On Wed, Mar 15, 2017 at 3:47 AM, Suresh Krishnan
<suresh(_dot_)krishnan(_at_)ericsson(_dot_)com> wrote:
Thanks to everyone who commented during the IETF Last Call of
draft-ietf-6man-rfc2460bis-08. The IETF last call discussion for this draft
was mainly focused around the text in Section 4 that discusses the handling
of extension headers. The biggest concern raised was that the current text is
ambiguous on whether header insertion is allowed on intermediate nodes or
not. There were some people arguing that an explicit prohibition is not
necessary as the text is already clear, while others believed that explicitly
listing the prohibitions will minimize any misunderstandings in the future.
There was also a small number of people who wanted to explicitly allow header
insertion and describe how to do it, but this was clearly out of scope for
this draft (but may be in scope for future work in 6man). Overall, no one
argued against the fact that the intent of the text in RFC2460 was to forbid
insertion of extension headers on any other node but the source of the
packet. The only ar!
gument made against adding clarifying text was that the text was already
clear. Given this, I believe there is consensus to add explicit text about
header insertion into the draft before it progresses further. I have discussed
this with the editor and the document shepherd and would like to propose the
following text change.
OLD (from -08):
The insertion of Extension Headers by any node other than the source
of the packet causes serious problems. Two examples include breaking
the integrity checks provided by the Authentication Header Integrity
[RFC4302], and breaking Path MTU Discovery which can result in ICMP
error messages being sent to the source of the packet that did not
insert the header, rather than the node that inserted the header.
One approach to avoid these problems is to encapsulate the packet
using another IPv6 header and including the additional extension
header after the first IPv6 header, for example, as defined in
[RFC2473]
With one exception, extension headers are not processed by any node
along a packet's delivery path, until the packet reaches the node (or
each of the set of nodes, in the case of multicast) identified in the
Destination Address field of the IPv6 header...
NEW:
With one exception, extension headers are not examined, processed,
inserted, or deleted by any node along a packet's delivery path,
until the packet reaches the node (or each of the set of nodes, in
the case of multicast) identified in the Destination Address field of
the IPv6 header...
I have some concerns with how that sentence AND the following note
comes together:
" With one exception, extension headers are not examined, processed,
inserted, or deleted by any node along a packet's delivery path,
until the packet reaches the node (or each of the set of nodes, in
the case of multicast) identified in the Destination Address field of
the IPv6 header. Note: If an intermediate forwarding node examines
an extension header for any reason, it must do so in accordance with
the provisions of [RFC7045]. "
I'm afraid that the lack of the normative language strikes back..
If 'are not examined" is to be interpreted as RFC2119 'MUST NOT',
then the following note conflicts with that statement. 'A node MUST
NOT examine EHs
but if it does it must do it as per RFC7045' - it is extremely controversial.
If ''are not examined" is to be read as RFC2119 'SHOULD NOT' then I
have a very good news for
those who would still like to insert/delete EHs: they can do it as
long as they have
"valid reasons in particular circumstances when the particular
behavior is acceptable or even useful, but the full
implications should be understood and the case carefully weighed
before implementing any behavior described with this label.".
But from today's presentation I've got an impression that the
intention of this text was actually to prohibit EH insertion
(the sildes say 'no one argued against the fact that the intent of the
text in RFC2460
was to forbid insertion of extension headers on any other node but the source
of the packet.).
So to summarize: the proposed text either explicitly prohibits the
examination (and then it contradicts the next sentence and we need to
do smth with the note and RFC7045) OR it allows EH insertion - it
depends how the text is interpreted.
--
SY, Jen Linkova aka Furry