diff --git a/root/root.cpp b/root/root.cpp
index 6c7bde97..7c77bccd 100644
--- a/root/root.cpp
+++ b/root/root.cpp
@@ -126,14 +126,17 @@ using json = nlohmann::json;
  */
 struct RootPeer
 {
-	ZT_ALWAYS_INLINE RootPeer() : lastSend(0),lastReceive(0),lastEcho(0),lastHello(0),vProto(-1),vMajor(-1),vMinor(-1),vRev(-1) {}
+	ZT_ALWAYS_INLINE RootPeer() : v4s(-1),v6s(-1),lastSend(0),lastReceive(0),lastReceiveV4(0),lastReceiveV6(0),lastEcho(0),lastHello(0),vProto(-1),vMajor(-1),vMinor(-1),vRev(-1) {}
 	ZT_ALWAYS_INLINE ~RootPeer() { Utils::burn(key,sizeof(key)); }
 
 	Identity id;            // Identity
 	uint8_t key[32];        // Shared secret key
 	InetAddress ip4,ip6;    // IPv4 and IPv6 addresses
+	int v4s, v6s;           // IPv4 and IPv6 sockets
 	int64_t lastSend;       // Time of last send (any packet)
 	int64_t lastReceive;    // Time of last receive (any packet)
+	int64_t lastReceiveV4;  // Time of last IPv4 receive
+	int64_t lastReceiveV6;  // Time of last IPv6 receive
 	int64_t lastEcho;       // Time of last received ECHO
 	int64_t lastHello;      // Time of last received HELLO
 	int vProto;             // Protocol version or -1 if unknown
@@ -229,7 +232,7 @@ static ZT_ALWAYS_INLINE std::array< uint64_t,2 > ip6ToH128(const InetAddress &ip
 	return i128;
 }
 
-static void handlePacket(const int v4s,const int v6s,const InetAddress *const ip,Packet &pkt)
+static void handlePacket(const int sock,const InetAddress *const ip,Packet &pkt)
 {
 	char ipstr[128],ipstr2[128],astr[32],astr2[32],tmpstr[256];
 	const bool fragment = pkt[ZT_PACKET_FRAGMENT_IDX_FRAGMENT_INDICATOR] == ZT_PACKET_FRAGMENT_INDICATOR;
@@ -329,18 +332,27 @@ static void handlePacket(const int v4s,const int v6s,const InetAddress *const ip
 		// If we found the peer, update IP and/or time and handle certain key packet types that the
 		// root must concern itself with.
 		if (peer) {
-			if (ip->isV4())
-				peer->ip4 = ip;
-			else if (ip->isV6())
-				peer->ip6 = ip;
-
 			const int64_t now = OSUtils::now();
+
+			if (ip->isV4()) {
+				peer->ip4 = ip;
+				peer->v4s = sock;
+				peer->lastReceiveV4 = now;
+				if ((now - peer->lastReceiveV6) > ZT_PEER_ACTIVITY_TIMEOUT)
+					peer->v6s = -1;
+			} else if (ip->isV6()) {
+				peer->ip6 = ip;
+				peer->v6s = sock;
+				peer->lastReceiveV6 = now;
+				if ((now - peer->lastReceiveV4) > ZT_PEER_ACTIVITY_TIMEOUT)
+					peer->v4s = -1;
+			}
 			peer->lastReceive = now;
 
 			switch(pkt.verb()) {
 				case Packet::VERB_HELLO:
 					try {
-						if ((now - peer->lastHello) > 500) {
+						if ((now - peer->lastHello) > 250) {
 							peer->lastHello = now;
 
 							peer->vProto = (int)pkt[ZT_PROTO_VERB_HELLO_IDX_PROTOCOL_VERSION];
@@ -367,7 +379,7 @@ static void handlePacket(const int v4s,const int v6s,const InetAddress *const ip
 								}
 							}
 							pkt.armor(peer->key,true);
-							sendto(ip->isV4() ? v4s : v6s,pkt.data(),pkt.size(),SENDTO_FLAGS,(const struct sockaddr *)ip,(socklen_t)((ip->ss_family == AF_INET) ? sizeof(struct sockaddr_in) : sizeof(struct sockaddr_in6)));
+							sendto(sock,pkt.data(),pkt.size(),SENDTO_FLAGS,(const struct sockaddr *)ip,(socklen_t)((ip->ss_family == AF_INET) ? sizeof(struct sockaddr_in) : sizeof(struct sockaddr_in6)));
 
