Re: [tcpm] [Last-Call] Opsdir telechat review of draft-ietf-tcpm-yang-tcp-07

Hi Michael

A possible good example of a use case by router vendors of use of the
detailed visibility into the TCP socket in the Yang model is an issue that
has caused outages across the internet related to BGP TCP O window where
the receive window was stuck state and could not write to the receive
buffer and so the BGP session remained in UP state resulting in a major
internet outage.

Operators are now moving towards BGP based MSDC for massive scalability and
no IGP (OSPF or ISIS) for scalability and stability.  As a result of the
motivation and change operationally towards BGP, TCP and all the socket
details is now that much more important to operators as well as now an
significant interest to most vendors.

As well with micro services and Kubernetes with the data center fabric
being moved to compute nodes running hundreds of BGP sessions.

That is the POV we are coming from related to the inner workings and
details of TCP Yang model now applies to router and switch vendors but as
well also compute nodes.

Regards

Gyan

On Mon, Jul 4, 2022 at 3:52 PM Robert Raszuk <robert@raszuk.net> wrote:

> Hi Michael,
>
> Actually I used the URG flag example as this is used by one of the key
> features in one of the major vendor's OS. Ability to see this flag to be
> reported is IMO useful in this very application.
>
> > on-path middleboxes.
>
>
> That is not my concern at all. My focus is to use YANG on the endpoints to
> avoid need to recreate TCP state via TAP captures. Like some of the good
> analyzers allow you to do.
>
>
>
> > many OS kernels don’t use YANG at all.
>
>
> True - but is this the right argument ? Those will not
> benefit irrespective of how small or big YANG model will be shipped.
>
>
> > One could write a lot in a YANG model, but who would actually implement
> that?
>
>
> I would count on network vendors to implement it. And that is my personal
> area of interest. Otherwise I would not care to comment :)
>
> Thx,
> R.
>
> On Mon, Jul 4, 2022 at 9:39 PM Scharf, Michael <
> Michael.Scharf@hs-esslingen.de> wrote:
>
>> Hi Robert,
>>
>>
>>
>> the TCP Urgent Flag is discussed in RFC 6093 and probably not a good
>> example for a TCP-feature relevant for modern applications (RFC 6093 stated
>> more than 10 years ago “new applications SHOULD NOT employ the TCP urgent
>> mechanism”).
>>
>>
>>
>> A modern TCP implementation actually has several windows and running TCP
>> code either measures them in bytes or in segments. That results in quite
>> some differences. So, even for TCP windows there is no simple way to model
>> the actual behavior of widely deployed running code.
>>
>>
>>
>> And the algorithms of a modern TCP stack can imply more than 100
>> parameters. Due to the complexity it is basically impossible to draw the
>> line between “elementary” parameters and implementation-specific ones.
>>
>>
>>
>> All that was discussed in TCPM, and the WG consensus was not to boil the
>> ocean. The very narrow scope of draft-ietf-tcpm-yang-tcp is a result of
>> that discussion in TCPM. I have tried my best to explain the rationale
>> inside the document.
>>
>>
>>
>> It may be possible to publish a more comprehensive TCP YANG model as a
>> follow-up specification. But the first step would be to convince TCPM that
>> this is feasible and that relevant stacks would indeed implement that YANG
>> model.
>>
>>
>>
>> Michael
>>
>>
>>
>>
>>
>>
>>
>> *From:* Robert Raszuk <robert@raszuk.net>
>> *Sent:* Monday, July 4, 2022 9:15 PM
>> *To:* Scharf, Michael <Michael.Scharf@hs-esslingen.de>
>> *Cc:* touch@strayalpha.com; Gyan Mishra <hayabusagsm@gmail.com>; Last
>> Call <last-call@ietf.org>; draft-ietf-tcpm-yang-tcp.all@ietf.org;
>> ops-dir@ietf.org; tcpm@ietf.org
>> *Subject:* Re: [Last-Call] [tcpm] Opsdir telechat review of
>> draft-ietf-tcpm-yang-tcp-07
>>
>>
>>
>> Hi,
>>
>>
>>
>> > Any application can decide to configure TCP parameters as far as
>> possible in the given operation
>>
>> > system, e.g., via the sockets API. That is orthogonal to the internals
>> of the TCP implementation and the TCP protocol.
>>
>>
>>
>> While clients running on top of TCP can configure its parameters I would
>> at least expect to be able to report such values (local and remote) when
>> using the TCP YANG model. For example I can not find the Urgent Flag in the
>> current YANG model. Same for elementary window size of any given
>> connection, same for connection duration, .
>>
>>
>>
>> Inability to do so to me sounds like a half baked model. IMHO it is not
>> ready to be even declared as MVP.
>>
>>
>>
>> Many thx,
>>
>> Robert
>>
>>
>>
>>
>>
>> On Mon, Jul 4, 2022 at 6:06 PM Scharf, Michael <
>> Michael.Scharf@hs-esslingen.de> wrote:
>>
>> Joe, all,
>>
>>
>>
>> „separate protocol specific YANG model” could be the YANG model for BGP,
