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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