The MPLS WG Archive

[Jean Philippe Vasseur <jvasseur@cisco.com>]

Hi Dimitri,

Thanks for your useful comments here. See below,

At 02:18 PM 3/30/2004 +0200, Dimitri.Papadimitriou@alcatel.be wrote:
>hi jl, here below several comments on this updated version of the document:
>
>1) section 5.3.1 mentions:
>
>"The solution MUST entirely preserve the concept of IGP hierarchy. In
>    other words, flooding of TE link information across areas MUST be
>    precluded."
>
>section 5.3.2 mentions:
>
>"The solution MUST also not increase IGP load which could compromise
>    IGP scalability. In particular, a solution satisfying those
>    requirements MUST not require for the IGP to carry some unreasonable
>    amount of extra information and MUST not unreasonably increase the
>    IGP flooding frequency."
>
>but section 7.12 tells:
>
>"The discovery mechanism SHOULD
>    be applicable across multiple IGP areas, and SHOULD not impact the
>    IGP scalability, provided that IGP extensions are used for such a
>    discovery mechanism."
>
>-> would it be possible to align these requirements, i get the impression 
>(please confirm) that you preclude TE link information but you would allow 
>for node information (auto-mesh) ? note also that the section 7.12 doesn't 
>tell us a lot about the expected distribution of the mesh

The solution MUST preclude to flood TE-related link information and MUST 
not compromise the IGP scalability in any circumstances. That being said, 
IGP based mechanisms can be used for the discovery which will respect the 
requirement mentioned above,

>2) section 7.3
>
>"   In the context of this requirement document, an optimal path is
>    defined as the shortest path across multiple areas taking into
>    account either the IGP or TE metric. "
>
>are you referring here to
><http://www.ietf.org/internet-drafts/draft-ietf-tewg-te-metric-igp-02.txt>
>
>would you clarify ?

Sure, we will add some text. The reason for this clarification is that 
there are a multitude of definitions for an optimal path: paths that 
minimize the max link utilization, call set up failure, ... here we just 
refer to the ability to compute a shortest path (using either the IGP or TE 
metric).


>3) section 7.3
>
>it is not clear for me what is behind the last part of the following sentence
>
>"So a solution should support both mechanisms, and SHOULD allow
>    the operator to select by configuration, and on a per-LSP basis, the
>    required level of optimality. "
>
>what is meant by "level of optimality" ? is it simply "optimal - 
>sub-optimal" or do you have something else in mind ?

We will clarify. The idea is that the ability to compute an end to end 
shortest path may not be required for all inter-area TE LSPs. Hence the 
solution should allow the operator to select the appropriate path 
computation method.

>4) section 7.4
>
>"Another example is the requirement to set up multiple TE LSPs between
>    a pair of LSRs residing in different IGP areas in case a single TE
>    LSP satisfying the set of requirements could not be found. "
>
>why in such a case diversity would be desirable ?

for either path protection or load balancing while minimizing the impact in 
case of failure.

>got the impression that if a single path would have been feasible it would 
>have been selected in this case - isn't it ?

That being said, we need to rephrase, I agree with you that this paragraph 
is not clear. It should read:

"Another example is the requirement to set up multiple TE LSPs between a 
pair of LSRs residing in different IGP areas. For instance, this would 
occur if TE LSP satisfying for instance the bandwidth requirement could be 
found, hence, requiring to set up multiple TE LSPs"

>5) section 7.7
>
>"This may reduce the recovery delay, but with the risk of
>    multiple crankbacks, and sub-optimality.  "
>
>i agree, but this is valid iff the head-end has initially computed an 
>end-to-end optimal path,

more exactly this applies to contiguous LSP. For sub-optimality this 
applies to any kind of LSP.

>also unclear if you refer also here to the provisioning delay ?
>
>editorially speaking it is also a bit unclear why you've splitted section 
>7.7 and section 7.8 both refers to inter-area lsp recovery
>
>6) section 7.11
>
>would it be possible to mention what's expected (or not expected) in terms 
>also of hard preemption ?

ok


>7) section 8.2
>
>what's meant by stability ? ie stability of what ? (for instance, as i 
>read the document, but please correct me, stability and re-optimization 
>are imho two features that are going in somehow opposite directions so a 
>trade-off has to be found here)

We will clarify.

thanks for your comments !

JP.

>thanks in advance,
>- dimitri.
>
>LE ROUX Jean-Louis FTRD/DAC/LAN wrote:
>
>>Hi all,
>>Thanks in advance for your comments on this new revision of inter-area
>>TE requirements.
>>Regards,
>>JL
>>
>>>A New Internet-Draft is available from the on-line Internet-Drafts 
>>>directories. This draft is a work item of the Internet Traffic 
>>>Engineering Working Group of the IETF.
>>>
>>>        Title           : Requirements for Inter-area MPLS Traffic
>>Engineering
>>
>>>        Author(s)       : J. Le Roux, et al.
>>>        Filename        : draft-ietf-tewg-interarea-mpls-te-req-00.txt
>>>        Pages           : 20
>>>        Date            : 2004-3-26
>>>
>>>This document lists a detailed set of functional requirements for the
>>>support of inter-area MPLS Traffic Engineering (inter-area MPLS TE) 
>>>which could serve as a guideline to develop the required set of protocol 
>>>extensions.
>>>
>>>A URL for this Internet-Draft is:
>>>http://www.ietf.org/internet-drafts/draft-ietf-tewg-interarea-mpls-te-r
>>eq-00.txt
>>
>>>To remove yourself from the IETF Announcement list, send a message to
>>>ietf-announce-request with the word unsubscribe in the body of the message.
>>>
>>>Internet-Drafts are also available by anonymous FTP. Login with the
>>>username "anonymous" and a password of your e-mail address. After 
>>>logging in, type "cd internet-drafts" and then
>>>        "get draft-ietf-tewg-interarea-mpls-te-req-00.txt".
>>>
>>>A list of Internet-Drafts directories can be found in
>>>http://www.ietf.org/shadow.html or ftp://ftp.ietf.org/ietf/1shadow-sites.txt
>>
>
>--
>Papadimitriou Dimitri
>E-mail : dimitri.papadimitriou@alcatel.be
>E-mail : dpapadimitriou@psg.com
>Webpage: http://psg.com/~dpapadimitriou/
>Address: Fr. Wellesplein 1, B-2018 Antwerpen, Belgium
>Phone  : +32 3 240-8491
>
>