To be more precise, my question is not to know if the AS number
sub TLV is useful cause I agree that it is.
But rather is it madatory to encode such sub TLV in each inter
domain TE link.
There are some scenario where it is useful (e.g. PCE based path
computation), maybe it is not in some other scenarios.
For instance RFC3630 states that " The Link Type and Link ID
sub-TLVs are mandatory, i.e., must appear exactly once", and
I think the same kind statement should be done to explicitly
indicate if the AS number sub TLV is mandatory or optional
in case of inter domain TE link.
Yes, we will make such statement in the next revision.
As to mandatory or optional, although the AS number attribute of
an inter-AS TE links is very useful for many computation scenarios,
but only if there is one scenario that does not need the AS number
attribute, the AS number sub-TLV should not be mandatory, so
optional is more reasonable for the AS number sub-TLV.
I think quite the oposite!
If there is one scenario where the information is required then
advertisement is mandatory. Consider that the advertising router does not
know to what use the information will be put. Therefore, you cannot allow
the advertising router to make an arbitrary decision about what information
to advertise - that would potentially make the advertisement useless.
The only reason that you would make this less than a MUST, would be if you
find policy reasons why the AS number might be withheld.
Since there is no OSPF adjancy runing on the inter-AS TE
links, to advertise both directions of the TE link can
make sure that the inter-AS TE link is valid for path
computation. As Vishwas Manral said, CSPF implementations
will do a two way check before using the TE link for path
computation.
Ok. But then if the only purpose of having 2 links LSA is
to be able to do 2 way connectivity check, why not rather
stating that the inter domain TE link is bidirectional
(unlike intra domain link).
That is, this TE link would be advertised only if the
advertising routers has checked the 2-way connectivity.
A bidirectional inter-AS link is an option. But, IMO,
from the aspect of implementing (especially CSPF), using
2 link LSAs as current intra-area TE does is simpler than
using a new bidirectional inter-AS LSA.
Right. We don;t want to force changes to core code (such as CSPF) for this
new function.
Adrian
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