Hi, Tony:
I am curious why you are so anxious to claim other solution, or make the
baseless ranking? Please do not misled the reader any more. It's not helpful
for the others to find the truth.
When the receivers receives the PUA information, the SPF algorithm will not be
triggered, then where is coming from what you claimed stress? They are just
messages, similar with your message that via other out-of-band channel.
Other responses inline.
Best Regards
Aijun Wang
China Telecom
-----Original Message-----
From: [email protected] <[email protected]> On Behalf Of Tony Li
Sent: Tuesday, January 25, 2022 3:25 PM
To: Aijun Wang <[email protected]>
Cc: Les Ginsberg (ginsberg) <[email protected]>; Gyan Mishra
<[email protected]>; Peter Psenak <[email protected]>;
Christian Hopps <[email protected]>; Robert Raszuk <[email protected]>; lsr
<[email protected]>
Subject: Re: [Lsr] BGP vs PUA/PULSE
Hi Aijun,
1) Consider in the BGP scenario: every PE may receive the routes from other
PEs, right? So, using the PUB/SUB model, every PE should subscribe the status
of the other PEs, right?
My understanding is that a PE typically only has tunnels to some other select
number of PEs. Yes, each PE would register for the other PEs that it connects
to.
[WAJ] No tunnel. You misunderstand the sentence, please read it again.
2) Consider in the tunnel scenario: every PE/P may select other PE/P as the
tunnel endpoint, right?, So, using the PUB/SUB model, every P/PE should
subscribe the status of other P/PEs, right?
Then, with the approach of PUB/SUB direction, the network will eventually
evolved into full mesh like subscription. That is, every device in the network
will care about every other device's status. Then, isn't the flooding mechanism
the most efficient one?
Efficient in what metric? In terms of the number of unique messages initiated,
yes. However, that is not the metric that matters. What matters is the load on
the network when there are failures and PUA dumps things into the L2 LSDB.
[WAJ] They are just messages. It's certainly no more than your out-of-band
messages.
We specifically have to design routing protocols to operate in worst case
scenarios. PUA means that there is no real upper bound to the worst case. Bad
news that we weren’t expecting can just keep piling up. The worst scale point
is when everything has failed. For ensuring stability that’s disasterous. And
stability is way, way, way more important than efficiency.
[WAJ] There is control method at the ABR, why you always ignores it? It like
that you do the summary work at ABR.
If we take the no summary solution, for the above so called "important
prefixes", then:
1) All the devices within the network will be filled with these detail prefixes
in the normal state, right?
Yes.
2) When there is the massive failure as that you often worried, the status of
such detailed prefixes will influence the IGP convergence, right?
Unlikely. If there are massive failures then prefixes will be withdrawn, not
added. State goes down. The stress on the network goes down. This is a highly
desirable property. Withdrawing state is not going to significantly affect the
performance of the IGP. SPF performance is O(n log n) for n = (# edges +
#nodes). The number of prefixes is relatively noise.
[WAJ] If your above explanation is right, it is the same for PUA solution.
Isn't it?
3) And, when the massive failure recovery, the status of such detailed prefixes
will influence AGAIN the performance of IGP, right?
No. Same reasoning.
[WAJ] Are you sure? State goes up, the stress on the network goes down?
But with the summary+PUA/PULSE(with the threshold control on ABRs as described
in https://mailarchive.ietf.org/arch/msg/lsr/fnP1dwvWhT3oRduwXGK73NzQAUo/),
1) There is NO stress for all the devices in the network to keep the above detailed
"important prefixes" in the normal state, right?
True. Also irrelevant.
[WAJ] You can always ignores the merits of other solutions.
2) There is CONTROLLED influence to the IGP when massive failure occur, right?
Perhaps, but the grave concern is that the ‘controlled influence’ is adequate
to maintain stability and yet providing some benefit. Again, the feature is
architected backwards: it adds stress under failure conditions. Exactly what we
don’t want.
And whatever control is installed, some customer will dial it up to 11 and then
call my CEO when their network melts down. No thank you.
[WAJ] Again, no SPF stress under failure condition. No more message than your
out-of-band solution.
3) There is NO influence to the IGP performance when massive failure recovery,
right?
Irrelevant. The recovery time is irrelevant. Again, the primary requirement is
stabiilty.
[WAJ] Very curious, how to get such conclusion?
Which one is the best option then?
As we’ve been saying for months now, the ordering is:
1) Leak PE loopbacks
2) Pub/Sub
3) Carry loopbacks in BGP and recurse
4) Multi-hop BFD
5) Pulse
6) PUA
Stability, stability, stability, and stability. Get the message?
[WAJ] From the above ranking, I begin again to doubt your expert's
undestanding. Please notice again when the router receives PUA message, no SPF
algorithm needed, Understand? Understand? Understand?
Tony
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