 							s_outputRate.log(now,pkt.size());
 							peer->lastSend = now;
@@ -388,7 +400,7 @@ static void handlePacket(const int v4s,const int v6s,const InetAddress *const ip
 							outp.append(((const uint8_t *)pkt.data()) + ZT_PACKET_IDX_PAYLOAD,pkt.size() - ZT_PACKET_IDX_PAYLOAD);
 							outp.compress();
 							outp.armor(peer->key,true);
-							sendto(ip->isV4() ? v4s : v6s,outp.data(),outp.size(),SENDTO_FLAGS,(const struct sockaddr *)ip,(socklen_t)((ip->ss_family == AF_INET) ? sizeof(struct sockaddr_in) : sizeof(struct sockaddr_in6)));
+							sendto(sock,outp.data(),outp.size(),SENDTO_FLAGS,(const struct sockaddr *)ip,(socklen_t)((ip->ss_family == AF_INET) ? sizeof(struct sockaddr_in) : sizeof(struct sockaddr_in6)));
 
 							s_outputRate.log(now,outp.size());
 							peer->lastSend = now;
@@ -400,6 +412,7 @@ static void handlePacket(const int v4s,const int v6s,const InetAddress *const ip
 				case Packet::VERB_WHOIS:
 					try {
 						std::vector< SharedPtr<RootPeer> > results;
+						results.reserve(4);
 						{
 							std::lock_guard<std::mutex> l(s_peersByVirtAddr_l);
 							for(unsigned int ptr=ZT_PACKET_IDX_PAYLOAD;(ptr+ZT_ADDRESS_LENGTH)<=pkt.size();ptr+=ZT_ADDRESS_LENGTH) {
@@ -419,7 +432,7 @@ static void handlePacket(const int v4s,const int v6s,const InetAddress *const ip
 							for(auto p=results.begin();p!=results.end();++p)
 								(*p)->id.serialize(pkt,false);
 							pkt.armor(peer->key,true);
-							sendto(ip->isV4() ? v4s : v6s,pkt.data(),pkt.size(),SENDTO_FLAGS,(const struct sockaddr *)ip,(socklen_t)((ip->ss_family == AF_INET) ? sizeof(struct sockaddr_in) : sizeof(struct sockaddr_in6)));
+							sendto(sock,pkt.data(),pkt.size(),SENDTO_FLAGS,(const struct sockaddr *)ip,(socklen_t)((ip->ss_family == AF_INET) ? sizeof(struct sockaddr_in) : sizeof(struct sockaddr_in6)));
 
 							s_outputRate.log(now,pkt.size());
 							peer->lastSend = now;
@@ -479,7 +492,7 @@ static void handlePacket(const int v4s,const int v6s,const InetAddress *const ip
 									if (l > 0) {
 										pkt.setAt<uint16_t>(countAt,(uint16_t)l);
 										pkt.armor(peer->key,true);
-										sendto(ip->isV4() ? v4s : v6s,pkt.data(),pkt.size(),SENDTO_FLAGS,(const struct sockaddr *)ip,(socklen_t)(ip->isV4() ? sizeof(struct sockaddr_in) : sizeof(struct sockaddr_in6)));
+										sendto(sock,pkt.data(),pkt.size(),SENDTO_FLAGS,(const struct sockaddr *)ip,(socklen_t)(ip->isV4() ? sizeof(struct sockaddr_in) : sizeof(struct sockaddr_in6)));
 
 										s_outputRate.log(now,pkt.size());
 										peer->lastSend = now;
@@ -531,14 +544,21 @@ static void handlePacket(const int v4s,const int v6s,const InetAddress *const ip
 	}
 
 	std::vector< std::pair< InetAddress *,SharedPtr<RootPeer> > > toAddrs;
+	toAddrs.reserve(4);
 	{
 		std::lock_guard<std::mutex> pbv_l(s_peersByVirtAddr_l);
 		auto peers = s_peersByVirtAddr.find(dest);
 		if (peers != s_peersByVirtAddr.end()) {
 			for(auto p=peers->second.begin();p!=peers->second.end();++p) {
-				if ((*p)->ip4) {
+				if (((*p)->v4s >= 0)&&((*p)->v6s >= 0)) {
+					if ((*p)->lastReceiveV4 > (*p)->lastReceiveV6) {
+						toAddrs.emplace_back(std::pair< InetAddress *,SharedPtr<RootPeer> >(&((*p)->ip4),*p));
+					} else {
+						toAddrs.emplace_back(std::pair< InetAddress *,SharedPtr<RootPeer> >(&((*p)->ip6),*p));
+					}
+				} else if ((*p)->v4s >= 0) {
 					toAddrs.emplace_back(std::pair< InetAddress *,SharedPtr<RootPeer> >(&((*p)->ip4),*p));
-				} else if ((*p)->ip6) {
+				} else if ((*p)->v6s >= 0) {
 					toAddrs.emplace_back(std::pair< InetAddress *,SharedPtr<RootPeer> >(&((*p)->ip6),*p));
 				}
 			}
@@ -555,7 +575,7 @@ static void handlePacket(const int v4s,const int v6s,const InetAddress *const ip
 		if (sources != s_peersByVirtAddr.end()) {
 			for(auto a=sources->second.begin();a!=sources->second.end();++a) {
 				for(auto b=toAddrs.begin();b!=toAddrs.end();++b) {
-					if (((*a)->ip6)&&(b->second->ip6)) {
+					if (((*a)->v6s >= 0)&&(b->second->v6s >= 0)) {
 						//printf("* introducing %s(%s) to %s(%s)" ZT_EOL_S,ip->toString(ipstr),source.toString(astr),b->second->ip6.toString(ipstr2),dest.toString(astr2));
 
