Make network multicast breadth/depth parameters configurable on a per-net basis.

netconf-service/netconf.cpp

@@ -204,15 +204,19 @@ int main(int argc,char **argv)
 				}
 
 				bool isOpen = false;
+				unsigned int mcb = 3;
+				unsigned int mcd = 6;
 				std::string name,desc;
 				{
 					Query q = dbCon->query();
-					q << "SELECT name,`desc`,isOpen FROM Network WHERE id = " << nwid;
+					q << "SELECT name,`desc`,isOpen,multicastPropagationBreadth,multicastPropagationDepth FROM Network WHERE id = " << nwid;
 					StoreQueryResult rs = q.store();
 					if (rs.num_rows() > 0) {
 						name = rs[0]["name"].c_str();
 						desc = rs[0]["desc"].c_str();
 						isOpen = ((int)rs[0]["isOpen"] > 0);
+						mcb = (unsigned int)rs[0]["multicastPropagationBreadth"];
+						mcd = (unsigned int)rs[0]["multicastPropagationDepth"];
 					} else {
 						Dictionary response;
 						response["peer"] = peerIdentity.address().toString();
@@ -293,6 +297,10 @@ int main(int argc,char **argv)
 				sprintf(buf,"%llx",(unsigned long long)Utils::now());
 				netconf["ts"] = buf;
 				netconf["peer"] = peerIdentity.address().toString();
+				sprintf(buf,"%x",mcb);
+				netconf["mcb"] = mcb;
+				sprintf(buf,"%x",mcd);
+				netconf["mcd"] = mcd;
 
 				if (!isOpen) {
 					// TODO: handle closed networks, look up private membership,

node/Constants.hpp

@@ -233,25 +233,12 @@ error_no_ZT_ARCH_defined;
 /**
  * Breadth of tree for rumor mill multicast propagation
  */
-#define ZT_MULTICAST_PROPAGATION_BREADTH 4
+#define ZT_MULTICAST_DEFAULT_PROPAGATION_BREADTH 3
 
 /**
  * Depth of tree for rumor mill multicast propagation
- *
- * The maximum number of peers who can receive a multicast is equal to
- * the sum of BREADTH^i where I is from 1 to DEPTH. This ignores the effect
- * of the rate limiting algorithm or bloom filter collisions.
- *
- * 5 results in a max of 1364 recipients for a given multicast. With a limit
- * of 50 bytes/sec (average) for multicast, this results in a worst case of
- * around 68kb/sec of multicast traffic. FYI the average multicast traffic
- * from a Mac seems to be about ~25bytes/sec. Windows measurements are TBD.
- * Linux is quieter than Mac.
- *
- * This are eventually going to become per-network tunable parameters, along
- * with per-network peer multicast rate limits.
  */
-#define ZT_MULTICAST_PROPAGATION_DEPTH 5
+#define ZT_MULTICAST_DEFAULT_PROPAGATION_DEPTH 6
 
 /**
  * Length of ring buffer history of recent multicast packets

node/Multicaster.hpp

@@ -52,9 +52,6 @@
 #include "CMWC4096.hpp"
 #include "C25519.hpp"
 
-// Maximum sample size to pick during choice of multicast propagation peers
-#define ZT_MULTICAST_PICK_MAX_SAMPLE_SIZE (ZT_MULTICAST_PROPAGATION_BREADTH * 8)
-
 namespace ZeroTier {
 
 /**
@@ -253,7 +250,7 @@ public:
 		Mutex::Lock _l(_multicastMemberships_m);
 		std::map< MulticastChannel,std::vector<MulticastMembership> >::iterator mm(_multicastMemberships.find(MulticastChannel(nwid,mg)));
 		if ((mm != _multicastMemberships.end())&&(!mm->second.empty())) {
-			for(unsigned int stries=0;((stries<ZT_MULTICAST_PICK_MAX_SAMPLE_SIZE)&&(chosen < max));++stries) {
+			for(unsigned int stries=0,stmax=(max*10);((stries<stmax)&&(chosen < max));++stries) {
 				MulticastMembership &m = mm->second[prng.next32() % mm->second.size()];
 				unsigned int sum = m.first.sum();
 				if (
@@ -320,7 +317,7 @@ public:
 			Mutex::Lock _l(_multicastMemberships_m);
 			std::map< MulticastChannel,std::vector<MulticastMembership> >::iterator mm(_multicastMemberships.find(MulticastChannel(nwid,mg)));
 			if ((mm != _multicastMemberships.end())&&(!mm->second.empty())) {
-				for(unsigned int stries=0;stries<ZT_MULTICAST_PICK_MAX_SAMPLE_SIZE;++stries) {
+				for(unsigned int stries=0,stmax=(max*10);stries<stmax;++stries) {
 					MulticastMembership &m = mm->second[prng.next32() % mm->second.size()];
 					if (
 					     ((now - m.second) < ZT_MULTICAST_LIKE_EXPIRE)&& /* LIKE is not expired */

node/Network.cpp

@@ -159,6 +159,8 @@ SharedPtr<Network> Network::newInstance(const RuntimeEnvironment *renv,uint64_t
 	nw->_ready = false; // disable handling of Ethernet frames during construct
 	nw->_r = renv;
 	nw->_tap = new EthernetTap(renv,tag,renv->identity.address().toMAC(),ZT_IF_MTU,&_CBhandleTapData,nw.ptr());
+	nw->_multicastPropagationBreadth = 0;
+	nw->_multicastPropagationDepth = 0;
 	memset(nw->_etWhitelist,0,sizeof(nw->_etWhitelist));
 	nw->_id = id;
 	nw->_lastConfigUpdate = 0;
@@ -179,6 +181,8 @@ void Network::setConfiguration(const Network::Config &conf)
 			_configuration = conf;
 			_myCertificate = conf.certificateOfMembership();
 			_mcRates = conf.multicastRates();
+			_multicastPropagationBreadth = conf.multicastPropagationBreadth();
+			_multicastPropagationDepth = conf.multicastPropagationDepth();
 			_lastConfigUpdate = Utils::now();
 
