diff --git a/tracker/src/main/groovy/com/muwire/tracker/Pinger.groovy b/tracker/src/main/groovy/com/muwire/tracker/Pinger.groovy
index 44073fe1..7e2e1393 100644
--- a/tracker/src/main/groovy/com/muwire/tracker/Pinger.groovy
+++ b/tracker/src/main/groovy/com/muwire/tracker/Pinger.groovy
@@ -1,14 +1,113 @@
 package com.muwire.tracker
 
+import java.util.concurrent.ConcurrentHashMap
+import java.util.logging.Level
+
+import javax.annotation.PostConstruct
+
+import org.springframework.beans.factory.annotation.Autowired
 import org.springframework.stereotype.Component
 
+import com.muwire.core.Constants
 import com.muwire.core.Core
 
+import groovy.json.JsonOutput
+import groovy.util.logging.Log
+import net.i2p.client.I2PSession
+import net.i2p.client.I2PSessionMuxedListener
+import net.i2p.client.SendMessageOptions
+import net.i2p.client.datagram.I2PDatagramMaker
+import net.i2p.data.Base64
+
 @Component
+@Log
 class Pinger {
-    private final Core core
+    @Autowired
+    private Core core
     
-    Pinger(Core core) {
-        this.core = core
+    @Autowired
+    private SwarmManager swarmManager
+    
+    @Autowired
+    private TrackerProperties trackerProperties
+    
+    private final Map<UUID, PingInProgress> inFlight = new ConcurrentHashMap<>()
+    private final Timer expiryTimer = new Timer("pinger-timer",true)
+    
+    @PostConstruct
+    private void registerListener() {
+        core.getI2pSession().addMuxedSessionListener(new Listener(), I2PSession.PROTO_DATAGRAM, Constants.TRACKER_PORT)
+        expiryTimer.schedule({expirePings()} as TimerTask, 1000, 1000)
     }
+    
+    private void expirePings() {
+        final long now = System.currentTimeMillis()
+        for(Iterator<UUID> iter = inFlight.keySet().iterator(); iter.hasNext();) {
+            UUID uuid = iter.next()
+            PingInProgress ping = inFlight.get(uuid) 
+            if (now - ping.pingTime > trackerProperties.getSwarmParameters().getPingTimeout() * 1000L) {
+                iter.remove()
+                swarmManager.fail(ping.target)
+            }
+        }
+    }
+    
+    void ping(SwarmManager.HostAndIH target, long now) {
+        UUID uuid = UUID.randomUUID()
+        def ping = new PingInProgress(target, now)
+        inFlight.put(uuid, ping)
+        
+        def message = [:]
+        message.type = "TrackerPing"
+        message.version = 1
+        message.infoHash = Base64.encode(target.getInfoHash().getRoot())
+        message.uuid = uuid.toString()
+        
+        message = JsonOutput.toJson(message)
+        def maker = new I2PDatagramMaker(core.getI2pSession())
+        message = maker.makeI2PDatagram(message.bytes)
+        def options = new SendMessageOptions()
+        options.setSendLeaseSet(true)
+        core.getI2pSession().sendMessage(target.getHost().getPersona().getDestination(), message, 0, message.length, I2PSession.PROTO_DATAGRAM,
+            Constants.TRACKER_PORT, Constants.TRACKER_PORT, options)
+    }
+    
+    private static class PingInProgress {
+        private final SwarmManager.HostAndIH target
+        private final long pingTime
+        PingInProgress(SwarmManager.HostAndIH target, long pingTime) {
+            this.target = target
+            this.pingTime = pingTime
+        }
+    }
+    
+    private class Listener implements I2PSessionMuxedListener {
+
+        @Override
+        public void messageAvailable(I2PSession session, int msgId, long size) {
+        }
+
+        @Override
+        public void messageAvailable(I2PSession session, int msgId, long size, int proto, int fromport, int toport) {
+            // TODO Auto-generated method stub
+            
+        }
+
+        @Override
+        public void reportAbuse(I2PSession session, int severity) {
+            log.warning("reportabuse $session $severity")
+        }
+
+        @Override
+        public void disconnected(I2PSession session) {
+            log.severe("disconnected")
+        }
+
+        @Override
+        public void errorOccurred(I2PSession session, String message, Throwable error) {
+            log.log(Level.SEVERE,message,error)
+        }
+        
+    }
+    
 }
diff --git a/tracker/src/main/groovy/com/muwire/tracker/SwarmManager.groovy b/tracker/src/main/groovy/com/muwire/tracker/SwarmManager.groovy
index 56ae4a1a..4cb00348 100644
--- a/tracker/src/main/groovy/com/muwire/tracker/SwarmManager.groovy
+++ b/tracker/src/main/groovy/com/muwire/tracker/SwarmManager.groovy
@@ -90,6 +90,8 @@ class SwarmManager {
         }
         
         log.info("will ping $toPing")
+        
+        toPing.each { pinger.ping(it, now) }
     }
     
     private void query(Swarm swarm) {
@@ -132,9 +134,13 @@ class SwarmManager {
         swarms.get(infoHash)?.info()
     }
     
-    private static class HostAndIH {
-        private final Host host
-        private final InfoHash infoHash
+    void fail(HostAndIH target) {
+        swarms.get(target.infoHash)?.fail(target.host)
+    }
+    
+    public static class HostAndIH {
+        final Host host
+        final InfoHash infoHash
         HostAndIH(Host host, InfoHash infoHash) {
             this.host = host
             this.infoHash = infoHash
diff --git a/tracker/src/main/groovy/com/muwire/tracker/TrackerProperties.groovy b/tracker/src/main/groovy/com/muwire/tracker/TrackerProperties.groovy
index 994754df..3fcda9ef 100644
--- a/tracker/src/main/groovy/com/muwire/tracker/TrackerProperties.groovy
+++ b/tracker/src/main/groovy/com/muwire/tracker/TrackerProperties.groovy
@@ -25,5 +25,7 @@ class TrackerProperties {
         int pingInterval = 15
         /** how long to wait before declaring a host is dead, in minutes */
         int expiry = 60
+        /** how long to wait for a host to respond to a ping, in seconds */
+        int pingTimeout = 20
     }
 }