Re: [Detnet] Regarding the model for Active OAM packet

Loa Andersson <loa@pi.nu> Thu, 20 September 2018 10:14 UTC

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To: Mach Chen <mach.chen@huawei.com>, Greg Mirsky <gregimirsky@gmail.com>
Cc: DetNet WG <detnet@ietf.org>, János Farkas <Janos.Farkas@ericsson.com>, "detnet-chairs@ietf.org" <detnet-chairs@ietf.org>, Stewart Bryant <stewart.bryant@gmail.com>, "matthew.bocci@alcatel-lucent.com" <matthew.bocci@alcatel-lucent.com>
References: <F73A3CB31E8BE34FA1BBE3C8F0CB2AE29267092D@dggeml530-mbs.china.huawei.com> <CA+RyBmX29+Q9y3dXM-PqYm-Nu8KtjYZDs6a-fh_rW5hacSpyRg@mail.gmail.com> <F73A3CB31E8BE34FA1BBE3C8F0CB2AE292672CBB@dggeml530-mbs.china.huawei.com> <d4e45e7d-1001-be64-9ff0-f9ea9a882b77@pi.nu> <F73A3CB31E8BE34FA1BBE3C8F0CB2AE292673B40@dggeml530-mbs.china.huawei.com>
From: Loa Andersson <loa@pi.nu>
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Date: Thu, 20 Sep 2018 18:14:06 +0800
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Archived-At: <https://mailarchive.ietf.org/arch/msg/detnet/mDRiM0OzTJZzt7aTf96ryH3kJek>
Subject: Re: [Detnet] Regarding the model for Active OAM packet
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Mach,

I'd like Stewart or Matthew to look at this, but as I understand it it 
is possible to define a new ACH-type that can do exactly what you want.