 						// Introduce source to destination (V6)
@@ -566,7 +586,7 @@ static void handlePacket(const int v4s,const int v6s,const InetAddress *const ip
 						outp.append((uint8_t)16);
 						outp.append((const uint8_t *)(b->second->ip6.rawIpData()),16);
 						outp.armor((*a)->key,true);
-						sendto(v6s,outp.data(),outp.size(),SENDTO_FLAGS,(const struct sockaddr *)&((*a)->ip6),(socklen_t)sizeof(struct sockaddr_in6));
+						sendto((*a)->v6s,outp.data(),outp.size(),SENDTO_FLAGS,(const struct sockaddr *)&((*a)->ip6),(socklen_t)sizeof(struct sockaddr_in6));
 
 						s_outputRate.log(now,outp.size());
 						(*a)->lastSend = now;
@@ -579,12 +599,12 @@ static void handlePacket(const int v4s,const int v6s,const InetAddress *const ip
 						outp.append((uint8_t)16);
 						outp.append((const uint8_t *)((*a)->ip6.rawIpData()),16);
 						outp.armor(b->second->key,true);
-						sendto(v6s,outp.data(),outp.size(),SENDTO_FLAGS,(const struct sockaddr *)&(b->second->ip6),(socklen_t)sizeof(struct sockaddr_in6));
+						sendto(b->second->v6s,outp.data(),outp.size(),SENDTO_FLAGS,(const struct sockaddr *)&(b->second->ip6),(socklen_t)sizeof(struct sockaddr_in6));
 
 						s_outputRate.log(now,outp.size());
 						b->second->lastSend = now;
 					}
-					if (((*a)->ip4)&&(b->second->ip4)) {
+					if (((*a)->v4s >= 0)&&(b->second->v4s >= 0)) {
 						//printf("* introducing %s(%s) to %s(%s)" ZT_EOL_S,ip->toString(ipstr),source.toString(astr),b->second->ip4.toString(ipstr2),dest.toString(astr2));
 
 						// Introduce source to destination (V4)
@@ -595,7 +615,7 @@ static void handlePacket(const int v4s,const int v6s,const InetAddress *const ip
 						outp.append((uint8_t)4);
 						outp.append((const uint8_t *)b->second->ip4.rawIpData(),4);
 						outp.armor((*a)->key,true);
-						sendto(v4s,outp.data(),outp.size(),SENDTO_FLAGS,(const struct sockaddr *)&((*a)->ip4),(socklen_t)sizeof(struct sockaddr_in));
+						sendto((*a)->v4s,outp.data(),outp.size(),SENDTO_FLAGS,(const struct sockaddr *)&((*a)->ip4),(socklen_t)sizeof(struct sockaddr_in));
 
 						s_outputRate.log(now,outp.size());
 						(*a)->lastSend = now;
@@ -608,7 +628,7 @@ static void handlePacket(const int v4s,const int v6s,const InetAddress *const ip
 						outp.append((uint8_t)4);
 						outp.append((const uint8_t *)((*a)->ip4.rawIpData()),4);
 						outp.armor(b->second->key,true);
-						sendto(v4s,outp.data(),outp.size(),SENDTO_FLAGS,(const struct sockaddr *)&(b->second->ip4),(socklen_t)sizeof(struct sockaddr_in));
+						sendto(b->second->v6s,outp.data(),outp.size(),SENDTO_FLAGS,(const struct sockaddr *)&(b->second->ip4),(socklen_t)sizeof(struct sockaddr_in));
 
 						s_outputRate.log(now,outp.size());
 						b->second->lastSend = now;
@@ -619,7 +639,7 @@ static void handlePacket(const int v4s,const int v6s,const InetAddress *const ip
 	}
 
