Hi Chris,
please see inline:
On 10/22/15 17:00 , Chris Bowers wrote:
Peter,
I would suggest making the text of the draft more explicit about the conditions
under which a given link and set of attributes should be included in the TE
Opaque LSA or the Extended Link Opaque LSA. RFC3630 is subject to
interpretation on its own, and since it was written before the existence of the
Extended Link Opaque LSA, it is not self-evident how to interpret it with
respect to using this new LSA. Clarifying the proposed rules for use of the
TE Opaque LSA or the Extended Link Opaque LSA without relying on
interpretations of 3630 will be helpful. It will help the WG evaluate the
proposal overall and determine what, if any, backwards compatibility issues
this proposal may cause with existing implementations. It may also help future
implementers avoid interoperability and backwards compatibility issues.
Sure, we can add more text in the draft.
What I have a problem with is that you are questioning RFC3630 and claim
that it subject to interpretation. I don't think that is the case.
RFC3630 defines TE Opaque LSAs as a mechanism to describe TE topology.
There is nothing left that is subject to interpretation. If we do not
have an agreement on this part, there is no text in the draft that is
going to make things clear.
As a concrete example, I think it would be useful to explicitly address the
case of how to advertise a link that only supports LDP in the text of the
draft. Below is an example of a format that would clarify this. From the
response to my question below regarding LDP, I assume that a link that only
supports LDP signaling and not RSVP-signaling would not be advertised in the TE
Opaque LSA. However, I am honestly not positive that this is what is intended.
LDP being enabled on link is orthogonal to link being part of the TE
topology. Implementation can choose what makes link part of TE topology,
some may have explicit command on a per interface basis, some may do it
based on some other feature being enabled on the link. No matter what
mechanism they use it is a local decision on the box that makes the link
part of TE topology and triggers the advertisement of the TE Opaque LSA
for such link. What is important is that as soon as the TE Opaque LSA is
flooded all other nodes in the area will assume they can use such link
for traffic engineering and use it during the TE cSPF.
Format of proposed clarifying text:
------------------
A link MUST NOT be advertised in the TE Opaque LSA under the following
conditions:
1) The link does not support RSVP-TE signaling.
one can do traffic engineering without RSVP. RFC3630 does not mandate
the usage of RSVP.
2) Another condition...
A link MAY be advertised in the TE Opaque LSA under the following conditions:
the only condition is that user decided to make the link part of the
traffic engineering topology, regardless of what is the local mechanism
on the box to make that happen.
1) Another condition ...
A link MUST NOT be advertised in the Extended Link Opaque LSA under the
following conditions:
I do not see any reason to specify why a link MUST NOT be advertised in
Extended Link Opaque LSA.
TE Opaque LSA and Extended Link Opaque LSA are orthogonal to each other.
TE Opaque LSA is dedicated for traffic engineering and must not be used
for anything else.
thanks,
Peter
1) Some other condition ....
Thanks,
Chris
-----Original Message-----
From: Peter Psenak [mailto:[email protected]]
Sent: Wednesday, October 21, 2015 3:24 PM
To: Chris Bowers <[email protected]>; Acee Lindem (acee) <[email protected]>; Shraddha Hegde
<[email protected]>; OSPF WG List <[email protected]>
Subject: Re: [OSPF] Regarding draft-ppsenak-ospf-te-link-attr-reuse-00
Hi Chris,
On 10/21/15 21:44 , Chris Bowers wrote:
Peter,
RFC3630 does not appear to restrict the use of the attributes it defines. The term "TE
extensions" may seem to imply some restriction, but the Applicability section of RFC3630
explicitly addresses this potential interpretation by saying that a more accurate designation is
"extended link attributes".
1.1. Applicability
Many of the extensions specified in this document are in response to
the requirements stated in [5], and thus are referred to as "traffic
engineering extensions", and are also commonly associated with MPLS
Traffic Engineering. A more accurate (albeit bland) designation is
"extended link attributes", as the proposal is to simply add more
attributes to links in OSPF advertisements.
RFC3630 says:
The extensions provide a way of describing the traffic engineering
topology (including bandwidth and administrative constraints) and
distributing this information within a given OSPF area. This
topology does not necessarily match the regular routed topology,
above clearly indicates that if the link is advertised in TE Opaque LSA, it is
part of the TE topology, otherwise it is not. That restricts the usage of the
TE Opaque LSA to the links that are part of the TE topology.
-------
Also, the response below uses the term "TE-enabled" which along with "TE-application" does not
appear to have a precise definition in draft-ppsenak-ospf-te-link-attr-reuse-00. Based on RFC 3630, it seems
reasonable to say that a link is "TE-enabled" if the link is advertised in the TE Opaque LSA. I don't think
this is the meaning you intend, so to avoid confusion, I will use the term "RFC-3630-TE-enabled" to mean that
the link is advertised in the TE Opaque LSA defined in RFC 3630.
So can you clarify what "TE-enabled" or a "TE-application" means in your document? I
assume that it should mean that MPLS is enabled, but it is actually not clear to me if just having
LDP-enabled on a link would qualify as being "TE-enabled" or not.
