1 files changed, 30 insertions, 1 deletions

diff --git a/node/IncomingPacket.cpp b/node/IncomingPacket.cpp
index b0d65159..32229ba6 100644
--- a/node/IncomingPacket.cpp
+++ b/node/IncomingPacket.cpp
@@ -294,7 +294,36 @@ bool IncomingPacket::_doHELLO(const RuntimeEnvironment *RR)
 		outp.append((unsigned char)ZEROTIER_ONE_VERSION_MAJOR);
 		outp.append((unsigned char)ZEROTIER_ONE_VERSION_MINOR);
 		outp.append((uint16_t)ZEROTIER_ONE_VERSION_REVISION);
-		_remoteAddress.serialize(outp);
+		if (protoVersion >= 5) {
+			_remoteAddress.serialize(outp);
+		} else {
+			/* LEGACY COMPATIBILITY HACK:
+			 *
+			 * For a while now (since 1.0.3), ZeroTier has recognized changes in
+			 * its network environment empirically by examining its external network
+			 * address as reported by trusted peers. In versions prior to 1.1.0
+			 * (protocol version < 5), they did this by saving a snapshot of this
+			 * information (in SelfAwareness.hpp) keyed by reporting device ID and
+			 * address type.
+			 *
+			 * This causes problems when clustering is combined with symmetric NAT.
+			 * Symmetric NAT remaps ports, so different endpoints in a cluster will
+			 * report back different exterior addresses. Since the old code keys
+			 * this by device ID and not sending physical address and compares the
+			 * entire address including port, it constantly thinks its external
+			 * surface is changing and resets connections when talking to a cluster.
+			 *
+			 * In new code we key by sending physical address and device and we also
+			 * take the more conservative position of only interpreting changes in
+			 * IP address (neglecting port) as a change in network topology that
+			 * necessitates a reset. But we can make older clients work here by
+			 * nulling out the port field. Since this info is only used for empirical
+			 * detection of link changes, it doesn't break anything else.
+			 */
+			InetAddress tmpa(_remoteAddress);
+			tmpa.setPort(0);
+			tmpa.serialize(outp);
+		}
 
 		if ((worldId != ZT_WORLD_ID_NULL)&&(RR->topology->worldTimestamp() > worldTimestamp)&&(worldId == RR->topology->worldId())) {
 			World w(RR->topology->world());