Re: [mpls-tp] Demultiplexing to BFD sessions

[Greg Mirsky <[e-mail]>]

Dear Mach,
you'll recall that the first versions of MPLS-TP Proactive CC/CV were based
on work of BFD WG for multipoint network. If my understanding of it correct
BFD session is unidirectional and that required change to BFD Base in regard
to session de-multiplexing. At the last IETF we had discussion and
presentation on how  BFD base can be ran as unidirectional - by source
setting its Required Min RX Interval to zero. As result, the remote node
must not send any periodic BFD control packet. That is what I've referred in
my earlier comment. And if we take in consideration that MPLS-TP OAM must be
able to be instantiated, function without Control Plane, then this mode must
be configurable by NMS, perhaps even without assistance of LSP Ping
bootstrapping BFD session over LSP. But that, I think, is outside of this
discussion.

Regards,
Greg

On Fri, Jun 11, 2010 at 7:22 PM, Mach Chen <[e-mail]> wrote:

> Hi Greg and Shahram,
>
> Thanks for your response!
>
> I have a little bit confusion about unidirectional and bidirectional BFD
> session (and I failed to find where have these definitions). Do you mean
> that unidirectional BFD session only has forward path and no return path? My
> understanding about a BFD session is that it should have both forward and
> return paths, and if this is true and assume to setup separate BFD session
> for each direction of an associated bidirectional LSP, then the PEs of the
> LSP will failed to demultiplex the BFD sessions.
>
> Best regards,
> Mach
>
> --------------------------------------------------
> From: "Greg Mirsky" <[e-mail]>
> Sent: Saturday, June 12, 2010 3:02 AM
> To: "Shahram Davari" <[e-mail]>
> Cc: "Mach Chen" <[e-mail]>om>; "Mukund Mani" <[e-mail]>om>;
> <[e-mail]>
>
> Subject: Re: [mpls-tp] Demultiplexing to BFD sessions
>
>  Hi Shahram,
>> yes, we need to settle on terminology related to protection.
>> It was discussed and presented at the last IETF meeting how bi-directional
>> BFD session easily can operate in, effectively, unidirectional mode. I
>> think
>> that operating BFD session in this mode is applicable to unidirectional
>> and
>> associated bi-directional p2p LSPs.
>>
>> Regards,
>> Greg
>>
>> On Fri, Jun 11, 2010 at 11:54 AM, Shahram Davari <[e-mail]
>> >wrote:
>>
>>   Hi Greg,
>>>
>>>
>>>
>>> I assume by independent protection mode you mean unidirectional
>>> protection.
>>> If unidirectional protection is required, then it is simpler to not use
>>>  bidirectional BFD session.
>>>
>>>
>>>
>>> Regards,
>>>
>>> Shahram
>>>
>>>
>>>
>>> *From:* Greg Mirsky [mailto:[e-mail]]
>>> *Sent:* Friday, June 11, 2010 11:18 AM
>>> *To:* Shahram Davari
>>> *Cc:* Mach Chen; Mukund Mani; [e-mail]
>>>
>>> *Subject:* Re: [mpls-tp] Demultiplexing to BFD sessions
>>>
>>>
>>>
>>> Dear Shahram,
>>> assume one BFD session is applied to an associated bi-directional LSP.
>>> Then
>>> failure in one direction will bring the session in Down state which is
>>> not
>>> desired behavior for independent protection mode. Thus, I think, need for
>>> two BFD, in essence unidirectional, sessions.
>>>
>>> Regards,
>>> Greg
>>>
>>> On Fri, Jun 11, 2010 at 11:03 AM, Shahram Davari <[e-mail]>
>>> wrote:
>>>
>>> Hi,
>>>
>>> Why would one need to run more than one BFD session over an LSP?
>>>
>>> Thanks,
>>> Shahram
>>>
>>>
>>> -----Original Message-----
>>> From: [e-mail] [mailto:[e-mail]] On
>>> Behalf
>>> Of Mach Chen
>>> Sent: Friday, June 11, 2010 3:05 AM
>>> To: Mukund Mani; [e-mail]
>>> Subject: Re: [mpls-tp] Demultiplexing to BFD sessions
>>>
>>> Hi Mukund,
>>>
>>> I also have the same question about this.
>>>
>>> As to the BFD discriminator, IMHO, we should keep using it as it be,
>>> because
>>> it may not be enough to demultiplex the BFD session only based on the
>>> label,
>>> this is especially true when there are more than two BFD sessions over
>>> the
>>> LSP.
>>>
>>> BTW, it seems that explicit null label distribution is not excluded (and
>>> IMHO it should be excluded as PHP) in MPLS-TP (do I miss something?) ,
>>> and
>>> it is one of the issues that LSP-Ping for BFD session bootstrap is trying
>>> to
>>> reslove.
>>>
>>> Best regards,
>>> Mach
>>>
>>> --------------------------------------------------
>>> From: "Mukund Mani" <[e-mail]>
>>> Sent: Friday, June 11, 2010 2:24 PM
>>> To: <[e-mail]>
>>> Subject: [mpls-tp] Demultiplexing to BFD sessions
>>>
>>> > Hi TP-Group
>>> > **
>>> > *draft-ietf-mpls-tp-lsp-ping-bfd-procedures-00 *states in Section 3
>>> >
>>> > "When using BFD over MPLS-TP LSPs, the BFD discriminator MUST either be
>>> > signaled via LSP-Ping or be statically configured."
>>> >
>>> > *draft-ietf-mpls-tp-bfd-cc-cv-00 *states in Section 3.5.6
>>> >
>>> > "MPLS labels at peer MEPs are used to provide context for the received
>>> BFD
>>> > packets."
>>> >
>>> > As I understand from the statement in the CC/CV draft, since
>>> discriminator
>>> > values are not required for demultiplexing to the BFD session anymore,
>>> > we
>>> > will not need LSP Ping to bootstrap BFD session for TP LSP.
>>> >
>>> > But *draft-ietf-mpls-tp-lsp-ping-bfd-procedures-00 *specifies that LSP
>>> > Ping
>>> > can also be used to signal BFD discriminator.
>>> >
>>> > So is LSP Ping still really needed in the context of BFD over MPLS-TP?
>>> >
>>> > Also as a part of MPLS-TP OAM could somebody explain why such a >
>>> deviation
>>> > is
>>> > taken from the BFD-BASE mode of demultiplexing which even BFD-MPLS uses
>>> > (discriminator values instead of MPLS labels), but MPLS-TP goes in for
>>> > demultiplexing using labels....
>>> >
>>> > Could somebody please clarify this..?
>>> >
>>> >
>>> > With Regards
>>> > Mukund
>>> > <http://tools.ietf.org/html/draft-ietf-mpls-tp-bfd-cc-cv-00>
>>> >
>>>
>>>
>>>
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>>