Re: [Int-area] Discussion about Section 6.1 in draft-ietf-intarea-frag-fragile

"Templin (US), Fred L" <Fred.L.Templin@boeing.com> Fri, 06 September 2019 21:03 UTC

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From: "Templin (US), Fred L" <Fred.L.Templin@boeing.com>
To: Tom Herbert <tom@herbertland.com>, Ole Troan <otroan@employees.org>
CC: Ron Bonica <rbonica=40juniper.net@dmarc.ietf.org>, "int-area@ietf.org" <int-area@ietf.org>, IESG <iesg@ietf.org>, Joel Halpern <joel.halpern@ericsson.com>, "draft-ietf-intarea-frag-fragile@ietf.org" <draft-ietf-intarea-frag-fragile@ietf.org>, Suresh Krishnan <suresh@kaloom.com>, "intarea-chairs@ietf.org" <intarea-chairs@ietf.org>
Thread-Topic: [Int-area] Discussion about Section 6.1 in draft-ietf-intarea-frag-fragile
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Date: Fri, 06 Sep 2019 21:03:24 +0000
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Subject: Re: [Int-area] Discussion about Section 6.1 in draft-ietf-intarea-frag-fragile
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Hi Tom,

> -----Original Message-----
> From: Int-area [mailto:int-area-bounces@ietf.org] On Behalf Of Tom Herbert
> Sent: Friday, September 06, 2019 11:21 AM
> To: Ole Troan <otroan@employees.org>
> Cc: Ron Bonica <rbonica=40juniper.net@dmarc.ietf.org>; int-area@ietf.org; IESG <iesg@ietf.org>; Joel Halpern
> <joel.halpern@ericsson.com>; draft-ietf-intarea-frag-fragile@ietf.org; Suresh Krishnan <suresh@kaloom.com>; intarea-
> chairs@ietf.org
> Subject: Re: [Int-area] Discussion about Section 6.1 in draft-ietf-intarea-frag-fragile
> 
> On Thu, Sep 5, 2019 at 11:33 PM Ole Troan <otroan@employees.org> wrote:
> >
> > Bob, et al,
> >
> > I have two issues with this text.
> >
> > 1) It introduces something new and undescribed in paragraph 2.
> >    "unless they also include mechanisms to detect that IP fragmentation isn't working
> >   reliably."
> >    That seems like hand-waving to me. Suggest deleting.
> >
> > 2) Paragraph 4:
> >    "The risks of IP fragmentation can also be mitigated
> >    through the use of encapsulation, e.g., by transmitting IP fragments
> >    as payloads."
> >
> >    This seems like proposing new unspecified solutions with it's own set
> >    of considerations. IP fragmentation is a general solution to all hosts,
> >    encapsulation is certainly not in every host, and has different
> >    properties with regards to NAT traversal etc. Also if encapsulation
> >    was the answer, other segmentation / reassembly that were tunnel
> >    specific could be developed. Regardless this also amounts of hand-waving
> >    and doesn't seem to offer any advice that can be heeded now.
> >    And of course encapsulation can also exacerbate the problem
> >    by increasing packet size.
> >    Suggest deletion.
> >
> Ole,
> 
> This also makes the implicit and seemingly unproven assumption that
> encapsulation is less fragile than IP fragmentation on the Internet.

With the rise of the middle and network-based (deep) packet inspection, I
think the statement could be considered that all things on the Internet are
potentially fragile or could become so in the future. Certainly we know that
naked IP fragments are filtered over many paths, and we have a strong
intuition that if we clothe them in "innocent-looking" clothing that they will
be far more likely to get through. For example, I don't think UDP port 6080
(or even 8060) are on many middlebox blacklists yet.

> Without the data that shows otherwise, I don't believe there is any
> basis to say that encapsulation is generally a viable alternative.

I don't think gathering data in a snapshot of time today could serve as a
predictor of the state of affairs a few weeks/months/years down the
road from now. But, what we believe is that right here; right now we
are far more likely to get a whole IP/UDP packet that contains an IP
fragment through than we are to get a naked IP fragment through.

I think if we deployed on the Internet today in innocuous headers like
UDP port 6080/8060 we could start getting the word out that IP fragments
carried in these protocols are good - not evil - and the proper way to
transport them. It's like anything else in the Internet in terms of what
middleboxes will pass vs. block; reputation is everything.

