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 8b1e1ce..a99fb53 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
@@ -35,8 +35,11 @@
 import org.onlab.onos.net.DeviceId;
 import org.onlab.onos.net.PortNumber;
 import org.onlab.onos.net.host.HostAdminService;
+import org.onlab.onos.net.host.InterfaceIpAddress;
 import org.onlab.onos.net.host.PortAddresses;
+import org.onlab.packet.IpAddress;
 import org.onlab.packet.IpPrefix;
+import org.onlab.packet.Ip4Prefix;
 import org.onlab.packet.MacAddress;
 import org.slf4j.Logger;
 
@@ -72,12 +75,25 @@
                         DeviceId.deviceId(dpidToUri(entry.getDpid())),
                         PortNumber.portNumber(entry.getPortNumber()));
 
-                Set<IpPrefix> ipAddresses = new HashSet<IpPrefix>();
+                Set<InterfaceIpAddress> interfaceIpAddresses = new HashSet<>();
 
                 for (String strIp : entry.getIpAddresses()) {
+                    // Get the IP address and the subnet mask length
                     try {
-                        IpPrefix address = IpPrefix.valueOf(strIp);
-                        ipAddresses.add(address);
+                        String[] splits = strIp.split("/");
+                        if (splits.length != 2) {
+                            throw new IllegalArgumentException("Invalid IP address and prefix length format");
+                        }
+                        //
+                        // TODO: For now we need Ip4Prefix to mask-out the
+                        // subnet address.
+                        //
+                        Ip4Prefix subnet4 = new Ip4Prefix(strIp);
+                        IpPrefix subnet = IpPrefix.valueOf(subnet4.toString());
+                        IpAddress addr = IpAddress.valueOf(splits[0]);
+                        InterfaceIpAddress ia =
+                            new InterfaceIpAddress(addr, subnet);
+                        interfaceIpAddresses.add(ia);
                     } catch (IllegalArgumentException e) {
                         log.warn("Bad format for IP address in config: {}", strIp);
                     }
@@ -94,7 +110,7 @@
                 }
 
                 PortAddresses addresses = new PortAddresses(cp,
-                        ipAddresses, macAddress);
+                        interfaceIpAddresses, macAddress);
 
                 hostAdminService.bindAddressesToPort(addresses);
             }
diff --git a/apps/sdnip/src/main/java/org/onlab/onos/sdnip/HostToInterfaceAdaptor.java b/apps/sdnip/src/main/java/org/onlab/onos/sdnip/HostToInterfaceAdaptor.java
index 5dc2d1f..a02ce27 100644
--- a/apps/sdnip/src/main/java/org/onlab/onos/sdnip/HostToInterfaceAdaptor.java
+++ b/apps/sdnip/src/main/java/org/onlab/onos/sdnip/HostToInterfaceAdaptor.java
@@ -24,10 +24,10 @@
 
 import org.onlab.onos.net.ConnectPoint;
 import org.onlab.onos.net.host.HostService;
+import org.onlab.onos.net.host.InterfaceIpAddress;
 import org.onlab.onos.net.host.PortAddresses;
 import org.onlab.onos.sdnip.config.Interface;
 import org.onlab.packet.IpAddress;
-import org.onlab.packet.IpPrefix;
 
 import com.google.common.collect.Sets;
 
@@ -59,7 +59,7 @@
         PortAddresses portAddresses =
                 hostService.getAddressBindingsForPort(connectPoint);
 
-        if (!portAddresses.ips().isEmpty()) {
+        if (!portAddresses.ipAddresses().isEmpty()) {
             return new Interface(portAddresses);
         }
 
@@ -71,8 +71,8 @@
         checkNotNull(ipAddress);
 
         for (PortAddresses portAddresses : hostService.getAddressBindings()) {
-            for (IpPrefix p : portAddresses.ips()) {
-                if (p.contains(ipAddress)) {
+            for (InterfaceIpAddress ia : portAddresses.ipAddresses()) {
+                if (ia.subnetAddress().contains(ipAddress)) {
                     return new Interface(portAddresses);
                 }
             }
diff --git a/apps/sdnip/src/main/java/org/onlab/onos/sdnip/config/Interface.java b/apps/sdnip/src/main/java/org/onlab/onos/sdnip/config/Interface.java
index 52c4cde..829cffa 100644
--- a/apps/sdnip/src/main/java/org/onlab/onos/sdnip/config/Interface.java
+++ b/apps/sdnip/src/main/java/org/onlab/onos/sdnip/config/Interface.java
@@ -22,8 +22,8 @@
 import java.util.Set;
 
 import org.onlab.onos.net.ConnectPoint;
+import org.onlab.onos.net.host.InterfaceIpAddress;
 import org.onlab.onos.net.host.PortAddresses;
-import org.onlab.packet.IpPrefix;
 import org.onlab.packet.MacAddress;
 
 import com.google.common.base.MoreObjects;
@@ -35,21 +35,22 @@
  */
 public class Interface {
     private final ConnectPoint connectPoint;
-    private final Set<IpPrefix> ipAddresses;
+    private final Set<InterfaceIpAddress> ipAddresses;
     private final MacAddress macAddress;
 
