p2p: Add disabletx message

This message, valid between version/verack for peers with version >= 70017,
would allow establishing at the time of connection that no transactions will be
announced/requested between those peers.

Author: sdaftuar

bip-disable-tx.mediawiki

@@ -0,0 +1,100 @@
+<pre>
+  BIP: XXX
+  Layer: Peer Services
+  Title: Disable transaction relay message
+  Author: Suhas Daftuar <[email protected]>
+  Comments-Summary: No comments yet.
+  Comments-URI:
+  Status: Draft
+  Type: Standards Track
+  Created: 2020-09-03
+  License: BSD-2-Clause
+</pre>
+
+==Abstract==
+
+This BIP describes a change to the p2p protocol to allow a node to tell a peer
+that a connection will not be used for transaction relay, to support
+block-relay-only connections that are currently in use on the network.
+
+==Motivation==
+
+For nearly the past year, software has been deployed[1] which initiates
+connections on the Bitcoin network and sets the transaction relay field
+(introduced by BIP 37 and also defined in BIP 60) to false, to prevent
+transaction relay from occurring on the connection. Additionally, addr messages
+received from the peer are ignored by this software.
+
+The purpose of these connections is two-fold: by making additional
+low-bandwidth connections on which blocks can propagate, the robustness of a
+node to network partitioning attacks is strengthened.  Additionally, by not
+relaying transactions and ignoring received addresses, the ability of an
+adversary to learn the complete network graph (or a subgraph) is reduced[2],
+which in turn increases the cost or difficulty to an attacker seeking to carry
+out a network partitioning attack (when compared with having such knowledge).
+
+The low-bandwidth / minimal-resource nature of these connections is currently
+known only by the initiator of the connection; this is because the transaction
+relay field in the version message is not a permanent setting for the lifetime
+of the connection.  Consequently, a node receiving an inbound connection with
+transaction relay disabled cannot distinguish between a peer that will never
+enable transaction relay (as described in BIP 37) and one that will.  Moreover,
+the node also cannot determine that the incoming connection will ignore relayed
+addresses; with that knowledge a node would likely choose other peers to
+receive announced addresses instead.
+
+This proposal adds a new, optional message that a node can send a peer when
+initiating a connection to that peer, to indicate that connection should not be
+used for transaction-relay for the connection's lifetime. In addition, without
+a current mechanism to negotiate whether addresses should be relayed on a
+connection, this BIP suggests that address messages not be sent on links where
+tx-relay has been disabled.
+
+==Specification==
+
+# A new disabletx message is added, which is defined as an empty message where pchCommand == "disabletx".
+# The protocol version of nodes implementing this BIP must be set to 70017 or higher.
+# If a node sets the transaction relay field in the version message to a peer to false, then the disabletx message MAY also be sent in response to a version message from that peer if the peer's protocol version is >= 70017. If sent, the disabletx message MUST be sent prior to sending a verack.
+# A node that has sent or received a disabletx message to/from a peer MUST NOT send any of these messages to the peer:
+## inv messages for transactions
+## getdata messages for transactions
+## getdata messages for merkleblock (BIP 37)
+## filteradd/filterload/filterclear (BIP 37)
+## mempool (BIP 35)
+# It is RECOMMENDED that a node that has sent or received a disabletx message to/from a peer not send any of these messages to the peer:
+## addr/getaddr
+## addrv2 (BIP 155)
+# The behavior regarding sending or processing other message types is not specified by this BIP.
+# Nodes MAY decide to not remain connected to peers that send this message (for example, if trying to find a peer that will relay transactions).
+
+==Compatibility==
+
+Nodes with protocol version >= 70017 that do not implement this BIP, and nodes
+with protocol version < 70017, will continue to remain compatible with
+implementing software: transactions would not be relayed to peers sending the
+disabletx message (provided that BIP 37 or BIP 60 has been implemented), and while
+periodic address relay may still take place, software implementing this BIP
+should not be disconnecting such peers solely for that reason.
+
+Disabling address relay is suggested but not required by this BIP, to allow for
+future protocol extensions that might specify more carefully how address relay
+is to be negotiated. This BIP's recommendations for software to not relay
+addresses is intended to be interpreted as guidance in the absence of any such
+future protocol extension, to accommodate existing software behavior.
+
+Note that all messages specified in BIP 152, including blocktxn and
+getblocktxn, are permitted between peers that have sent/received a disabletx
+message, subject to the feature negotiation of BIP 152.
+
+==Implementation==
+
+TBD
+
+==References==
+
+# Bitcoin Core has [https://github.com/bitcoin/bitcoin/pull/15759 implemented this functionality] since version 0.19.0.1, released in November 2019.
+# For example, see https://www.cs.umd.edu/projects/coinscope/coinscope.pdf and https://arxiv.org/pdf/1812.00942.pdf.
+
+==Copyright==
+
+This BIP is licensed under the 2-clause BSD license.