>> or for any other TCP-based application.
>>
>>
>>
>> Any application can decide to configure TCP parameters as far as possible
>> in the given operation system, e.g., via the sockets API. That is
>> orthogonal to the internals of the TCP implementation and the TCP protocol.
>> The app configuration can be done in YANG or by other means. For the TCP
>> stack, that does not matter.
>>
>>
>>
>> As far as I understand Gyan, the concerns regarding
>> draft-ietf-tcpm-yang-tcp are sorted out already.
>>
>>
>>
>> @all: Please speak up if specific changes are needed in
>> draft-ietf-tcpm-yang-tcp. The authors will have to focus on the IESG
>> feedback.
>>
>>
>>
>> Thanks
>>
>>
>>
>> Michael
>>
>>
>>
>>
>>
>>
>>
>> *From:* touch@strayalpha.com <touch@strayalpha.com>
>> *Sent:* Monday, July 4, 2022 4:38 PM
>> *To:* Gyan Mishra <hayabusagsm@gmail.com>
>> *Cc:* Last Call <last-call@ietf.org>;
>> draft-ietf-tcpm-yang-tcp.all@ietf.org; ops-dir@ietf.org; tcpm@ietf.org
>> *Subject:* Re: [tcpm] Opsdir telechat review of
>> draft-ietf-tcpm-yang-tcp-07
>>
>>
>>
>>
>>
>> —
>>
>> Dr. Joe Touch, temporal epistemologist
>>
>> www.strayalpha.com
>>
>>
>>
>> On Jul 3, 2022, at 10:16 PM, Gyan Mishra <hayabusagsm@gmail.com> wrote:
>>
>>
>>
>> Hi Joe, authors  et all
>>
>>
>>
>> I reviewed the feedback from my earlier review in March and as this model
>> is geared towards BGP primary.
>>
>>
>>
>> To address all of my concerns would be complicated for this Yang model,
>> so the plan is that a separate protocol specific yang model would be a
>> follow on to address all of my concerns.
>>
>>
>>
>> First, there should NEVER be two different YANG models for BGP routers
>> vs. other routers or hosts. TCP is TCP is TCP. If that is an assumption for
>> moving this document forward, TCPM should have a longer discussion about
>> that point specifically.
>>
>>
>>
>> Second, my observations about your requests below stand, regardless of
>> when/where current or future authors might be considering them.
>>
>>
>>
>> Joe
>>
>>
>>
>>
>>
>> On Mon, Jul 4, 2022 at 12:44 AM touch@strayalpha.com <
>> touch@strayalpha.com> wrote:
>>
>> FWIW:
>>
>> > On Jul 3, 2022, at 9:04 PM, Gyan Mishra via Datatracker <
>> noreply@ietf.org> wrote:
>> >
>> > Reviewer: Gyan Mishra
>> > Review result: Not Ready
>> >
>> > This draft provides the Yang data mode for TCP.
>> >
>> > The draft is well written and is almost ready publication.  I verified
>> the FSM
>> > state machine and all states are listed.
>> >
>> > Minor issues:
>> > None
>> >
>> > Major issues:
>> > None
>> >
>> > Nits:
>> > I reviewed the TCP Yang data model and has a question related to the
>> FSM state
>> > machine.
>> >
>> > Would it be possible to specify the TCP Header flags SYN, FIN, ACK, RST
>> of BFD
>> > FSM finite state machine Events and Transition.  I think this would be
>> very
>> > helpful for the TCP Yang model FSM state machine.  For each state you
>> could
>> > specify the flags set.
>>
>> These issues appear to have been raised by you in March during last call
>> review. Some have been addressed by others before; I’ll add my input.
>>
>> The YANG model represents information about the current TCP connection.
>> It is not (and should not be confused with) a specification of the protocol.
>>
>> Further, flags are associated with messages that cause state transitions,
>> not states (i.e., the FSM is a Mealy machine, not a Moore machine). There
>> is no “flags set for each state”.
>>
>> >
>> http://tcpipguide.com/free/t_TCPOperationalOverviewandtheTCPFiniteStateMachineF-2.htm
>>
>> That page has errors and is not consistent with RFC793 (or it’s pending
>> -bis update). E.g., FIN stands for “finis” (latin for “end”), not “finish”.
>>
>> > I think the TCP TCB (TCP Control Block) is missing in the Yang model.
>> This is
>> > important for troubleshooting TCP connection state.
>>
>> RFC793 (and -bis) indicate that the STATUS command, which might return
>> similar information, is optional.
>>
>> If there is connection information returned, I do not think it should be
>> the TCB; that is an implementation-dependent parameter, not a universal
>> property of TCP connections. As others have stated in previous responses to
>> you review, the common subset of the TCB is already contained.
>>
>> I.e., I think the YANG model represents TCP information. It is not - and
>> should not be confused with - a troubleshooting tool.
>>
>> Joe
>>
>> --
>>
>> <http://www.verizon.com/>
>>
>> *Gyan Mishra*
>>
>> *Network Solutions Architect *
>>
>> *Email **gyan.s.mishra@verizon.com* <gyan.s.mishra@verizon.com>
>>
>> *M 301 502-1347*
>>
>>
>>
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>>
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>>
>> --

<http://www.verizon.com/>

*Gyan Mishra*

*Network Solutions A**rchitect *

*Email gyan.s.mishra@verizon.com <gyan.s.mishra@verizon.com>*

*M 301 502-1347*