Re: [ippm] Magnus Westerlund's Discuss on draft-ietf-ippm-stamp-07: (with DISCUSS and COMMENT)

Henrik Nydell <hnydell@accedian.com> Wed, 11 September 2019 08:30 UTC

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From: Henrik Nydell <hnydell@accedian.com>
Date: Wed, 11 Sep 2019 10:30:06 +0200
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To: Magnus Westerlund <magnus.westerlund@ericsson.com>
Cc: "gregimirsky@gmail.com" <gregimirsky@gmail.com>, "draft-ietf-ippm-stamp@ietf.org" <draft-ietf-ippm-stamp@ietf.org>, "iesg@ietf.org" <iesg@ietf.org>, "tal.mizrahi.phd@gmail.com" <tal.mizrahi.phd@gmail.com>, "ippm-chairs@ietf.org" <ippm-chairs@ietf.org>, "ippm@ietf.org" <ippm@ietf.org>
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Subject: Re: [ippm] Magnus Westerlund's Discuss on draft-ietf-ippm-stamp-07: (with DISCUSS and COMMENT)
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See below for PTP/NTP comment

On Wed, Sep 11, 2019 at 9:53 AM Magnus Westerlund <
magnus.westerlund@ericsson.com>; wrote:

> Hi Greg,
>
> Thanks for the reply. See inline for my comments and response.
>
>
> On Tue, 2019-09-10 at 12:43 -0700, Greg Mirsky wrote:
> > Hi Magnus,
> > thank you for the review and thoughtful, pointed questions. Please
> > find my answers in-line under GIM>> tag.
> >
> > Regards,
> > Greg
> >
> > On Wed, Sep 4, 2019 at 3:54 PM Magnus Westerlund via Datatracker <
> > noreply@ietf.org>; wrote:
> > > Magnus Westerlund has entered the following ballot position for
> > > draft-ietf-ippm-stamp-07: Discuss
> > >
> > > When responding, please keep the subject line intact and reply to
> > > all
> > > email addresses included in the To and CC lines. (Feel free to cut
> > > this
> > > introductory paragraph, however.)
> > >
> > >
> > > Please refer to
> > > https://www.ietf.org/iesg/statement/discuss-criteria.html
> > > for more information about IESG DISCUSS and COMMENT positions.
> > >
> > >
> > > The document, along with other ballot positions, can be found here:
> > > https://datatracker.ietf.org/doc/draft-ietf-ippm-stamp/
> > >
> > >
> > >
> > > -----------------------------------------------------------------
> > > -----
> > > DISCUSS:
> > > -----------------------------------------------------------------
> > > -----
> > >
> > > Two very much discussing discusses. However, I would really like to
> > > hear the
> > > answer to these concerns before clearing.
> > >
> > > 1. Section 4.3: Is the HMAC field size of 16 bytes hard coded? If
> > > there ever
> > > would exist a need to deploy another integrity solution, even if
> > > the actual
> > > algorithm used to construct the tag can be agreed by the
> > > management, there
> > > appear to exist a hard look in to use 16-byte tags. Have this issue
> > > been
> > > considered?
> >
> > GIM>> Indeed, this specification defines the use of only one
> > algorithm and only 16 bytes-long HMAC field. Your question prompted
> > the discussion among authors and we believe that in a future
> > specification it would be feasible to extend supporting a number of
> > algorithms and different lengths of HMAC field both being defined
> > through extension to STAMP YANG data model.
>
> So if I understand this (taking a discussion with Mirja about keeping
> things as simple as possible) the solution is to basically is when need
> arises define a new STAMP version, and then use YANG to coordinate
> which version is used for the measurement. If that is a correct re-
> interpretation of your response then I am fine with it.
>
> > >         2. Section 6:
> > >         The possible impact of the
> > >    STAMP test packets on the network MUST be thoroughly analyzed,
> > > and
> > >    the use of STAMP for each case MUST be agreed by all users on
> > > the
> > >    network before starting the STAMP test session.
> > >
> > >         I assume some potential issues are know, shouldn't they
> > > really be
> > >         listed here in the security consideration to further
> > > motivate why the
> > >         analysis needs to happen.
> >
> > GIM>> This is in reference to using numbers from the User range as
> > the destination port number. Would adding the reference to the case
> > of using the port numbers from the User range address your concern?
> > Or rather refer to Section 4, as it includes more discussion (see
> > below)?
>
> Okay, I don't really care where the discussion happens. But I don't
> find any real discussion and listing of the concerns with using user or
> dynamic ports for STAMP Sessions? With the formulation you use, I would
> expect at least some list of potential concerns that needs to be
> evaluated in the context of the particular usage of STAMP.
>
> > >
> > > -----------------------------------------------------------------
> > > -----
> > > COMMENT:
