diff --git a/apps/config/src/main/java/org/onlab/onos/config/AddressEntry.java b/apps/config/src/main/java/org/onlab/onos/config/AddressEntry.java
index 318aebd..081efed 100644
--- a/apps/config/src/main/java/org/onlab/onos/config/AddressEntry.java
+++ b/apps/config/src/main/java/org/onlab/onos/config/AddressEntry.java
@@ -3,8 +3,6 @@
 import java.util.List;
 
 import org.codehaus.jackson.annotate.JsonProperty;
-import org.onlab.packet.IpPrefix;
-import org.onlab.packet.MacAddress;
 
 /**
  * Represents a set of addresses bound to a port.
@@ -12,8 +10,8 @@
 public class AddressEntry {
     private String dpid;
     private short portNumber;
-    private List<IpPrefix> ipAddresses;
-    private MacAddress macAddress;
+    private List<String> ipAddresses;
+    private String macAddress;
 
     public String getDpid() {
         return dpid;
@@ -33,21 +31,21 @@
         this.portNumber = portNumber;
     }
 
-    public List<IpPrefix> getIpAddresses() {
+    public List<String> getIpAddresses() {
         return ipAddresses;
     }
 
     @JsonProperty("ips")
-    public void setIpAddresses(List<IpPrefix> ipAddresses) {
-        this.ipAddresses = ipAddresses;
+    public void setIpAddresses(List<String> strIps) {
+        this.ipAddresses = strIps;
     }
 
-    public MacAddress getMacAddress() {
+    public String getMacAddress() {
         return macAddress;
     }
 
     @JsonProperty("mac")
-    public void setMacAddress(MacAddress macAddress) {
+    public void setMacAddress(String macAddress) {
         this.macAddress = macAddress;
     }
 }
diff --git a/apps/config/src/main/java/org/onlab/onos/config/NetworkConfigReader.java b/apps/config/src/main/java/org/onlab/onos/config/NetworkConfigReader.java
index 985c4a2..4f1a48a 100644
--- a/apps/config/src/main/java/org/onlab/onos/config/NetworkConfigReader.java
+++ b/apps/config/src/main/java/org/onlab/onos/config/NetworkConfigReader.java
@@ -5,6 +5,8 @@
 import java.io.File;
 import java.io.FileNotFoundException;
 import java.io.IOException;
+import java.util.HashSet;
+import java.util.Set;
 
 import org.apache.felix.scr.annotations.Activate;
 import org.apache.felix.scr.annotations.Component;
@@ -17,10 +19,10 @@
 import org.onlab.onos.net.PortNumber;
 import org.onlab.onos.net.host.HostAdminService;
 import org.onlab.onos.net.host.PortAddresses;
+import org.onlab.packet.IpPrefix;
+import org.onlab.packet.MacAddress;
 import org.slf4j.Logger;
 
-import com.google.common.collect.Sets;
-
 /**
  * Simple configuration module to read in supplementary network configuration
  * from a file.
@@ -51,9 +53,29 @@
                         DeviceId.deviceId(dpidToUri(entry.getDpid())),
                         PortNumber.portNumber(entry.getPortNumber()));
 
+                Set<IpPrefix> ipAddresses = new HashSet<IpPrefix>();
+
+                for (String strIp : entry.getIpAddresses()) {
+                    try {
+                        IpPrefix address = IpPrefix.valueOf(strIp);
+                        ipAddresses.add(address);
+                    } catch (IllegalArgumentException e) {
+                        log.warn("Bad format for IP address in config: {}", strIp);
+                    }
+                }
+
+                MacAddress macAddress = null;
+                if (entry.getMacAddress() != null) {
+                    try {
+                        macAddress = MacAddress.valueOf(entry.getMacAddress());
+                    } catch (IllegalArgumentException e) {
+                        log.warn("Bad format for MAC address in config: {}",
+                                entry.getMacAddress());
+                    }
+                }
+
                 PortAddresses addresses = new PortAddresses(cp,
-                        Sets.newHashSet(entry.getIpAddresses()),
-                        entry.getMacAddress());
+                        ipAddresses, macAddress);
 