 			_tap->setIps(conf.staticAddresses());

node/Network.hpp

@@ -317,6 +317,28 @@ public:
 			return get("desc",std::string());
 		}
 
+		/**
+		 * @return Breadth for multicast propagation
+		 */
+		inline unsigned int multicastPropagationBreadth() const
+		{
+			const_iterator mcb(find("mcb"));
+			if (mcb == end())
+				return ZT_MULTICAST_DEFAULT_PROPAGATION_BREADTH;
+			return Utils::hexStrToUInt(mcb->second.c_str());
+		}
+
+		/**
+		 * @return Depth for multicast propagation
+		 */
+		inline unsigned int multicastPropagationDepth() const
+		{
+			const_iterator mcd(find("mcd"));
+			if (mcd == end())
+				return ZT_MULTICAST_DEFAULT_PROPAGATION_DEPTH;
+			return Utils::hexStrToUInt(mcd->second.c_str());
+		}
+
 		/**
 		 * @return Certificate of membership for this network, or empty cert if none
 		 */
@@ -586,6 +608,24 @@ public:
 		//return tmp;
 	}
 
+	/**
+	 * @return Breadth for multicast rumor mill propagation
+	 */
+	inline unsigned int multicastPropagationBreadth() const
+		throw()
+	{
+		return _multicastPropagationBreadth;
+	}
+
+	/**
+	 * @return Depth for multicast rumor mill propagation
+	 */
+	inline unsigned int multicastPropagationDepth() const
+		throw()
+	{
+		return _multicastPropagationDepth;
+	}
+
 private:
 	static void _CBhandleTapData(void *arg,const MAC &from,const MAC &to,unsigned int etherType,const Buffer<4096> &data);
 	void _restoreState();
@@ -606,6 +646,8 @@ private:
 	Config _configuration;
 	CertificateOfMembership _myCertificate; // memoized from _configuration
 	MulticastRates _mcRates; // memoized from _configuration
+	unsigned int _multicastPropagationBreadth; // memoized from _configuration
+	unsigned int _multicastPropagationDepth; // memoized from _configuration
 
 	// Ethertype whitelist bit field, set from config, for really fast lookup
 	unsigned char _etWhitelist[65536 / 8];

node/PacketDecoder.cpp

@@ -538,14 +538,14 @@ bool PacketDecoder::_doMULTICAST_FRAME(const RuntimeEnvironment *_r,const Shared
 				_r->multicaster->addToDedupHistory(mccrc,now);
 			}
 
-			if (++hops >= ZT_MULTICAST_PROPAGATION_DEPTH) {
+			if (++hops >= network->multicastPropagationDepth()) {
 				TRACE("not propagating MULTICAST_FRAME from original submitter %s, received from %s(%s): max depth reached",originalSubmitterAddress.toString().c_str(),source().toString().c_str(),_remoteAddress.toString().c_str());
 				return true;
 			}
 
 			Address upstream(source()); // save this since we might mangle it below
 			Multicaster::MulticastBloomFilter bloom(field(ZT_PROTO_VERB_MULTICAST_FRAME_IDX_BLOOM_FILTER,ZT_PROTO_VERB_MULTICAST_FRAME_BLOOM_FILTER_SIZE_BYTES));
-			SharedPtr<Peer> propPeers[ZT_MULTICAST_PROPAGATION_BREADTH];
+			SharedPtr<Peer> propPeers[16];
 			unsigned int np = 0;
 
 			if (_r->topology->amSupernode()) {
@@ -567,7 +567,7 @@ bool PacketDecoder::_doMULTICAST_FRAME(const RuntimeEnvironment *_r,const Shared
 					originalSubmitterAddress,
 					upstream,
 					bloom,
-					ZT_MULTICAST_PROPAGATION_BREADTH,
+					std::min(network->multicastPropagationBreadth(),(unsigned int)16), // 16 is a sanity check
 					propPeers,
 					now);
 			} else if (isDuplicate) {
@@ -584,7 +584,7 @@ bool PacketDecoder::_doMULTICAST_FRAME(const RuntimeEnvironment *_r,const Shared
 					originalSubmitterAddress,
 					upstream,
 					bloom,
-					ZT_MULTICAST_PROPAGATION_BREADTH,
+					std::min(network->multicastPropagationBreadth(),(unsigned int)16), // 16 is a sanity check
 					propPeers,
 					now);
 			}

node/Switch.cpp

@@ -119,7 +119,7 @@ void Switch::onLocalEthernet(const SharedPtr<Network> &network,const MAC &from,c
 		}
 
 		Multicaster::MulticastBloomFilter bloom;
-		SharedPtr<Peer> propPeers[ZT_MULTICAST_PROPAGATION_BREADTH];
+		SharedPtr<Peer> propPeers[16];
 		unsigned int np = _r->multicaster->pickSocialPropagationPeers(
 			*(_r->prng),
 			*(_r->topology),
@@ -128,7 +128,7 @@ void Switch::onLocalEthernet(const SharedPtr<Network> &network,const MAC &from,c
 			_r->identity.address(),
 			Address(),
 			bloom,
-			ZT_MULTICAST_PROPAGATION_BREADTH,
+			std::min(network->multicastPropagationBreadth(),(unsigned int)16), // 16 is a sanity check
 			propPeers,
 			now);