Re: [Pce] PCEP ERO

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

Good digging, Xian. Thanks.

That covers it better than my email (although the effect is the same :-)

Cheers,
Adrian

> -----Original Message-----
> From: Zhangxian (Xian) [mailto:[e-mail]]
> Sent: 17 June 2014 03:17
> 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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