                 hostAdminService.bindAddressesToPort(addresses);
             }
diff --git a/core/net/src/main/java/org/onlab/onos/net/host/impl/HostManager.java b/core/net/src/main/java/org/onlab/onos/net/host/impl/HostManager.java
index e3f53fe..88b6923 100644
--- a/core/net/src/main/java/org/onlab/onos/net/host/impl/HostManager.java
+++ b/core/net/src/main/java/org/onlab/onos/net/host/impl/HostManager.java
@@ -1,5 +1,10 @@
 package org.onlab.onos.net.host.impl;
 
+import static com.google.common.base.Preconditions.checkNotNull;
+import static org.slf4j.LoggerFactory.getLogger;
+
+import java.util.Set;
+
 import org.apache.felix.scr.annotations.Activate;
 import org.apache.felix.scr.annotations.Component;
 import org.apache.felix.scr.annotations.Deactivate;
@@ -12,6 +17,7 @@
 import org.onlab.onos.net.DeviceId;
 import org.onlab.onos.net.Host;
 import org.onlab.onos.net.HostId;
+import org.onlab.onos.net.device.DeviceService;
 import org.onlab.onos.net.host.HostAdminService;
 import org.onlab.onos.net.host.HostDescription;
 import org.onlab.onos.net.host.HostEvent;
@@ -23,6 +29,7 @@
 import org.onlab.onos.net.host.HostStore;
 import org.onlab.onos.net.host.HostStoreDelegate;
 import org.onlab.onos.net.host.PortAddresses;
+import org.onlab.onos.net.packet.PacketService;
 import org.onlab.onos.net.provider.AbstractProviderRegistry;
 import org.onlab.onos.net.provider.AbstractProviderService;
 import org.onlab.packet.IpAddress;
@@ -31,11 +38,6 @@
 import org.onlab.packet.VlanId;
 import org.slf4j.Logger;
 
-import java.util.Set;
-
-import static com.google.common.base.Preconditions.checkNotNull;
-import static org.slf4j.LoggerFactory.getLogger;
-
 /**
  * Provides basic implementation of the host SB &amp; NB APIs.
  */
@@ -59,12 +61,22 @@
     @Reference(cardinality = ReferenceCardinality.MANDATORY_UNARY)
     protected EventDeliveryService eventDispatcher;
 
+    @Reference(cardinality = ReferenceCardinality.MANDATORY_UNARY)
+    protected DeviceService deviceService;
+
+    @Reference(cardinality = ReferenceCardinality.MANDATORY_UNARY)
+    protected PacketService packetService;
+
+    private HostMonitor monitor;
 
     @Activate
     public void activate() {
+        log.info("Started");
         store.setDelegate(delegate);
         eventDispatcher.addSink(HostEvent.class, listenerRegistry);
-        log.info("Started");
+
+        monitor = new HostMonitor(deviceService,  packetService, this);
+
     }
 
     @Deactivate
@@ -76,6 +88,8 @@
 
     @Override
     protected HostProviderService createProviderService(HostProvider provider) {
+        monitor.registerHostProvider(provider);
+
         return new InternalHostProviderService(provider);
     }
 
@@ -126,12 +140,12 @@
 
     @Override
     public void startMonitoringIp(IpAddress ip) {
-        // TODO pass through to HostMonitor
+        monitor.addMonitoringFor(ip);
     }
 
     @Override
     public void stopMonitoringIp(IpAddress ip) {
-        // TODO pass through to HostMonitor
+        monitor.stopMonitoring(ip);
     }
 
