Re: [ippm] Call for adoption of PM on LAG

Greg Mirsky <gregimirsky@gmail.com> Sat, 10 September 2022 05:51 UTC

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From: Greg Mirsky <gregimirsky@gmail.com>
Date: Sat, 10 Sep 2022 07:51:32 +0200
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To: Lu Yunyang <luyy@unitechs.com>
Cc: Marcus Ihlar <marcus.ihlar=40ericsson.com@dmarc.ietf.org>, IETF IPPM WG <ippm@ietf.org>
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Subject: Re: [ippm] Call for adoption of PM on LAG
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Hi Yunyang Lu,
thank you for your thoughtful arguments. Please find my follow-up notes
in-lined below under the GIM2>> tag.

Regards,
Greg

On Fri, Sep 9, 2022 at 12:52 PM Lu Yunyang <luyy@unitechs.com> wrote:

> Hi Greg,
> I think interoperability between STAMP and TWAMP Light is more than a
> straghtforward extension.
> The idea that STAMP and TWAMP Light are able to interwork with each other
> is based on two doctrines:
> 1) both protocols work in simple sender-reflector mode, without
> additional server or client roles defined in original TWAMP.
> 2) the packet formats from sender and reflector sides are exactly the same
> for both protocols in unauthenticated mode.
> Besides, RFC8762 states that ANY STAMP extensions will be ignored and
> treated as plain Packet Padding field when communicating with a TWAMP Light
> counterpart.
>
GIM2>> Agreed.

> Since all member links in LAG share same IP address and test sessions
> usually use same port number across these member links, two new fields
> (Sender / Reflector Micro-session ID) have been introduced as distinguisher
> to identify different sessions.
>
GIM@>> Here, I will point out that "usually" doesn't mean "required". An
operator can discover which protocol performs which role and configure
individual test sessions per LAG member link accordingly.

> However, PM on LAG has different implementations for STAMP and TWAMP
> Light.
>
GIM2>> I might have not been clear in earlier notes. I think that the
protocol interworking over LAG can be handled as a set of independent test
sessions per each LAG member link. None of the discussed LAG-specific
extensions should be invoked. True, it is not guaranteed that an arbitrary
implementation of the Session-Reflector will transmit a reflected packet
over the same LAG member link as the received test packet. Thus I agree
with you that in a general case, test results in the protocol interworking
environment could be uncertain, difficult to interpret.

> On sender side, Micro-session IDs are placed right after Error Estimate
> field in TWAMP packet, occupying part of original padding field defined in
> RFC4656/5357; while on reflector side Sender and Reflector Micro-session
> IDs are placed after Sender Error Estimate and Sender TTL, respectively. For
> STAMP, a new TLV has been requested to carry LAG test session info and
> should be appended to the end of original packet by RFC8972. As a result,
> the Micro-session ID carried by TWAMP packet falls in padding area if
> treated as STAMP packet, and vice versa. If a LAG test session has been
> deploy in hybrid mode, a regular reflector packet might be sent back in
> response to a micro-session sender packet from a specific LAG member
> following the procedure described in RFC8762, which is absolutely not a
> goal of the new proposal. Even if the sender node discards the response due
> to session mismatch, test packets will continue to transfer without manual
> interruption from network operator, making it potentially hazardous.
> Personally, I think STAMP and TWAMP Light for PM on LAG are not quite
> interoperable at current stage, and no operators will actually deploy in
> this way. But, as a standard protocol, we must consider backward
> compatibility with existing implementations. By extending PM from L3 links
> to LAG members, we are not supposed to annul the original STAMP / TWAMP
> Light interoperability defined in RFC8762. Therefore, it is necessary to
> clarify the hybrid scenario to avoid unexcepted outcome.
>
GIM2>> I agree with your conclusion that the hybrid use of active test
protocols is undesirable, and is not recommended. It is a very good idea to
state that clearly in the document. The same, I think, applies to an
environment that uses, for example, implementations of STAMP that support
and doesn't support draft-li-ippm-stamp-on-lag. It seems like this is a
general outcome for incremental deployment of a particular extension. What
do you think?