 	for(auto i=toAddrs.begin();i!=toAddrs.end();++i) {
-		if (sendto(i->first->isV4() ? v4s : v6s,pkt.data(),pkt.size(),SENDTO_FLAGS,(const struct sockaddr *)i->first,(socklen_t)(i->first->isV4() ? sizeof(struct sockaddr_in) : sizeof(struct sockaddr_in6))) > 0) {
+		if (sendto(i->first->isV4() ? i->second->v4s : i->second->v6s,pkt.data(),pkt.size(),SENDTO_FLAGS,(const struct sockaddr *)i->first,(socklen_t)(i->first->isV4() ? sizeof(struct sockaddr_in) : sizeof(struct sockaddr_in6))) > 0) {
 			s_outputRate.log(now,pkt.size());
 			s_forwardRate.log(now,pkt.size());
 			i->second->lastSend = now;
@@ -639,16 +659,16 @@ static int bindSocket(struct sockaddr *const bindAddr)
 	}
 
 	int f = 16777216;
-	while (f > 131072) {
+	while (f > 65536) {
 		if (setsockopt(s,SOL_SOCKET,SO_RCVBUF,(const char *)&f,sizeof(f)) == 0)
 			break;
-		f -= 131072;
+		f -= 65536;
 	}
 	f = 16777216;
-	while (f > 131072) {
+	while (f > 65536) {
 		if (setsockopt(s,SOL_SOCKET,SO_SNDBUF,(const char *)&f,sizeof(f)) == 0)
 			break;
-		f -= 131072;
+		f -= 65536;
 	}
 
 	if (bindAddr->sa_family == AF_INET6) {
@@ -913,7 +933,7 @@ int main(int argc,char **argv)
 						if ((pl >= ZT_PROTO_MIN_FRAGMENT_LENGTH)&&(pl <= ZT_PROTO_MAX_PACKET_LENGTH)) {
 							try {
 								pkt->setSize((unsigned int)pl);
-								handlePacket(s4,s6,reinterpret_cast<const InetAddress *>(&in6),*pkt);
+								handlePacket(s6,reinterpret_cast<const InetAddress *>(&in6),*pkt);
 							} catch (std::exception &exc) {
 								char ipstr[128];
 								printf("WARNING: unexpected exception handling packet from %s: %s" ZT_EOL_S,reinterpret_cast<const InetAddress *>(&in6)->toString(ipstr),exc.what());
@@ -943,7 +963,7 @@ int main(int argc,char **argv)
 						if ((pl >= ZT_PROTO_MIN_FRAGMENT_LENGTH)&&(pl <= ZT_PROTO_MAX_PACKET_LENGTH)) {
 							try {
 								pkt->setSize((unsigned int)pl);
-								handlePacket(s4,s6,reinterpret_cast<const InetAddress *>(&in4),*pkt);
+								handlePacket(s4,reinterpret_cast<const InetAddress *>(&in4),*pkt);
 							} catch (std::exception &exc) {
 								char ipstr[128];
 								printf("WARNING: unexpected exception handling packet from %s: %s" ZT_EOL_S,reinterpret_cast<const InetAddress *>(&in4)->toString(ipstr),exc.what());
@@ -1021,7 +1041,7 @@ int main(int argc,char **argv)
 					"{\"address\":\"" << (*p)->id.address().toString(tmp) << "\""
 					",\"latency\":-1"
 					",\"paths\":[";
-					if ((*p)->ip4) {
+					if ((*p)->v4s >= 0) {
 						o <<
 						"{\"active\":true"
 						",\"address\":\"" << (*p)->ip4.toIpString(tmp) << "\\/" << (*p)->ip4.port() << "\""
@@ -1031,8 +1051,8 @@ int main(int argc,char **argv)
 						",\"preferred\":true"
 						",\"trustedPathId\":0}";
 					}
-					if ((*p)->ip6) {
-						if ((*p)->ip4)
+					if ((*p)->v6s >= 0) {
+						if ((*p)->v4s >= 0)
 							o << ',';
 						o <<
 						"{\"active\":true"
@@ -1074,9 +1094,9 @@ int main(int argc,char **argv)
 				{
 					std::lock_guard<std::mutex> l(s_peers_l);
 					for(auto p=s_peers.begin();p!=s_peers.end();++p) {
-						if ((*p)->ip4)
+						if ((*p)->v4s >= 0)
 							ips[(*p)->ip4].insert((*p)->id.address());
-						if ((*p)->ip6)
+						if ((*p)->v6s >= 0)
 							ips[(*p)->ip6].insert((*p)->id.address());
 					}
 				}
@@ -1257,13 +1277,13 @@ int main(int argc,char **argv)
 				{
 					char ip4[128],ip6[128],ver[128];
 					for(auto p=sp.begin();p!=sp.end();++p) {
-						if ((*p)->ip4) {
+						if ((*p)->v4s >= 0) {
 							(*p)->ip4.toString(ip4);
 						} else {
 							ip4[0] = '-';
 							ip4[1] = 0;
 						}
-						if ((*p)->ip6) {
+						if ((*p)->v6s >= 0) {
 							(*p)->ip6.toString(ip6);
 						} else {
 							ip6[0] = '-';