Hi Acee,
On 12/10/2021 21:05, Acee Lindem (acee) wrote:
Speaking as WG Chairs:
The authors of “Prefix Unreachable Announcement” have requested an
adoption. The crux of the draft is to signal unreachability of a prefix
across OSPF or IS-IS areas when area summarization is employed and
prefix is summarised. We also have “IS-IS and OSPF Extension for Event
Notification” which can be used to address the same use case. The drafts
take radically different approaches to the problem and the authors of
both drafts do not wish to converge on the other draft’s method so it is
understandable that merging the drafts really isn’t an option.
just for the record, I offered authors of "Prefix Unreachable
Announcement" co-authorship on "Event notification" draft, arguing the
the event base solution addresses their use case in a more elegant and
scalable way. They decided to push their idea regardless.
Before an adoption call for either draft, I’d like to ask the WG:
1. Is this a problem that needs to be solved in the IGPs? The use case
offered in both drafts is signaling unreachability of a BGP peer.
Could this better solved with a different mechanism (e.g., BFD)
rather than flooding this negative reachability information across
the entire IGP domain?
we have looked at the various options. None of the existing ones would
fit the large scale deployment with summarization in place. Using BFD
end to end to track reachability between PEs simply does not scale.
Some people believe this should be solved by BGP, but it is important to
realize that while the problem statement at the moment is primarily
targeted for egress PE reachability loss detection for BGP, the
mechanism proposed is generic enough and can be used to track the peer
reachablity loss for other cases (e.g GRE endpoint, etc) that do not
involve BGP.
We went even further and explored the option to use completely out of
band mechanism that do not involve any existing protocols.
Simply, the advantage of using IGP is that it follows the existing MPLS
model, where the endpoint reachability is provided by IGPs. Operators
are familiar with IGPs and know how to operate them.
On top of the above, IGP event notification can find other use cases in
the future, the mechanism defined in draft is generic enough.
2. Assuming we do want to take on negative advertisement in the IGP,
what are the technical merits and/or detriments of the two approaches?
we have listed some requirements at:
https://datatracker.ietf.org/doc/html/draft-ppsenak-lsr-igp-event-notification-00#section-3
From my perspective the solution should be optimal in terms of amount
of data and state that needs to be maintained, ideally separated from
the traditional LS data. I also believe that having a generic mechanism
to distribute events has it own merits.
thanks,
Peter
We’ll reserve any further discussion to “WG member” comments on the two
approaches.
Thanks,
Acee and Chris
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