Date: Mon, 22 Feb 2021 20:16:32 +1000
From: Anthony Towns <aj@erisian.com.au>
To: Matt Corallo <lf-lists@mattcorallo.com>
Message-ID: <20210222101632.j5udrgtj2aj5bw6q@erisian.com.au>
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 <4FF38E1A-677B-478C-B32F-4640DF867810@mattcorallo.com>
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Cc: Michael Folkson <michaelfolkson@gmail.com>,
 Bitcoin Protocol Discussion <bitcoin-dev@lists.linuxfoundation.org>
Subject: Re: [bitcoin-dev] Yesterday's Taproot activation meeting on
 lockinontimeout (LOT)
Precedence: list

On Mon, Feb 22, 2021 at 01:44:55AM -0500, Matt Corallo wrote:
> A node feeding you invalid headers (used to be) cause for a ban [...]

Headers that are invalid due to MUST_SIGNAL rules are marked as
BLOCK_RECENT_CONSENSUS_CHANGE so don't directly result in a ban. If you're
doing headers-first relay, I think that will also prevent hitting the
BLOCK_MISSING_PREV case, which would result in a ban.

If a lockinontimeout=true node is requesting compact blocks from a
lockinontimeout=false node during a chainsplit in the MUST_SIGNAL phase,
I think that could result in a ban.

> More importantly, nodes on both sides of the fork need to find each other. 

(If there was going to be an ongoing fork there'd be bigger things to
worry about...)

I think the important specific case of this is something like "if a chain
where taproot is impossible to activate is temporarily the most work,
miners with lockinontimeout=true need to be well connected so they don't
end up competing with each other while they're catching back up".

Actually, that same requirement might be more practically for a signet
feature we were thinking about -- namely having "optional reorgs", ie
every now and then we'd mine 1-6 blocks and then reorg them out; but
also flag the soon-to-be-stale blocks in some way so that if you didn't
want to have to deal with reorgs you could easily ignore them. Having
it be possible for the "I want to see reorgs!" nodes to be able to find
each other seems like it might be a similar problem (avoiding having the
"don't-want-reorgs" nodes ban the "want-reorgs" nodes too perhaps).

Cheers,
aj