Re: [bitcoin-dev] BIP proposal: NODE_NETWORK_LIMITED service bits

[Jonas Schnelli <dev@jonasschnelli.ch>]

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> Is 49 days particularly useful? Would it be a problem to instead leave both-
> bits undefined? I'm thinking this might be better as a way to indicate "7
> days, plus a deterministically chosen set of historical blocks"…

I though two service bits allow three states and we should define all three combinations.
But I guess an adequate „definition“ would be to reserve it for future „definitions“.
Or use Gregory's proposal of min 2016*2 blocks & keep it „undefined“ for now.

49 days was chosen to allow SPV peers to be „offline“ for a month and still be capable to catch-up with a peer pruned to a datadir of ~10GB.

> 
> This is technically true right now, but as soon as segwit activates, it will
> no longer be... Therefore, I suggest striking it from the BIP, expounding on
> it in greater detail, or making it true for the longer term.

AFAIK Core does also guaranteed the 288 blocks post segwit activation:
https://github.com/bitcoin/bitcoin/blob/08a7316c144f9f2516db8fa62400893f4358c5ae/src/validation.h#L204
But maybe I’m confused.

> 
>> Peers following this BIP SHOULD connect a limited amount of their available
>> outbound connections to peers signaling one or both of the
>> NODE_NETWORK_LIMITED_* service bits if they expect to request less blocks
>> than the signaled number.
> 
> This isn't entirely clear whether it refers to peers downloading blocks, or
> peers serving them. (I assume the former, but it should be clarified.)

Indeed. I’ll try to make that more clear.

> 
>> Light clients (and such) who are not checking the nServiceFlags (service
>> bits) from a relayed addr-message may unwillingly connect to a pruned peer
>> and ask for (filtered) blocks at a depth below their pruned depth.
> 
> Wouldn't this already be a problem, without the BIP?

AFAIK, Core does currently only relay NODE_NETWORK addresses.
But yes, It may be a problem already.

</jonas>


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