> Also, I would note that there was similar text in early versions of
> RFC8200 that encapsulation could be used as a method of allowing
> extension header insertion. That text was taken out because
> encapsulation is not sufficiently standardized or ubiquitous to be
> considered a direct replacement for an IP network layer protocol
> function. The same is true here, encapsulation is not a drop-in
> replacement for IP fragmentation.

No; not a replacement for IP fragmentation but rather a vehicle for
carrying IP fragments. It is still good old IP fragmentation.

Fred

> Tom
> 
> > New text:
> >
> > 6.1.  For Application and Protocol Developers
> >
> >   Developers SHOULD NOT develop new protocols or applications that rely
> >   on IP fragmentation.  When a new protocol or application is deployed
> >   in an environment that does not fully support IP fragmentation, it
> >   SHOULD operate correctly, either in its default configuration or in a
> >   specified alternative configuration.
> >
> >   While there may be controlled environments where IP fragmentation
> >   works reliably, this is a deployment issue and can not be known to
> >   someone developing a new protocol or application.  It is not
> >   recommended that new protocols or applications be developed that rely
> >   on IP fragmentation.  Protocols and applications that rely on IP
> >   fragmentation will work less reliably on the Internet.
> >
> >   Legacy protocols that depend upon IP fragmentation SHOULD be updated
> >   to break that dependency.  However, in some cases, there may be no
> >   viable alternative to IP fragmentation (e.g., IPSEC tunnel mode, IP-
> >   in-IP encapsulation).  Applications and protocols cannot necessarily
> >   know or control whether they use lower layers or network paths that
> >   rely on such fragmentation.  In these cases, the protocol will
> >   continue to rely on IP fragmentation but should only be used in
> >   environments where IP fragmentation is known to be supported.
> >
> >   Protocols may be able to avoid IP fragmentation by using a
> >   sufficiently small MTU (e.g.  The protocol minimum link MTU),
> >   disabling IP fragmentation, and ensuring that the transport protocol
> >   in use adapts its segment size to the MTU.  Other protocols may
> >   deploy a sufficiently reliable PMTU discovery mechanism
> >   (e.g.,PLMPTUD).
> >
> >   UDP applications SHOULD abide by the recommendations stated in
> >   Section 3.2 of [RFC8085].
> >
> >
> > Cheers,
> > Ole
> >
> > > On 6 Sep 2019, at 06:05, Bob Hinden <bob.hinden@gmail.com> wrote:
> > >
> > > Hi,
> > >
> > > Joe and I talked off list.   The result is below.  Changes were to add a sentence in the forth and fifth paragraphs.
> > >
> > > Please review.
> > >
> > > Bob
> > >
> > > ----------
> > >
> > > 6.1.  For Application and Protocol Developers
> > >
> > >   Developers SHOULD NOT develop new protocols or applications that rely
> > >   on IP fragmentation.  When a new protocol or application is deployed
> > >   in an environment that does not fully support IP fragmentation, it
> > >   SHOULD operate correctly, either in its default configuration or in a
> > >   specified alternative configuration.
> > >
> > >   While there may be controlled environments where IP fragmentation
> > >   works reliably, this is a deployment issue and can not be known to
> > >   someone developing a new protocol or application.  It is not
> > >   recommended that new protocols or applications be developed that rely
> > >   on IP fragmentation.  Protocols and applications that rely on IP
> > >   fragmentation will work less reliably on the Internet unless they
> > >   also include mechanisms to detect that IP fragmentation isn't working
> > >   reliably.
> > >
> > >   Legacy protocols that depend upon IP fragmentation SHOULD be updated
> > >   to break that dependency.  However, in some cases, there may be no
> > >   viable alternative to IP fragmentation (e.g., IPSEC tunnel mode, IP-
> > >   in-IP encapsulation).  Applications and protocols cannot necessarily
> > >   know or control whether they use lower layers or network paths that
> > >   rely on such fragmentation.  In these cases, the protocol will
> > >   continue to rely on IP fragmentation but should only be used in
> > >   environments where IP fragmentation is known to be supported.
> > >
> > >   Protocols may be able to avoid IP fragmentation by using a