     @Override
diff --git a/core/net/src/main/java/org/onlab/onos/net/host/impl/HostMonitor.java b/core/net/src/main/java/org/onlab/onos/net/host/impl/HostMonitor.java
index a5aa13e..9f8dd48 100644
--- a/core/net/src/main/java/org/onlab/onos/net/host/impl/HostMonitor.java
+++ b/core/net/src/main/java/org/onlab/onos/net/host/impl/HostMonitor.java
@@ -2,10 +2,11 @@
 
 import java.nio.ByteBuffer;
 import java.util.ArrayList;
-import java.util.Collections;
 import java.util.HashSet;
 import java.util.List;
+import java.util.Map;
 import java.util.Set;
+import java.util.concurrent.ConcurrentHashMap;
 import java.util.concurrent.TimeUnit;
 
 import org.jboss.netty.util.Timeout;
@@ -21,19 +22,19 @@
 import org.onlab.onos.net.flow.instructions.Instruction;
 import org.onlab.onos.net.flow.instructions.Instructions;
 import org.onlab.onos.net.host.HostProvider;
-import org.onlab.onos.net.host.HostService;
-import org.onlab.onos.net.host.HostStore;
 import org.onlab.onos.net.host.PortAddresses;
 import org.onlab.onos.net.packet.DefaultOutboundPacket;
 import org.onlab.onos.net.packet.OutboundPacket;
 import org.onlab.onos.net.packet.PacketService;
-import org.onlab.onos.net.topology.TopologyService;
+import org.onlab.onos.net.provider.ProviderId;
 import org.onlab.packet.ARP;
 import org.onlab.packet.Ethernet;
 import org.onlab.packet.IpAddress;
 import org.onlab.packet.IpPrefix;
 import org.onlab.packet.MacAddress;
 import org.onlab.util.Timer;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
 
 /**
  * Monitors hosts on the dataplane to detect changes in host data.
@@ -43,9 +44,7 @@
  * probe for hosts that have not yet been detected (specified by IP address).
  */
 public class HostMonitor implements TimerTask {
-
-    private static final byte[] DEFAULT_MAC_ADDRESS =
-            MacAddress.valueOf("00:00:00:00:00:01").getAddress();
+    private static final Logger log = LoggerFactory.getLogger(HostMonitor.class);
 
     private static final byte[] ZERO_MAC_ADDRESS =
             MacAddress.valueOf("00:00:00:00:00:00").getAddress();
@@ -54,59 +53,77 @@
     private static final byte[] BROADCAST_MAC =
             MacAddress.valueOf("ff:ff:ff:ff:ff:ff").getAddress();
 
-    private final HostService hostService;
-    private final TopologyService topologyService;
-    private final DeviceService deviceService;
-    private final HostProvider hostProvider;
-    private final PacketService packetService;
-    private final HostStore hostStore;
+    private DeviceService deviceService;
+    private PacketService packetService;
+    private HostManager hostManager;
 
     private final Set<IpAddress> monitoredAddresses;
 
+    private final Map<ProviderId, HostProvider> hostProviders;
+
     private final long probeRate;
 
     private final Timeout timeout;
 
-    public HostMonitor(HostService hostService, TopologyService topologyService,
+    public HostMonitor(
             DeviceService deviceService,
-            HostProvider hostProvider, PacketService packetService,
-            HostStore hostStore) {
-        this.hostService = hostService;
-        this.topologyService = topologyService;
+            PacketService packetService,
+            HostManager hostService) {
+
         this.deviceService = deviceService;
-        this.hostProvider = hostProvider;
         this.packetService = packetService;
-        this.hostStore = hostStore;
+        this.hostManager = hostService;
 
         monitoredAddresses = new HashSet<>();
+        hostProviders = new ConcurrentHashMap<>();
 
         probeRate = 30000; // milliseconds
 
         timeout = Timer.getTimer().newTimeout(this, 0, TimeUnit.MILLISECONDS);
+
+        addDefaultAddresses();
     }
 
-    public void addMonitoringFor(IpAddress ip) {
+    private void addDefaultAddresses() {
+        //monitoredAddresses.add(IpAddress.valueOf("10.0.0.1"));
+    }
+
+    void addMonitoringFor(IpAddress ip) {
         monitoredAddresses.add(ip);
     }
 
-    public void stopMonitoring(IpAddress ip) {
+    void stopMonitoring(IpAddress ip) {
         monitoredAddresses.remove(ip);
     }
 
-    public void shutdown() {
+    void shutdown() {
         timeout.cancel();
     }
 
