: Rejected
Type: Technical
Publication Format(s) : TEXT
Reported By: Alfred Hoenes
Date Reported: 2007-10-17
Rejected by: Stewart Bryant
Date Rejected: 2011-08-05

(7d)  Improper use of RFC 2119 keywords

According to RFC 2119, 'MUST' requirements do not admit exceptions.
If exceptional behavior is to be admitted via 'MAY' clauses, the
generally preferred behavior must be specified with 'SHOULD'.

Thus in the light of the explanation at the bottom of page 20
-- quoted and clarified above in (7c) --, the two bullets on top
of page 21,

     * VPI

|      The ingress router MUST copy the VPI field from the incoming cell
       into this field.  For particular emulated VCs, the egress router
       MAY generate a new VPI and ignore the VPI contained in this
       field.

     * VCI

|      The ingress router MUST copy the VCI field from the incoming ATM
       cell header into this field.  For particular emulated VCs, the
       egress router MAY generate a new VCI.

should say:

     * VPI

|      The ingress router SHOULD copy the VPI field from the incoming
       cell into this field.  For particular emulated VCs, the egress
       router MAY generate a new VPI and ignore the VPI contained in
       this field.

     * VCI

|      The ingress router SHOULD copy the VCI field from the incoming
       ATM cell header into this field.  For particular emulated VCs,
       the egress router MAY generate a new VCI.

Notes:

This is section 7(d) From erratum 999
--VERIFIER NOTES--
The MUST and the MAY refer to the behavior of different PW entities (ingress and egress router respectively), thus the original text is correct.

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