From c02ff3e793d6e781c6060d9d981bf71ae42fc17e Mon Sep 17 00:00:00 2001
From: Martin Zumsande <mzumsande@gmail.com>
Date: Tue, 21 Jul 2026 18:32:19 +0200
Subject: [PATCH] p2p: Assume v2transport for addresses from seeds

By now, the vast majority of nodes in the network supports BIP324.
Even if the optimistic guess would turn out to be wrong for a given
node, we would just reconnect with v1.
This is better than making v1 connections with peers when both nodes support v2.

Github-Pull: #35766
Rebased-From: cf0f2aeae009c98615bffd4dafd74e46f20a0ae6
---
 src/net.cpp    | 4 ++--
 src/protocol.h | 8 ++++++++
 2 files changed, 10 insertions(+), 2 deletions(-)

diff --git a/src/net.cpp b/src/net.cpp
index 5c28efade89..0afef682736 100644
--- a/src/net.cpp
+++ b/src/net.cpp
@@ -205,7 +205,7 @@ static std::vector<CAddress> ConvertSeeds(const std::vector<uint8_t> &vSeedsIn)
     while (!s.empty()) {
         CService endpoint;
         s >> endpoint;
-        CAddress addr{endpoint, SeedsServiceFlags()};
+        CAddress addr{endpoint, SeedsAssumedServiceFlags()};
         addr.nTime = rng.rand_uniform_delay(Now<NodeSeconds>() - one_week, -one_week);
         LogDebug(BCLog::NET, "Added hardcoded seed: %s\n", addr.ToStringAddrPort());
         vSeedsOut.push_back(addr);
@@ -2382,7 +2382,7 @@ void CConnman::ThreadDNSAddressSeed()
                 const auto addresses{LookupHost(host, nMaxIPs, true)};
                 if (!addresses.empty()) {
                     for (const CNetAddr& ip : addresses) {
-                        CAddress addr = CAddress(CService(ip, m_params.GetDefaultPort()), requiredServiceBits);
+                        CAddress addr = CAddress(CService(ip, m_params.GetDefaultPort()), SeedsAssumedServiceFlags());
                         addr.nTime = rng.rand_uniform_delay(Now<NodeSeconds>() - 3 * 24h, -4 * 24h); // use a random age between 3 and 7 days old
                         vAdd.push_back(addr);
                         found++;
diff --git a/src/protocol.h b/src/protocol.h
index 8ed90dd3f8e..00d046a02c0 100644
--- a/src/protocol.h
+++ b/src/protocol.h
@@ -353,6 +353,14 @@ std::vector<std::string> serviceFlagsToStr(uint64_t flags);
  */
 constexpr ServiceFlags SeedsServiceFlags() { return ServiceFlags(NODE_NETWORK | NODE_WITNESS); }
 
+/**
+ * Service flags we assume for addresses obtained from the DNS seeds and the
+ * fixed seeds, which don't come with service flags attached.
+ * BIP324 support can be safely assumed because the vast majority of listening nodes signals NODE_P2P_V2, and if the
+ * assumption is wrong for a given peer we simply reconnect using v1 transport.
+ */
+constexpr ServiceFlags SeedsAssumedServiceFlags() { return ServiceFlags(SeedsServiceFlags() | NODE_P2P_V2); }
+
 /**
  * Checks if a peer with the given service flags may be capable of having a
  * robust address-storage DB.