> > > -----------------------------------------------------------------
> > > -----
> > >
> > >         1. Section 4:
> > >         Before using numbers from the User Ports range, the
> > > possible impact
> > >    on the network MUST be carefully studied and agreed by all users
> > > of
> > >    the network.
> > >
> > >         Is the above sentence missing to list an important
> > > assumption? Is the
> > >         assumption that by using the registred destination port an
> > > operator
> > >         that sees to much STAMP traffic can simply filter it out
> > > and that way
> > >         deal with the traffic, something which is not possible when
> > > using an
> > >         locally decided port? If that is the case, this assumption
> > > should
> > >         probably be noted.
> >
> > GIM>> That is a very good point but our primary motivation for this
> > cautionary note (or strong warning) was that by allowing STAMP to use
> > port numbers from the User range, ports that may be already assigned
> > to protocols, creates a DDOS attack vector. As for the filtering
> > STAMP traffic out, I think that even if the destination port is one
> > from the Dynamic range, for a relatively long test session it can be
> > filtered out.
>
> So if that is the only? concern then write it out. I would expect that
> the higher layer management protocol that creates a measurement session
> to actually ensure that the STAMP endpoint actually have the port
> numbers they attempt to use. Isn't that a reasonable requirement to put
> on the solution?
>
> My thinking with the filtering out concern was that in cases where one
> runs STAMP measurement sessions, if the measurement interfer with
> critical traffic an action for an on-path node that can actually
> identify the STAMP traffic was to filer it out. And that may be
> considered trivial when the well known port is used, but if a user or
> dynamic port is used, then that requries a managment system to provide
> the on-path node with the necessary information, i.e. 3/5 tuple for the
> STAMP flows.
>
>
> > >         2. Section 3 and 4, and 4.1.1: What is a STAMP Session? Is
> > > that a
> > >         measurment session between one specific and sender and a
> > > specific
> > >         reflector for a time duration?  The defenition of the
> > > session do matter
> > >         if one intended to enable a single sender to use multiple
> > > reflectors,
> > >         and if that can be a single session or always multiple
> > > indepdendent
> > >         ones. Would appreciate a definition what a session is. If
> > > it is
> > >         possible to send STAMP traffic using a multicast or
> > > broadcast address
> > >         should be made explicit.
> >
> > GIM>> Your interpretation is correct, STAMP session is implicitly
> > defined as p2p. And that is what reflected in the STAMP YANG model.
> > Would the following text make it clearer:
> > NEW TEXT:
> >    In this document, a measurement session also referred to as
> >    STAMP session, is the session between one specific Session-Sender
> > and
> >    one particular Session-Reflector for a time duration.
>
> Yes, please include that definition. Question would it be clearer to
> replace ".. is the session betweeen .." with ".. is the bi-directional
> packet flows between .."?
>
>
> > >         3.  Section 4.1.1.:
> > >         Timestamp is eight octets long field.  STAMP node MUST
> > > support
> > >       Network Time Protocol (NTP) version 4 64-bit timestamp format
> > >       [RFC5905], the format used in [RFC5357].  STAMP node MAY
> > > support
> > >       IEEE 1588v2 Precision Time Protocol truncated 64-bit
> > > timestamp
> > >       format [IEEE.1588.2008], the format used in [RFC8186].
> > >
> > >         Is the clock source here something that may be relevant or
> > > simply
> > >         information the management functions should capture. I
> > > think there is a
> > >         similar issue to that of RTP faced when it comes to
> > > understand what the
> > >         timestamp actually represent and thus be used correctly.
> > > RTP clock
> > >         source specification is RFC 7273
> > >         (https://datatracker.ietf.org/doc/rfc7273/)
> >
> > GIM>> NTP and PTP encodings have a different interpretation of the
> > Fraction field of the Timestamp field. In my experience, PTP format
> > is native for the data plane, while NTP is more used at the control
> > plane. Original extension to TWAMP has been described in RFC 8186.
>
> I think you missunderstood. When I talk about clock source, I am
> actually referring to identifying the particular clock that the node
> use to derive the included timestamp from.
>
> And likely this is a moot point in this document where the clock source
> information belongs in the management layer, e.g. in the YANG data
> model.
>

