On Thu, Oct 17, 2019 at 01:16:47PM -0700, Eric Voskuil via bitcoin-dev wrote:

As this is a P2P protocol change it should be exposed as a version

increment (and a BIP) [...]

BIP61 is explicit:

“All implementations of the P2P protocol version 70,002 and later

should support the reject message.“

I don't think a new BIP or a version number increment is necessary.

1. "Should support" isn't the same as "must support".  See
  https://tools.ietf.org/html/rfc2119 ; by that reading,
  implementations with protocol versions above 70,002 are not required
  to support the reject message.

2. If you don't implement a BIP, as Bitcoin Core explicitly doesn't any
  more for BIP61[1], you're not bound by its conditions.

-Dave

[1] https://github.com/bitcoin/bitcoin/blob/master/doc/bips.md  "BIP61
[...] Support was removed in v0.20.0"