Subject: [Softwires] [Errata Verified] RFC6333 (5847)

From: RFC Errata System <[email-masked]>
Date: Mon, 17 May 2021 00:57:08 -0700 (PDT)

The following errata report has been verified for RFC6333,
"Dual-Stack Lite Broadband Deployments Following IPv4 Exhaustion". 

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You may review the report below and at:
https://www.rfc-editor.org/errata/eid5847

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Status: Verified
Type: Technical

Reported by: Mikael Abrahamsson <[email-masked]>
Date Reported: 2019-08-26
Verified by: Eric Vyncke (IESG)

Section: 5.3

Original Text
-------------
   However, as not all service providers will be able to increase their
   link MTU, the B4 element MUST perform fragmentation and reassembly if
   the outgoing link MTU cannot accommodate the extra IPv6 header.  The
   original IPv4 packet is not oversized.  The packet is oversized after
   the IPv6 encapsulation.  The inner IPv4 packet MUST NOT be
   fragmented.  Fragmentation MUST happen after the encapsulation of the
   IPv6 packet.  Reassembly MUST happen before the decapsulation of the
   IPv4 packet.  A detailed procedure has been specified in [RFC2473]
   Section 7.2.

Corrected Text
--------------
   However, as not all service providers will be able to increase their
   link MTU, the B4 element MUST perform fragmentation and reassembly if
   the outgoing link MTU cannot accommodate the extra IPv6 header.  The
   original IPv4 packet is not oversized.  The packet is oversized after
   the IPv6 encapsulation.  The inner IPv4 packet MUST NOT be
   fragmented.  Fragmentation MUST happen after the encapsulation of the
   IPv4 packet in the IPv6 packet.  Reassembly of the IPv6 packet MUST happen before the decapsulation of the
   IPv4 packet.  A detailed procedure has been specified in [RFC2473]
   Section 7.2 following point b) and ignoring the DF-bit setting.

Notes
-----
I do not have a corrected text. The above text doesn't say what RFC2473 section 7.2 says, so... what should it be? RFC2473 7.2 says to use the DF bit and decide whether to inner fragment or drop+send ICMP error. The above text seems to make normative statements that counter at least the DF=1 case in RFC2473 7.2. Also the text above says "Fragmentation MUST happen after the encapsulation of the IPv6 packet.". The IPv6 packet isn't encapsulated, so that sentence should be changed?

--- Verifier note ---
Following the discussion in https://mailarchive.ietf.org/arch/msg/softwires/bBQT97R7p1Ho4cUZIP2MFU5ZYJ4/ , the original intent is to avoid fragmenting the IPv4 packet before encapsulation.

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RFC6333 (draft-ietf-softwire-dual-stack-lite-11)
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Title               : Dual-Stack Lite Broadband Deployments Following IPv4 Exhaustion
Publication Date    : August 2011
Author(s)           : A. Durand, R. Droms, J. Woodyatt, Y. Lee
Category            : PROPOSED STANDARD
Source              : Softwires
Area                : Internet
Stream              : IETF
Verifying Party     : IESG