In Downstream Unsolicited label advertisement mode, Ru does
not know what Ruu wants or needs. Ru always propagates the FEC upstream
and Ruu uses it if needed.
So once some node decides to do this "LDP de-summarization", there's no way
to stop it until you reach the border of the MPLS domain? I think we'd
probably end up with a bunch of configuration knobs controlling LDP
desummarization, similar to the knobs controlling IGP summarization.
there is no change compared to using RFC 3036 and performing route leaking
on ABR. In both cases, in the FIB, you have an aggregated prefix and more
specific ones.
I didn't say that your proposal adds more prefixes to the FIB than it would
have if the the /32s were carried by OSPF. I said that the management of
the forwarding table is made more complicated, because we now have entries
which are jointly managed by two different protocols which have a complex
relationship with each other.
instead of advertising the specific prefixes once in the IGP and once in
the LDP, we would only advertise it once
I don't think this is a meaningful comparison. LDP does not currently
advertise prefixes, it advertises label bindings. In your proposal, new
functionality is added so that LDP does advertise prefixes. Thus the number
of "prefix advertisements" stays the same. You're merely shifting some of
the prefix advertisement burden from one protocol to the other. And the
work of managing those prefixes in the forwarding table is more
complicated. All that really gets saved is the work required to parse the
OSPF messages.
I guess my problem is that I see the additional complexity, but I don't see
the data showing that, as a result of adding this complexity, we gain a big
improvement in the number of /32s to which we can assign labels. I also
don't see that this is yields a better set of tradeoffs than a hierarchical
soltuion.
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