Re: [Lsr] Dynamic flow control for flooding

["Les Ginsberg (ginsberg)" <[e-mail]>]

Tony –

As usual, you cover a lot of territory – and even after a couple of readings I am not sure I got everything.
Still, I dare to reply.
Inline.

From: Tony Przygienda <[e-mail]>
Sent: Tuesday, July 23, 2019 1:56 PM
To: Les Ginsberg (ginsberg) <[e-mail]>
Cc: Tony Li <[e-mail]>; [e-mail]
Subject: Re: [Lsr] Dynamic flow control for flooding



It is a mistake to equate LSP flooding with a set of independent P2P “connections” – each of which can operate at a rate independent of the other.



At least my experience much disagrees with that and such a proposal seems to steer towards slowest receiver in the whole network problem so I wait for others to chime in.
[Les:] This is NOT AT ALL where I am going.
If I have a “large network” and I have a node which consistently cannot support the flooding rates necessary to deal with Tony Li’s example (node w many neighbors fails) then the network has a problem.
Slowing down everyone to meet the flooding speed of the slowest speed is not something I would expect a customer to accept. The network will not be able to deliver the convergence expected. The node in question needs to be identified and steps taken to either fix it or upgrade or replace it or…

The point I am also making is trying to run the network with some links flooding fast and some links flooding slow isn’t a solution either.

Then, to clarify on Tony's mail, the "problem" I mentioned anecdotally yesterday as behavior I saw on things I did in their time was of course when processors were still well under 1GHz and links in Gigs and not 10s and 100s of Gigs we have today but yes, the limiting factor was the flooding rate (or rather effective processing rate of receiver AFAIR before it started drop the RX queues or was late enough to cause RE-TX on senders) in terms of losses/retransmissions necessary that were causing transients to the point it looked to me then the cure seemed worse than the disease (while the disease was likely a flu then compared to today given we didn't have massively dense meshes we steer towards today). The base spec & mandated flooding numbers didn't change but what is possible in terms of rates when breaking the spec did change of course in terms of CPU/links speed albeit most ISIS implementations go back to megahertz processors still ;-) And the dinner was great BTW ;-)

So yes, I do think that anything that will flood @ reasonable rate without excessive losses will work well on well-computed double-flood-reduced-graph, the question is how to get the "reasonable" in place both in terms of numbers as well as mechanism for which we saw tons lively discussions/proposal yesterday, most obvious being of course going and manually bumping e'one's implementation to the desired (? ;-) value ...  Other consideration is having computation always trying to get more than 2 links in minimal cut on the graph of course which should alleviate any bottleneck or rather, make the cut less likely. Given quality of max-disjoint-node/link graph computation algorithms that should be doable by gut feeling. If e.g. the flood rate per link is available the algorithms should be doing even better in centralized case.

[Les:] Convergence issues and flooding overload as a result of excessive redundant flooding is a real issue – but it is a different problem (for which we have solutions) and we should not introduce that issue into this discussion.

   Les

BTW, with all that experience (MANET did its share in different space as we know in terms of flood reduction as well) in RIFT we chose a solution based on MANET derivative where every source chooses a different set of trees to flood on using Fisher-Yates hashes but that seems possible only if you have directionality on the graph (that's what I said once on the mike that doing flood reduction in a lattice [partial rank-ordered graph with upper & lower bounds] is fairly trivial, on generic graphs not so much necessarily). But maybe Pascal reads that and gives it a think ;-)

as usual, 2 cents to improve the internet ;-)

--- tony