/Loa

On 2018-09-20 17:58, Mach Chen wrote:
> Loa,
> 
> GAL is just an OAM indicator, the problem here is that when do DetNet OAM, the d-CW will replaced by ACH or by GAL+ACH. No matter which way is used, to support the replication or elimination, there has to be a sequence number filed. But ACH (as its current defined) does not have such a field.
> 
> My suggestion is to use the reserved field of ACH to carry sequence number of OAM packet,  and for those replication or elimination nodes, they do not have to differentiate whether a packet is OAM packet or a normal packet, they could just treat the right 28 bits of the ACH as the sequence number ( or treat the ACH as the d-CW), then both OAM and replication/elimination can be supported.
> 
> Best regards,
> Mach
> 
>> -----Original Message-----
>> From: detnet [mailto:detnet-bounces@ietf.org] On Behalf Of Loa Andersson
>> Sent: Thursday, September 20, 2018 3:21 PM
>> To: Mach Chen <mach.chen@huawei.com>; Greg Mirsky
>> <gregimirsky@gmail.com>
>> Cc: DetNet WG <detnet@ietf.org>; János Farkas
>> <Janos.Farkas@ericsson.com>; detnet-chairs@ietf.org
>> Subject: Re: [Detnet] Regarding the model for Active OAM packet
>>
>> Mach,
>>
>> If I understand you correctly this is for an LSP in an MPLS network, can you
>> help me understand why GAL does not enough. Given that there might be
>> some minor extensions to GAL because of replication and elimination.
>>
>> /Loa
>>
>> On 2018-09-19 14:31, Mach Chen wrote:
>>> Hi Greg,
>>>
>>> Indeed, there is no DetNet Associated Channel defined in
>>> draft-ietf-detnet-dp-sol-mpls for now, I think there should be.  I
>>> also assume that PW ACH will be used for DetNet OAM.
>>>
>>> Assume that PW ACH will be used for DetNet OAM and the reserved filed
>>> of the PW ACH will be used to carry sequence number for OAM packet.
>>> But
>>>    for PREF, a tricky way is to treat the “Version”+ “Reserved” +
>>> ”Channel type” as the Sequence number, the replication or elimination
>>> nodes do not need to differentiate whether it is a d-CW or  a PW ACH .
>>> This way, OAM can be supported without additional processing and states.
>>>
>>>          0                   1                   2                   3
>>>
>>>          0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0
>>> 1
>>>
>>>
>>> +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>>>
>>>         |0 0 0 1|Verion |    Reserved   |         Channel Type
>>> |
>>>
>>>
>>> +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>>>
>>> Regarding sequence number, there are two ways to generate the
>> sequence
>>> number IMHO:  1) generated by the edge node, but it may need to
>>> configure the start number, or 2) copied from the application-flow (if
>>> there is). If the WG agree with this, the model can be updated reflect
>>> this.
>>>
>>> Best regards,
>>>
>>> Mach
>>>
>>> *From:*Greg Mirsky [mailto:gregimirsky@gmail.com]
>>> *Sent:* Wednesday, September 19, 2018 11:29 AM
>>> *To:* Mach Chen <mach.chen@huawei.com>
>>> *Cc:* János Farkas <Janos.Farkas@ericsson.com>; DetNet WG
>>> <detnet@ietf.org>; detnet-chairs@ietf.org
>>> *Subject:* Re: Regarding the model for Active OAM packet
>>>
>>> Hi Mach,
>>>
>>> thank you for your attention to my comment and the most expedient
>> response.
>>>
>>> I don't find the DetNet Associated Channel defined in
>>> draft-ietf-detnet-dp-sol-mpls and thus I assumed that OAM packets that
>>> follow the data packet encapsulation defined in that draft use PW ACH
>>> as defined in section 5 RFC 4385: True, it includes 8 bits-long
>>> Reserved field that may be defined as OAM Sequence Number but that
>> had
>>> not been discussed. One is certain, existing nodes do not check the
>>> Reserved field. And without a field to hold the sequence number, PREF
>>> will not handle the OAM packets. Another question, additional
>>> processing and amount of state introduced in the fast path by the fact
>>> that OAM's Sequence Number will have different length and location in
>>> d-CW (differentiating cases by the first nibble).
>>>
>>> Now, if we step back from DetnNet in MPLS data plane encapsulation,
>>> why the control-word, as I understand, is configurable? I think that
>>> the Sequence Number is not configurable, nor the first nibble. What do
>>> you think?
>>>
>>> Regards,
>>>
>>> Greg
>>>
>>> On Tue, Sep 18, 2018 at 7:48 PM Mach Chen <mach.chen@huawei.com
>>> <mailto:mach.chen@huawei.com>> wrote:
>>>
>>>      Hi Greg,
>>>
>>>      The MPLS DetNet header is defined as below:
>>>
>>>      grouping mpls-detnet-header {
>>>           description
>>>               "The MPLS DetNet encapsulation header information.";
>>>           leaf service-label {
>>>             type uint32;
>>>             mandatory true;
>>>             description
>>>               "The service label of the DetNet header.";
>>>           }
>>>           leaf control-word {
>>>             type uint32;
>>>             mandatory true;
>>>             description
>>>               "The control word of the DetNet header.";
>>>           }
>>>         }
>>>
>>>      Although do not consider Active OAM when design the above
>>>      mpls-denet-header,  seems that it can cover Active OAM case as well.
>>>      No matter a normal DetNet packet or an Active OAM packet, there
>>>      should be a CW field, just as defined above.
>>>
>>>      For normal DetNet packets, the CW is the d-CW as defined in the
>>>      draft-ietf-detnet-dp-sol-mpls.
>>>
>>>      For OAM packets, the CW is the "DetNet Associated Channel".
>>>
>>>      Best regards,
>>>      Mach
>>>
>>>
>>>      > -----Original Message-----
>>>      > From: detnet [mailto:detnet-bounces@ietf.org <mailto:detnet-
>> bounces@ietf.org>] On Behalf
>>>      Of Greg Mirsky
>>>      > Sent: Wednesday, September 19, 2018 3:17 AM
>>>      > To: János Farkas <Janos.Farkas@ericsson.com
>> <mailto:Janos.Farkas@ericsson.com>>
>>>      > Cc: DetNet WG <detnet@ietf.org <mailto:detnet@ietf.org>>; detnet-
>> chairs@ietf.org
>>>      <mailto:detnet-chairs@ietf.org>
>>>      > Subject: Re: [Detnet] WG adoption poll draft-geng-detnet-conf-yang
>>>      >
>>>      > Hi Janos, et. al,
>>>      > the mpls-detnet-header container is based on the solution described in
>>>      > draft-ietf-detnet-dp-sol-mpls. Analysis of active SFC OAM in the
>> proposed
>>>      > MPLS data plane solution in draft-mirsky-detnet-oam points to the
>> potential
>>>      > problem as result the fact that OAM packet doesn't include d-CW. I
>> believe
>>>      > that this question should be discussed and, if we agree on the problem
>>>      > statement, properly resolved. Until then, I do not support the adoption
>> of
>>>      > the model that may not be capable to support active OAM.
>>>      >
>>>      > Regards,
>>>      > Greg
>>>      > On Tue, Sep 18, 2018 at 12:03 PM Janos Farkas
>> <Janos.Farkas@ericsson.com <mailto:Janos.Farkas@ericsson.com>>
>>>      > wrote:
>>>      > >
>>>      > > Dear all,
>>>      > >
>>>      > > This is start of a two week poll on making
>>>      > > draft-geng-detnet-conf-yang-04 a working group document. Please
>> send
>>>      > > email to the list indicating "yes/support" or "no/do not support".  If
>>>      > > indicating no, please state your reservations with the document.  If
>>>      > > yes, please also feel free to provide comments you'd like to see
>>>      > > addressed once the document is a WG document.
>>>      > >
>>>      > > The poll ends Oct 3.
>>>      > >
>>>      > > Thanks,
>>>      > > János and Lou
>>>      > >
>>>      > > _______________________________________________
>>>      > > detnet mailing list
>>>      > > detnet@ietf.org <mailto:detnet@ietf.org>
>>>      > > https://www.ietf.org/mailman/listinfo/detnet
>>>      >
>>>      > _______________________________________________
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>>>
>>>
>>>
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>>>
>>
>> --
>>
>>
>> Loa Andersson                        email: loa@pi.nu
>> Senior MPLS Expert
>> Bronze Dragon Consulting             phone: +46 739 81 21 64
>>
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-- 


Loa Andersson                        email: loa@pi.nu
Senior MPLS Expert
Bronze Dragon Consulting             phone: +46 739 81 21 64