Hi Acee,

I think we do not need to agree on the philosophical question whether defining detour path by packet header instead of signaling states brings the feature out of TE...

Anyway we agree that consolidating information from 3 separates LSA is not the most efficient processing. My point is that this slight improvement does not balance the risk of inconsistent advertisements/configuration that the current I-D does not (even try to) prevent.

Regards,

Julien


Nov. 07, 2015 - [email protected]:
Hi Julien,

One such non-TE application where there is a clear advantage of
advertising these attributes is segment routing TI-LFA. In addition to all
the detriments of requiring advertisement of TE LSAs when TE is not
enabled, one would need to consolidate information for a link from 3
separate LSAs (the base Router-LSA, the prefix-list attribute LSA for the
adjacency SID, and the TE LSA). Clearly, it is better to advertise the
applicable attributes in the Prefix/Link Attribute LSA and reduce this
burden. You will note that this advantage isn’t apparent in IS-IS where
everything is advertised in one monolithic LSP.

Thanks,
Acee

On 11/5/15, 7:03 PM, "OSPF on behalf of Julien Meuric"
<[email protected] on behalf of [email protected]> wrote:

Hello Peter,

Nov. 05, 2015 - [email protected]:
Hi Julien,

On 11/5/15 09:12 , Julien Meuric wrote:
Hi Jeff,

Following the WG session yesterday, I'm glad to (lately) join the
thread. Please, see my comments below as [JM].


Oct. 26, 2015 - [email protected]:
Hi,
No hats

I'm familiar with at least 2 implementations which have this issue,
this draft solves real problem.

Regards,
Jeff

[JM] Then you may consider patching them to do parameter duplication on
the receiver side, not on the wire and/or the emitter configuration...
Do you imagine operational people tearing hair out while trying to
guess
if they need to configure SRLGs in here, there or both? All the more as
two places would multiply configuration discrepancies.

above is incorrect.
Nobody is proposing to configure things like SRLG on multiple places.
[JM] Actually you do in the I-D: "it is expected that the information
would be identical. If they are different..."

You configure it on a single place, as you do today. If IGP is enabled
for global SRLG protection, IGP pulls the SRLGs and advertise them in
the Extended Prefix LSA. If TE is enabled and want to use SRLGs, it
pulls it from the same place, form the TE Opaque LSA and asks IGP to
flood it.
[JM] This reads to me like "in case both types of LSAs are used, values
MUST be identical". This is very different from the loose text in your
I-D.



In the I-D, the beginning and the end of section 3.1 provide a good
summary:
- "One approach for advertising link attributes is to _continue_ to use
TE Opaque LSA"
- advantages: "no additional standardization requirement", "link
attributes are only advertised once".
I cannot agree more on these.

have you read the "disadvantage" section as well?
[JM] Of course not, since Shraddha already solved them in his original
e-mail. :-)


In other words, some new use cases, not matching the original one, do
not justify to allocate new code points to the same information (cf.
IS-IS non-issue). In the IETF, uses cases aim at scoping protocol work,
they aren't made to limit protocol future uses.

I;m afraid you are missing the point.
TE Opaquer LSA are defined as LSAs that advertise TE topology that is
disjoint from the IGP topology (RFC3630). We can NOT make the link part
of the TE topology, just because we want to advertise SRLG or some other
attribute that is used by IGP for LFA - that would break the RFC3630.
[JM] Indeed, I am missing the point where a link state protocol is
forbidden to access the link parameters it is distributing in its link
state advertisements. Please, point me to the section from RFC 3630 it
"breaks".


thanks,
Peter

[JM] You're welcome,

Julien


Cheers,

Julien

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