Regards,
Greg

> Best regards,
> Yunyang Lu
>
> *From:* Greg Mirsky <gregimirsky@gmail.com>
> *Date:* 2022-09-09 14:50
> *To:* Lu Yunyang <luyy@unitechs.com>
> *CC:* Marcus Ihlar <marcus.ihlar=40ericsson.com@dmarc.ietf.org>; IETF
> IPPM WG <ippm@ietf.org>
> *Subject:* Re: [ippm] Call for adoption of PM on LAG
> Hi Yungyang Lu,
> thank you for supporting our work and your thoughtful questions. The
> scenario you've presented is realistic and we believe that our proposal can
> address it. We'll describe handling of this interoperability scenario in
> the future version of the draft.  Please find my notes in-lined below under
> the GIM>> tag.
>
> Regards,
> Greg
>
> On Wed, Sep 7, 2022 at 11:49 AM Lu Yunyang <luyy@unitechs.com> wrote:
>
>> Hi WG,
>>
>>
>>
>> I support the adoption of these drafts. PM on LAG could solve some
>> essential problem for provider and enterprise level network operation.
>>
>>
>> Besides, I think it's necessary to add some clarification for
>> interoperability betweet STAMP and TWAMP-Light, as those stated in RFC8762.
>> Several issues should be considered:
>>
>> 1)  whether STAMP sender / TWAMP-Light reflector and TWAMP-Light sender /
>> STAMP reflector combinations can be used for PM on LAG.
>>
> GIM>> I think that both scenarios can be supported, although that would
> expect more from STAMP implementation as well as more configuration by an
> operator to use STAMP-TWAMP Light interoperability principles described in
> Section 4.6 of RFC 8762 <https://datatracker.ietf.org/doc/rfc8762/>. As a
> result, each of LAG member links will be configured as a separate test
> session.
>
>> 2)  any protocol modifaction or restriction for such measurements.
>>
> GIM>> It seems like this scenario would require more operational effort
> but without specific protocol extensions. What do you think?
>
>> 3)  other considerations that may involve, like security and
>> compatibility with other TWAMP / STAMP extensions.
>>
> GIM>> Thank you for this suggestion! We'll certainly work on adding text
> addressing security and interworking with other STAMP extensions.
>
>>
>>
>> Best regards,
>>
>> Yunyang Lu
>>
>>
>> *发件人:* ippm <ippm-bounces@ietf.org> *代表 *Marcus Ihlar
>> *发送时间:* 2022年9月2日 00:44
>> *收件人:* IETF IPPM WG (ippm@ietf.org) <ippm@ietf.org>
>> *主题:* [ippm] Call for adoption of PM on LAG
>>
>>
>>
>> Hello IPPM,
>>
>> This email starts an adoption call in the IPPM working group for the
>>  draft-li-ippm-stamp-on-lag and draft-li-ippm-otwamp-on-lag documents.
>> These documents extend STAMP, OWAMP and TWAMP to support performance
>> measurements on member links of a Link Aggregation Group.
>>
>>
>>
>> The first draft specifies an extension to STAMP and can be found here:
>>
>> https://datatracker.ietf.org/doc/draft-li-ippm-stamp-on-lag/
>>
>> https://datatracker.ietf.org/doc/html/draft-li-ippm-stamp-on-lag/
>>
>>
>>
>> The second draft specifies extensions to OWAMP and TWAMP and can be found
>> here:
>>
>> https://datatracker.ietf.org/doc/draft-li-ippm-otwamp-on-lag/
>>
>> https://datatracker.ietf.org/doc/html/draft-li-ippm-otwamp-on-lag/
>>
>>
>>
>> Please reply to this email by *Thursday September 15*, to indicate
>> whether you support adoption of these documents.
>>
>>
>>
>> BR
>>
>> Marcus & Tommy
>> _______________________________________________
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>> ippm@ietf.org
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>>
>