+    void registerHostProvider(HostProvider provider) {
+        hostProviders.put(provider.id(), provider);
+    }
+
+    void unregisterHostProvider(HostProvider provider) {
+        // TODO find out how to call this
+    }
+
     @Override
     public void run(Timeout timeout) throws Exception {
         for (IpAddress ip : monitoredAddresses) {
-            Set<Host> hosts = Collections.emptySet(); //TODO hostService.getHostsByIp(ip);
+            // TODO have to convert right now because the HostService API uses IpPrefix
+            IpPrefix prefix = IpPrefix.valueOf(ip.toOctets());
+
+            Set<Host> hosts = hostManager.getHostsByIp(prefix);
 
             if (hosts.isEmpty()) {
                 sendArpRequest(ip);
             } else {
                 for (Host host : hosts) {
-                    hostProvider.triggerProbe(host);
+                    HostProvider provider = hostProviders.get(host.providerId());
+                    if (provider != null) {
+                        provider.triggerProbe(host);
+                    }
                 }
             }
         }
@@ -120,29 +137,26 @@
      * @param targetIp IP address to ARP for
      */
     private void sendArpRequest(IpAddress targetIp) {
-
         // Find ports with an IP address in the target's subnet and sent ARP
         // probes out those ports.
         for (Device device : deviceService.getDevices()) {
             for (Port port : deviceService.getPorts(device.id())) {
                 ConnectPoint cp = new ConnectPoint(device.id(), port.number());
-                PortAddresses addresses = hostStore.getAddressBindingsForPort(cp);
+                PortAddresses addresses = hostManager.getAddressBindingsForPort(cp);
 
-                /*for (IpPrefix prefix : addresses.ips()) {
+                for (IpPrefix prefix : addresses.ips()) {
                     if (prefix.contains(targetIp)) {
-                        sendProbe(device.id(), port, addresses, targetIp);
+                        sendProbe(device.id(), port, targetIp,
+                                prefix.toIpAddress(), addresses.mac());
                     }
-                }*/
+                }
             }
         }
-
-        // TODO case where no address was found.
-        // Broadcast out internal edge ports?
     }
 
-    private void sendProbe(DeviceId deviceId, Port port, PortAddresses portAddresses,
-            IpAddress targetIp) {
-        Ethernet arpPacket = createArpFor(targetIp, portAddresses);
+    private void sendProbe(DeviceId deviceId, Port port, IpAddress targetIp,
+            IpAddress sourceIp, MacAddress sourceMac) {
+        Ethernet arpPacket = buildArpRequest(targetIp, sourceIp, sourceMac);
 
         List<Instruction> instructions = new ArrayList<>();
         instructions.add(Instructions.createOutput(port.number()));
@@ -158,31 +172,26 @@
         packetService.emit(outboundPacket);
     }
 
-    private Ethernet createArpFor(IpAddress targetIp, PortAddresses portAddresses) {
+    private Ethernet buildArpRequest(IpAddress targetIp, IpAddress sourceIp,
+            MacAddress sourceMac) {
 
         ARP arp = new ARP();
         arp.setHardwareType(ARP.HW_TYPE_ETHERNET)
-        .setHardwareAddressLength((byte) Ethernet.DATALAYER_ADDRESS_LENGTH)
-        .setProtocolType(ARP.PROTO_TYPE_IP)
-        .setProtocolAddressLength((byte) IpPrefix.INET_LEN);
+           .setHardwareAddressLength((byte) Ethernet.DATALAYER_ADDRESS_LENGTH)
+           .setProtocolType(ARP.PROTO_TYPE_IP)
+           .setProtocolAddressLength((byte) IpPrefix.INET_LEN)
+           .setOpCode(ARP.OP_REQUEST);
 
