Re: [Pce] PCEP ERO

["Adrian Farrel" <[e-mail]>]

Hi Igor,

Why don't you put the address of NE X in the ERO? You wouldn't even need to say
loose (unless it was genuinely a loose hop).

Now, maybe you are concerned that, having decided which i/f you want to exit by,
there is a risk that you would reach NE X by that interface. Well, that is ever
so slightly possible, but:

- It seems incredibly unlikely that the out interface you are so determined to
use could accidentally become the in interface. If that happened then you would
already have reached the downstream node that you wanted to reach. Uck. Sounds
like a bit of bad path computation!

- You could use path exclusions to make sure that doesn't happen.

BTW...
Is it time to move this discussion to CCAMP where signaling people can discuss
what you are suggesting?

Adrian

> -----Original Message-----
> From: Igor Bryskin [mailto:[e-mail]]
> Sent: 17 June 2014 13:11
> To: Zhangxian (Xian); [e-mail]; 'Dhruv Dhody'; 'Julien Meuric'
> Cc: [e-mail]
> Subject: RE: [Pce] PCEP ERO
> 
> Hi Xian,
> 
> Here is my problem. What if I want my path to go through NE X  and exit it via
> interface Y but do not care on which interface the path enters the NE X?
> What I was saying is that just like we have the LOOSE flag, we could've had
"OUT"
> flag, which would solve all kinds of ambiguities.
> 
> Igor
> 
> -----Original Message-----
> From: Zhangxian (Xian) [mailto:[e-mail]]
> Sent: Monday, June 16, 2014 10:17 PM
> To: Igor Bryskin; [e-mail]; 'Dhruv Dhody'; 'Julien Meuric'
> Cc: [e-mail]
> Subject: RE: [Pce] PCEP ERO
> 
> Hi, Igor,
> 
>   I think you raise up a good question.
> 
>   Just wonder if the text in Section 6.1.2 of RFC4990 (copied below) touch
upon
> the very same problem and provide some guidance?
> 
> --------Section 6.1.2 of RFC4990
> There are two differences between Loose and Strict subobjects.
> 
>    o  A subobject marked as a loose hop in an ERO must not be followed
>       by a subobject indicating a label value [RFC3473].
> 
>    o  A subobject marked as a loose hop in an ERO should never include
>       an identifier (i.e., address or ID) of the outgoing interface.
> 
>    There is no way to specify in an ERO whether a subobject identifies
>    an incoming or outgoing TE link.  Path computation must be performed
>    by an LSR when it encounters a loose hop in order to resolve the LSP
>    route to the identified next hop.  If an interface is specified as a
>    loose hop and is treated as an incoming interface, the path
>    computation will select a path that enters an LSR through that
>    interface.  If the interface was intended to be used as an outgoing
>    interface, the computed path may be unsatisfactory and the explicit
>    route in the ERO may be impossible to resolve.  Thus a loose hop that
>    identifies an interface should always identify the incoming TE link
>    in the data plane.
> -----------------
> 
> Regards,
> Xian
> 
> 
> 
> -----Original Message-----
> From: Pce [mailto:[e-mail]] On Behalf Of Igor Bryskin
> Sent: 2014年6月16日 20:23
> To: [e-mail]; 'Dhruv Dhody'; 'Julien Meuric'
> Cc: [e-mail]
> Subject: Re: [Pce] PCEP ERO
> 
> Hello,
> You are right Julien and Adrian, this is a very old issue. One thing that has
been
> missing IMO is a flag in a numbered/unnumbered link ERSO indicating whether
> the indicated side of the link is outbound or inbound wrt the path direction
from
> its source to destination. The lack of said flag has been especially a problem
when