TE-enabled means the link is part of the traffic engineering topology as
described by RFC3630.
thanks,
Peter
Thanks,
Chris
-----Original Message-----
From: Peter Psenak [mailto:[email protected]]
Sent: Wednesday, October 21, 2015 12:40 PM
To: Chris Bowers <[email protected]>; Acee Lindem (acee) <[email protected]>; Shraddha Hegde
<[email protected]>; OSPF WG List <[email protected]>
Subject: Re: [OSPF] Regarding draft-ppsenak-ospf-te-link-attr-reuse-00
Hi Chris,
On 10/21/15 19:20 , Chris Bowers wrote:
In my opinion the backwards compatibility problems introduced by this
proposal outweigh potential gains.
there is no backwards compatibility problem with the draft.
As a concrete example, there is at least one existing implementation
of remote LFA where policy is used to select a backup tunnel that does
not share an SRLG with the failed link. This SRLG information is
carried in the TE Opaque LSA.
that is fine, you are free to do that if the link is TE enabled, there is no
problem. If the link is not TE enabled and you use TE Opaque LSA to flood the
SRLG data for such link, you are going against the current specification. There
is no way to do that today, because any router that would receive such TE
Opaque LSA must assume such link is TE enabled.
As it currently reads, I think the proposal in
draft-ppsenak-ospf-te-link-attr-reuse has the potential to break
existing standards-compliant implementations.
I don't believe so.
I might be OK with having the proposal only apply to sub-TLVs that
get defined in the future. However, I think that taking TLVs that were
standardized over ten years ago, and selectively moving them or
copying them to a different LSA based on a set of rules that is
subject to interpretation is going to create confusion and
interoperability headaches.
What we propose is the way to advertise link attributes without making the link
part of TE topology. We simply do not have a way to do that today. I do not see
any problem in doing so, because we do not change anything on the TE Opaque LSA
side, we are defining something new.
thanks,
Peter
Chris
*From:*OSPF [mailto:[email protected]] *On Behalf Of *Acee Lindem
(acee)
*Sent:* Wednesday, October 21, 2015 6:48 AM
*To:* Shraddha Hegde <[email protected]>; OSPF WG List
<[email protected]>
*Subject:* Re: [OSPF] Regarding
draft-ppsenak-ospf-te-link-attr-reuse-00
Hi Shraddha,
*From: *OSPF <[email protected] <mailto:[email protected]>> on
behalf of Shraddha Hegde <[email protected]
<mailto:[email protected]>>
*Date: *Wednesday, October 21, 2015 at 1:20 AM
*To: *OSPF WG List <[email protected] <mailto:[email protected]>>
*Subject: *[OSPF] Regarding draft-ppsenak-ospf-te-link-attr-reuse-00
Hi All,
draft-ppsenak-ospf-te-link-attr-reuse-00 proposes moving and/or
copying TLVs from the TE Opaque LSA to the Extended Link Opaque LSA.
The draft lists the problems that the draft is trying to solve. I
have reproduced that list of problems below, with each problem
followed by what I believe to be a better and simpler solution.
1. Whenever the link is advertised in a TE Opaque LSA, the
link
becomes a part of the TE topology, which may not match IP
routed
topology. By making the link part of the TE topology,
remote
nodes may mistakenly believe that the link is available
for MPLS
TE or GMPLS, when, in fact, MPLS is not enabled on the link.
To address this issue, we simply need to define a new sub-TLV in the
TE Link LSAto say whether MPLS/GMPLS/RSVP is enabled on the link
instead of moving the TLVs around into different LSAs.
2. The TE Opaque LSA carries link attributes that are not
used or
required by MPLS TE or GMPLS. There is no mechanism in TE
Opaque
LSA to indicate which of the link attributes should be
passed to
MPLS TE application and which should be used by OSPFv2 and
other
applications.
OSPF database is a container and OSPF can use any of the LSAS for
its own use including the TE LSAs.As far as the TE database goes, it
contains data from TE LSAs as well as non-TE LSAs (Network LSA)
today so thereasoning described here doesn't make sense.
3. Link attributes used for non-TE purposes is partitioned
across
multiple LSAs - the TE Opaque LSA and the Extended Link
Opaque
LSA. This partitioning will require implementations to
lookup
multiple LSAs to extract link attributes for a single
link,
bringing needless complexity to the OSPFv2 implementations.
There will be nodes in the network which will run older software
which send these attributes via TE LSAs so the problem of looking
into the TE LSAs for TE relatedinformation doesn't get solved with
this draft. Rather it makes it more complicated. With this draft,
the multiple LSA lookup will only increase.An implementation will
first have to find if Extended link LSA contains the required info,
if not it will need to lookup the info in TE.LSA.
The applications using the TE parameters for non-TE use-cases will use
the OSPF Prefix/Link attributes for these use cases. Hence, there is
no requirement to lookup the LSAs in multiple places. Backward
compatibility will be covered in the specifications of these applications.
Thanks,
Acee
Looking up multiple LSAs for information is an implementation issue
and I am sure there will be implementations that will handle this
gracefully so that it doesn't cause
delays in critical paths. It doesn't seem reasonable to come up with
protocol extensions to solve implementation issues.
Rgds
Shraddha
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