-        byte[] sourceMacAddress;
-        if (portAddresses.mac() == null) {
-            sourceMacAddress = DEFAULT_MAC_ADDRESS;
-        } else {
-            sourceMacAddress = portAddresses.mac().getAddress();
-        }
-
-        arp.setSenderHardwareAddress(sourceMacAddress)
-        //TODO .setSenderProtocolAddress(portAddresses.ips().toOctets())
-        .setTargetHardwareAddress(ZERO_MAC_ADDRESS)
-        .setTargetProtocolAddress(targetIp.toOctets());
+        arp.setSenderHardwareAddress(sourceMac.getAddress())
+           .setSenderProtocolAddress(sourceIp.toOctets())
+           .setTargetHardwareAddress(ZERO_MAC_ADDRESS)
+           .setTargetProtocolAddress(targetIp.toOctets());
 
         Ethernet ethernet = new Ethernet();
         ethernet.setEtherType(Ethernet.TYPE_ARP)
-        .setDestinationMACAddress(BROADCAST_MAC)
-        .setSourceMACAddress(sourceMacAddress)
-        .setPayload(arp);
+                .setDestinationMACAddress(BROADCAST_MAC)
+                .setSourceMACAddress(sourceMac.getAddress())
+                .setPayload(arp);
 
         return ethernet;
     }
diff --git a/utils/misc/src/main/java/org/onlab/packet/IpPrefix.java b/utils/misc/src/main/java/org/onlab/packet/IpPrefix.java
index b205f90..84acb82 100644
--- a/utils/misc/src/main/java/org/onlab/packet/IpPrefix.java
+++ b/utils/misc/src/main/java/org/onlab/packet/IpPrefix.java
@@ -250,6 +250,17 @@
         return new IpPrefix(version, host, netmask);
     }
 
+    /**
+     * Returns an IpAddress of the bytes contained in this prefix.
+     * FIXME this is a hack for now and only works because IpPrefix doesn't
+     * mask the input bytes on creation.
+     *
+     * @return the IpAddress
+     */
+    public IpAddress toIpAddress() {
+        return IpAddress.valueOf(octets);
+    }
+
     public boolean isMasked() {
         return mask() != 0;
     }
@@ -278,6 +289,17 @@
         return false;
     }
 
+    public boolean contains(IpAddress address) {
+        // Need to get the network address because prefixes aren't automatically
+        // masked on creation
+        IpPrefix meMasked = network();
+
+        IpPrefix otherMasked =
+                IpPrefix.valueOf(address.octets, netmask).network();
+
+        return Arrays.equals(meMasked.octets, otherMasked.octets);
+    }
+
     @Override
     public int hashCode() {
         final int prime = 31;
@@ -303,6 +325,7 @@
         if (netmask != other.netmask) {
             return false;
         }
+        // TODO not quite right until we mask the input
         if (!Arrays.equals(octets, other.octets)) {
             return false;
         }
diff --git a/utils/misc/src/test/java/org/onlab/packet/IpPrefixTest.java b/utils/misc/src/test/java/org/onlab/packet/IpPrefixTest.java
index f6bf6f1..297a0f3 100644
--- a/utils/misc/src/test/java/org/onlab/packet/IpPrefixTest.java
+++ b/utils/misc/src/test/java/org/onlab/packet/IpPrefixTest.java
@@ -76,7 +76,7 @@
     }
 
     @Test
-    public void testContains() {
+    public void testContainsIpPrefix() {
         IpPrefix slash31 = IpPrefix.valueOf(BYTES1, 31);
         IpPrefix slash32 = IpPrefix.valueOf(BYTES1, 32);
         IpPrefix differentSlash32 = IpPrefix.valueOf(BYTES2, 32);
@@ -96,4 +96,17 @@
         assertTrue(slash8.contains(slash31));
         assertFalse(slash31.contains(slash8));
     }
+
+    @Test
+    public void testContainsIpAddress() {
+        IpPrefix slash31 = IpPrefix.valueOf(BYTES1, 31);
+        IpAddress slash32 = IpAddress.valueOf(BYTES1, 32);
+
+        assertTrue(slash31.contains(slash32));
+
+        IpPrefix intf = IpPrefix.valueOf("192.168.10.101/24");
+        IpAddress addr = IpAddress.valueOf("192.168.10.1");
+
+        assertTrue(intf.contains(addr));
+    }
 }