> combined with the LOOSE flag. Consider, for example, the situation when a
> 1.1.24.1/loose is found in the ERO. If 1.1.24.1 interface is meant to be
inbound,
> the path should *enter* the NE that terminates the interface. However, If
> 1.1.24.1 interface is meant to be outbound, the path should *exit*the said NE.
> So, if the ERO is specified as a path computation constraint, the PCE may
produce
> very different resulting paths depending on the PCE's assumptions/
> interpretations. The introduction of said flag would resolve the ambiguity and
> provide the flexibility (e.g. Druv is talking about) for the ERO encoding.
> 
> Regards,
> Igor
> 
> 
> -----Original Message-----
> From: Pce [mailto:[e-mail]] On Behalf Of Adrian Farrel
> Sent: Monday, June 16, 2014 7:33 AM
> To: 'Dhruv Dhody'; 'Julien Meuric'
> Cc: [e-mail]
> Subject: Re: [Pce] PCEP ERO
> 
> Julien is right (of course).
> 
> This survey led (in part) to RFC 4990. section 6 may be what Dhruv is looking
for.
> 
> A nasty question lurking in the background is whether a PCC needs to indicate
> which construction of ERO is prefers. Consider if the interface was CLI not
> PCEP: in this case the supported construction of ERO is part of the CLI
definition.
> However, given that most of the ERO is not for local consumption and does not
> need to be examined by the PCC, this question may be of debatable value.
> 
> Adrian
> 
> > -----Original Message-----
> > From: Pce [mailto:[e-mail]] On Behalf Of Dhruv Dhody
> > Sent: 16 June 2014 10:27
> > To: Julien Meuric
> > Cc: [e-mail]
> > Subject: Re: [Pce] PCEP ERO
> >
> > Hi Julien,
> >
> > Thanks for the pointer, this surely helps.
> > Time to dive into the archives.....
> >
> > Dhruv
> >
> > On Mon, Jun 16, 2014 at 2:29 PM, Julien Meuric
> > <[e-mail]>
> > wrote:
> > > Hi Dhruv.
> > >
> > > PCEP does not mandates more rules on ERO than RSVP-TE, which reminds
> > > me
> > of
> > > an old discussion in CCAMP. You may want to have a look at
> > > http://tools.ietf.org/html/draft-farrel-ccamp-ero-survey-00 and dive
> > > into the associated thread back in 2006.
> > >
> > > Julien
> > >
> > >
> > > Jun. 16, 2014 - Dhruv Dhody:
> > >>
> > >> Attaching the figure in a pdf, in case you could not view in my
> > >> previous mail.
> > >>
> > >> Regards,
> > >>
> > >> Dhruv
> > >>
> > >> ---------------------------------------------------------------
> > >>
> > >> *Dhruv Dhody *
> > >>
> > >>
> > >> System Architect,
> > >>
> > >> Huawei Technologies India Pvt. Ltd.,
> > >>
> > >> Banagalore
> > >>
> > >> Mobile: [phone]
> > >>
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> > >>
> > >> *From:*Dhruv Dhody
> > >> *Sent:* 16 June 2014 11:52
> > >> *To:* [e-mail]
> > >> *Subject:* PCEP ERO
> > >>
> > >>
> > >> Dear WG,
> > >>
> > >>
> > >> Consider the below topology, PCE computes a path from RTA to RTC.
> > >>
> > >> This path maybe encoded in PCEP ERO as  -
> > >>
> > >> ~ (10.1.1.1, 10.1.1.2, 20.1.1.1, 20.1.1.2)
> > >>
> > >> or
> > >>
> > >> ~ (10.1.1.2, 20.1.1.1, 20.1.1.2) [without local IP address of
> > >> ingress]
> > >>
> > >> IMO both should be considered as viable options.
> > >>
> > >> Is there any reason for PCC to consider one of them as incorrect?
> > >>
> > >> Regards,
> > >>
> > >> Dhruv
> > >>
> > >> ---------------------------------------------------------------
> > >>
> > >> Dhruv Dhody
> > >>
> > >> System Architect,
> > >>
> > >> Huawei Technologies India Pvt. Ltd.,
> > >>
> > >> Banagalore
> > >>
> > >> Mobile: [phone]
> > >>
> > >>
> > >>
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