> > >   sufficiently small MTU (e.g.  The protocol minimum link MTU),
> > >   disabling IP fragmentation, and ensuring that the transport protocol
> > >   in use adapts its segment size to the MTU.  Other protocols may
> > >   deploy a sufficiently reliable PMTU discovery mechanism
> > >   (e.g.,PLMPTUD).  The risks of IP fragmentation can also be mitigated
> > >   through the use of encapsulation, e.g., by transmitting IP fragments
> > >   as payloads.
> > >
> > >   UDP applications SHOULD abide by the recommendations stated in
> > >   Section 3.2 of [RFC8085].
> > >
> > > —————
> > >
> > >
> > >
> > >> On Sep 5, 2019, at 6:18 PM, Joe Touch <touch@strayalpha.com> wrote:
> > >>
> > >> Although this is close, it misses the mark a little on the issue that
> > >> the app may not actually have any control here - or know how or when to
> > >> reduce its MTU. That might be a minor point to add, but is worth adding.
> > >> This isn't just an app layer issue.
> > >>
> > >> Joe
> > >>
> > >> On 9/5/2019 4:45 PM, Ron Bonica wrote:
> > >>> Bob,
> > >>>
> > >>> I think that this is a close to consensus as we are going to get.
> > >>>
> > >>>                                          Ron
> > >>>
> > >>>
> > >>> Juniper Business Use Only
> > >>>
> > >>> -----Original Message-----
> > >>> From: Bob Hinden <bob.hinden@gmail.com>
> > >>> Sent: Thursday, September 5, 2019 2:29 PM
> > >>> To: int-area@ietf.org
> > >>> Cc: Bob Hinden <bob.hinden@gmail.com>; Alissa Cooper <alissa@cooperw.in>; IESG <iesg@ietf.org>; Joel Halpern
> <joel.halpern@ericsson.com>; draft-ietf-intarea-frag-fragile@ietf.org; intarea-chairs@ietf.org; Suresh Krishnan
> <suresh@kaloom.com>
> > >>> Subject: Discussion about Section 6.1 in draft-ietf-intarea-frag-fragile
> > >>>
> > >>> Hi,
> > >>>
> > >>> Based on the discussion, I would like to propose to see if this will resolve the issues raised.   It attempts to cover the issues
> raised.
> > >>>
> > >>> The full section 6.1 is included below, but only the last sentence in the second paragraph changed.
> > >>>
> > >>> Please review and comment.
> > >>>
> > >>> Thanks,
> > >>> Bob
> > >>>
> > >>>
> > >>>
> > >>> 6.1.  For Application and Protocol Developers
> > >>>
> > >>>  Developers SHOULD NOT develop new protocols or applications that rely
> > >>>  on IP fragmentation.  When a new protocol or application is deployed
> > >>>  in an environment that does not fully support IP fragmentation, it
> > >>>  SHOULD operate correctly, either in its default configuration or in a
> > >>>  specified alternative configuration.
> > >>>
> > >>>  While there may be controlled environments where IP fragmentation
> > >>>  works reliably, this is a deployment issue and can not be known to
> > >>>  someone developing a new protocol or application.  It is not
> > >>>  recommended that new protocols or applications be developed that rely
> > >>>  on IP fragmentation.  Protocols and applications that rely on IP
> > >>>  fragmentation will work less reliably on the Internet unless they
> > >>>  also include mechanisms to detect that IP fragmentation isn't working
> > >>>  reliably.
> > >>>
> > >>>  Legacy protocols that depend upon IP fragmentation SHOULD be updated
> > >>>  to break that dependency.  However, in some cases, there may be no
> > >>>  viable alternative to IP fragmentation (e.g., IPSEC tunnel mode, IP-
> > >>>  in-IP encapsulation).  In these cases, the protocol will continue to
> > >>>  rely on IP fragmentation but should only be used in environments
> > >>>  where IP fragmentation is known to be supported.
> > >>>
> > >>>  Protocols may be able to avoid IP fragmentation by using a
> > >>>  sufficiently small MTU (e.g.  The protocol minimum link MTU),
> > >>>  disabling IP fragmentation, and ensuring that the transport protocol
> > >>>  in use adapts its segment size to the MTU.  Other protocols may
> > >>>  deploy a sufficiently reliable PMTU discovery mechanism
> > >>>  (e.g.,PLMPTUD).
> > >>>
> > >>>  UDP applications SHOULD abide by the recommendations stated in
> > >>>  Section 3.2 of [RFC8085].
> > >>>
> > >>> _______________________________________________
> > >>> Int-area mailing list
> > >>> Int-area@ietf.org
> > >>> https://www.ietf.org/mailman/listinfo/int-area
> > >
> >
> > _______________________________________________
> > Int-area mailing list
> > Int-area@ietf.org
> > https://www.ietf.org/mailman/listinfo/int-area
> 
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