Re: [mpls-tp] Comments on draft-nitinb-mpls-tp-on-demand-cv-00

Hi Nitin,

>From this mail thread, can it be assumed that LSP Tracing without IP
Encapsulation does not work for Associated bidirectional LSP's since there
may not be a return LSP path from the responding transit node?

Also when a node receives LSP Echo request w/o IP encapsulation and
replymode "not" set to 4, should it drop the packet or should it try to
respond back with Malformed Echo request error?

Regards,
Mahesh

On Thu, Jun 24, 2010 at 8:59 PM, Mach Chen <mach@huawei.com> wrote:

> Hi Nitin,
>
> Thanks for your reply!
>
> See my reply inline...
>
> --------------------------------------------------
> From: "Nitin Bahadur" <nitinb@juniper.net>
> Sent: Friday, June 25, 2010 1:56 AM
>
> To: "'Mach Chen'" <mach@huawei.com>om>; <mpls-tp@ietf.org>
> Subject: RE: [mpls-tp] Comments on draft-nitinb-mpls-tp-on-demand-cv-00
>
>
> Hi Mach,
>>
>>  Very good example. See more below.
>>
>> IMHO, even if in non-error cases(for associated bidirectional
>>> LSP), the MIPs response may not be able to send the response,
>>>
>>
>> see the figure below:
>>> A---B---C---D---E
>>>  \             /
>>>  F----G------H
>>> A associated bidirectional LSP combined with two
>>> unidirectional LSPs( LSP1:
>>> A->B->C->D->E, and LSP2: E->H->G->F->A), when the trace
>>> request reach at
>>> A->B->C->D->B,
>>> how does node B send the response?
>>>
>>
>> The above case is probably not how things get deployed in transport
>> networks (transport folks can correct me if I am wrong). Transport
>> networks
>> typically have bi-directional physical paths.
>>
>
> IMHO, it's better for transport network to have bi-directioanl phyical
> paths, but it could not exclude the situation where the two directions are
> diverse(at least partially diverse), and this is one of the reasons that
> associated bidrectional LSP required in MPLS-TP.
>
>
>
>> In any case, there are 2 ways for B to send a response back,
>> 1) B sends the response back directly to A via IP or some other
>> encapsulation.
>> 2) B tunnels the packet to E and sends the response back.
>>
>> Option 2 is not practical & insufficient, because if there is a fault at
>> C, then the echo
>> response will never make it back...giving the impression that the fault is
>> at B.
>> Adding the complexity to tunnel the packet to E and then back seems too
>> cumbersome
>> and I don't see a real business case/requirement for the same.
>>
>> Option 1 will not work if there is no IP/MPLS path back to A from B....but
>> I consider that
>> more of a network design issue....
>>
>
> I basically agree with you analyse, so for associated bidirectional LSP,
> the operation is almost the same unidirectional LSP.
>
> One more question: does the tracing result of an associated bidirectional
> LSP inlcude the reverse path, or just one direction? if incluing reverse
> direction, how to process and present the result?
>
> Best regards,
> Mach
>
>
>
>
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