Hi, all
To make the node that is not TE enabled advertises link attributes for other
applications, it is worth considering another choice which has least change to
the protocol and implementation. The method is: advertising RI capability TLV
in RI LSA when advertising TE LSA. TE capability bit in RI capability TLV can
indicate whether link attributes should become part of TE topology.
In draft-ietf-ospf-rfc4970bis,
”an OSPF router advertising an OSPF RI LSA MAY include the Router
Informational Capability TLV’’ can be enhanced with: an OSPF router advertising
an OSPF RI LSA should include Router Informational Capability TLV which can
inform TE capability bit.
In this case, some improvement needs to be done in draft-ietf-ospf-rfc4970bis.
These are my personal view.
Best regards,
Ling XU
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
LSA to 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 the reasoning 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
related information 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 look up the info in TE.LSA.
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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