In section 4.1.1 of draft-ietf-ippm-stamp there is a definition of the
Z-bit in the error correction field that denotes if the clock source is NTP
or PTP


>
>
> > >         4. Section 4.1:
> > >            Because STAMP supports symmetrical test packets, STAMP
> > > Session-Sender
> > >    packet has a minimum size of 44 octets in unauthenticated mode,
> > > see
> > >    Figure 2, and 112 octets in the authenticated mode, see Figure
> > > 4.
> > >
> > >         The above text implies some potential for UDP payload size
> > > variability
> > >         for the STAMP packets. However, the actual definition
> > > appear to have
> > >         fixed sizes. Can you please clarify if I have missed
> > > something that
> > >         enables the STAMP packet to have variable size?
> >
> > GIM>> I think that the text can be improved by characterizing the
> > listed sizes as "base". The variable length of a test packet in STAMP
> > is supported by using Extra Padding TLV defined in draft-ietf-ippm-
> > stamp-option-tlv. Below is the proposed update:
> > OLD TEXT:
> >    Because STAMP supports symmetrical test packets, STAMP Session-
> > Sender
> >    packet has a minimum size of 44 octets in unauthenticated mode,
> > see
> >    Figure 2, and 112 octets in the authenticated mode, see Figure 4.
> > NEW TEXT:
> >    STAMP supports symmetrical test packets.  The base STAMP Session-
> >    Sender packet has a minimum size of 44 octets in unauthenticated
> >    mode, see Figure 2, and 112 octets in the authenticated mode, see
> >    Figure 4.  The variable length of a test packet in STAMP is
> > supported
> >    by using Extra Padding TLV defined in
> >    [I-D.ietf-ippm-stamp-option-tlv].
> >
> > With the new reference, should I-D.ietf-ippm-stamp-option-tlv be
> > moved to the Normative References list or may remain in the
> > Informative list?
>
> From my perspective, the fact that optional TLV may occur following the
> base headers appears quite important. Here comes a question of
> intention form the WG. Is it intended that one can have STAMP endpoints
> that do not even support receiving packets larger than the base?
>
> In other words there will be two main versions already now, one that
> supports some TLV and can at least handle the TLV skip forward and
> ignore the content and one that will throw a fit over the TLVs? If that
> is not the intention I think the fact that TLV's may occur should be
> moved into this specification and have it as a normative reference.
>
> I guess the answer is that you have backwards comaptibility reasons for
> not allowing TLVs at all in some sessions, or?
>
>
> Cheers
>
> Magnus Westerlund
>
>
> ----------------------------------------------------------------------
> Network Architecture & Protocols, Ericsson Research
> ----------------------------------------------------------------------
> Ericsson AB                 | Phone  +46 10 7148287
> Torshamnsgatan 23           | Mobile +46 73 0949079
> SE-164 80 Stockholm, Sweden | mailto: magnus.westerlund@ericsson.com
> ----------------------------------------------------------------------
>
>
>

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