diff --git a/host-cache/src/main/groovy/com/muwire/hostcache/Crawler.groovy b/host-cache/src/main/groovy/com/muwire/hostcache/Crawler.groovy
index c4c9c004..aa280bbb 100644
--- a/host-cache/src/main/groovy/com/muwire/hostcache/Crawler.groovy
+++ b/host-cache/src/main/groovy/com/muwire/hostcache/Crawler.groovy
@@ -6,14 +6,16 @@ class Crawler {
 
     final def pinger
     final def hostPool
+	final int parallel
     
     final Map<Destination, Host> inFlight = new HashMap<>()
     
     UUID currentUUID
     
-    Crawler(pinger, hostPool) {
+    Crawler(pinger, hostPool, int parallel) {
         this.pinger = pinger
         this.hostPool = hostPool
+		this.parallel = parallel
     }
     
     synchronized def handleCrawlerPong(pong, Destination source) {
@@ -61,4 +63,16 @@ class Crawler {
     private static boolean parseBoolean(value) {
         return Boolean.parseBoolean(value.toString())
     }
+	
+	synchronized def startCrawl() {
+		if (!inFlight.isEmpty()) {
+			inFlight.values().each { hostPool.fail(it) }
+			inFlight.clear()
+		}
+		currentUUID = UUID.randomUUID()
+		hostPool.getUnverified(parallel).each { 
+			inFlight.put(it.destination, it)
+			pinger.ping(it, currentUUID)
+		}
+	}
 }
diff --git a/host-cache/src/test/groovy/com/muwire/hostcache/CrawlerTest.groovy b/host-cache/src/test/groovy/com/muwire/hostcache/CrawlerTest.groovy
index 7298db32..6b407346 100644
--- a/host-cache/src/test/groovy/com/muwire/hostcache/CrawlerTest.groovy
+++ b/host-cache/src/test/groovy/com/muwire/hostcache/CrawlerTest.groovy
@@ -1,5 +1,6 @@
 package com.muwire.hostcache
 
+import org.junit.After
 import org.junit.Before
 import org.junit.Test
 
@@ -17,21 +18,58 @@ class CrawlerTest {
 	
 	def crawler
 	
+	final Host host = new Host(destination: new Destination())
+	
+	final int parallel = 5
+	
 	@Before
 	void before() {
 		pingerMock = new MockFor(Pinger)
-		pinger = pingerMock.proxyInstance()
-		
 		hostPoolMock = new MockFor(HostPool)
+	}
+	
+	@After
+	void after() {
+		hostPoolMock.verify hostPool
+		pingerMock.verify pinger
+	}
+	
+	private def initCrawler() {
+		pinger = pingerMock.proxyInstance()
 		hostPool = hostPoolMock.proxyInstance()
+		crawler = new Crawler(pinger, hostPool, parallel)
 		
-		crawler = new Crawler(pinger, hostPool)
 	}
 	
 	@Test
 	void testBadJson() {
+		initCrawler()
 		def unpingedHost = new Host(destination : new Destination())
 		crawler.handleCrawlerPong(null, new Destination())
-		hostPoolMock.verify hostPool
+	}
+	
+	@Test
+	void testStartCrawl() {
+		hostPoolMock.demand.getUnverified { n ->
+			assert n == parallel
+			[host]
+		}
+		pingerMock.demand.ping { h,uuid -> assert h == host }
+		
+		initCrawler()
+		crawler.startCrawl()
+		
+	}
+	
+	@Test
+	void testFailsUnanswered() {
+		hostPoolMock.demand.getUnverified {n -> [host]}
+		hostPoolMock.demand.fail { h -> assert h == host }
+		hostPoolMock.demand.getUnverified {n -> [:]}
+		pingerMock.demand.ping {h,uuid -> }
+		initCrawler()
+		
+		crawler.startCrawl()
+		crawler.startCrawl()
 	}
 }