     /**
-     * Creates an Interface based on a connection point, a set of IP addresses
-     * and a MAC address.
+     * Creates an Interface based on a connection point, a set of interface
+     * IP addresses, and a MAC address.
      *
      * @param connectPoint the connect point this interface is mapped to
-     * @param prefixAddress the IP addresses for the interface
+     * @param ipAddresses the IP addresses for the interface
      * @param macAddress the MAC address of the interface
      */
-    public Interface(ConnectPoint connectPoint, Set<IpPrefix> prefixAddress,
+    public Interface(ConnectPoint connectPoint,
+                     Set<InterfaceIpAddress> ipAddresses,
                      MacAddress macAddress) {
         this.connectPoint = connectPoint;
-        this.ipAddresses = Sets.newHashSet(prefixAddress);
+        this.ipAddresses = Sets.newHashSet(ipAddresses);
         this.macAddress = macAddress;
     }
 
@@ -60,7 +61,7 @@
      */
     public Interface(PortAddresses portAddresses) {
         connectPoint = portAddresses.connectPoint();
-        ipAddresses = Sets.newHashSet(portAddresses.ips());
+        ipAddresses = Sets.newHashSet(portAddresses.ipAddresses());
         macAddress = portAddresses.mac();
     }
 
@@ -76,9 +77,9 @@
     /**
      * Retrieves the set of IP addresses that are assigned to the interface.
      *
-     * @return the set of IP addresses
+     * @return the set of interface IP addresses
      */
-   public Set<IpPrefix> ips() {
+   public Set<InterfaceIpAddress> ipAddresses() {
         return ipAddresses;
     }
 
diff --git a/apps/sdnip/src/test/java/org/onlab/onos/sdnip/HostToInterfaceAdaptorTest.java b/apps/sdnip/src/test/java/org/onlab/onos/sdnip/HostToInterfaceAdaptorTest.java
index e9a8420..a42cd87 100644
--- a/apps/sdnip/src/test/java/org/onlab/onos/sdnip/HostToInterfaceAdaptorTest.java
+++ b/apps/sdnip/src/test/java/org/onlab/onos/sdnip/HostToInterfaceAdaptorTest.java
@@ -35,6 +35,7 @@
 import org.onlab.onos.net.DeviceId;
 import org.onlab.onos.net.PortNumber;
 import org.onlab.onos.net.host.HostService;
+import org.onlab.onos.net.host.InterfaceIpAddress;
 import org.onlab.onos.net.host.PortAddresses;
 import org.onlab.onos.sdnip.config.Interface;
 import org.onlab.packet.IpAddress;
@@ -76,20 +77,33 @@
         portAddresses = Sets.newHashSet();
         interfaces = Maps.newHashMap();
 
+        InterfaceIpAddress ia11 =
+            new InterfaceIpAddress(IpAddress.valueOf("192.168.1.1"),
+                                   IpPrefix.valueOf("192.168.1.0/24"));
         createPortAddressesAndInterface(CP1,
-                Sets.newHashSet(IpPrefix.valueOf("192.168.1.1/24")),
+                Sets.newHashSet(ia11),
                 MacAddress.valueOf("00:00:00:00:00:01"));
 
         // Two addresses in the same subnet
+        InterfaceIpAddress ia21 =
+            new InterfaceIpAddress(IpAddress.valueOf("192.168.2.1"),
+                                   IpPrefix.valueOf("192.168.2.0/24"));
+        InterfaceIpAddress ia22 =
+            new InterfaceIpAddress(IpAddress.valueOf("192.168.2.2"),
+                                   IpPrefix.valueOf("192.168.2.0/24"));
         createPortAddressesAndInterface(CP2,
-                Sets.newHashSet(IpPrefix.valueOf("192.168.2.1/24"),
-                        IpPrefix.valueOf("192.168.2.2/24")),
+                Sets.newHashSet(ia21, ia22),
                 MacAddress.valueOf("00:00:00:00:00:02"));
 
         // Two addresses in different subnets
+        InterfaceIpAddress ia31 =
+            new InterfaceIpAddress(IpAddress.valueOf("192.168.3.1"),
+                                   IpPrefix.valueOf("192.168.3.0/24"));
+        InterfaceIpAddress ia41 =
+            new InterfaceIpAddress(IpAddress.valueOf("192.168.4.1"),
+                                   IpPrefix.valueOf("192.168.4.0/24"));
         createPortAddressesAndInterface(CP3,
-                Sets.newHashSet(IpPrefix.valueOf("192.168.3.1/24"),
-                        IpPrefix.valueOf("192.168.4.1/24")),
+                Sets.newHashSet(ia31, ia41),
                 MacAddress.valueOf("00:00:00:00:00:03"));
 
         expect(hostService.getAddressBindings()).andReturn(portAddresses).anyTimes();
@@ -104,16 +118,17 @@
      * places them in the correct global data stores.
      *
      * @param cp the connect point
-     * @param ips the set of IP addresses
+     * @param ipAddresses the set of interface IP addresses
      * @param mac the MAC address
      */
     private void createPortAddressesAndInterface(
-            ConnectPoint cp, Set<IpPrefix> ips, MacAddress mac) {
-        PortAddresses pa = new PortAddresses(cp, ips, mac);
+            ConnectPoint cp, Set<InterfaceIpAddress> ipAddresses,
+            MacAddress mac) {
+        PortAddresses pa = new PortAddresses(cp, ipAddresses, mac);
         portAddresses.add(pa);
         expect(hostService.getAddressBindingsForPort(cp)).andReturn(pa).anyTimes();
 
-        Interface intf = new Interface(cp, ips, mac);
+        Interface intf = new Interface(cp, ipAddresses, mac);
         interfaces.put(cp, intf);
     }
 
diff --git a/apps/sdnip/src/test/java/org/onlab/onos/sdnip/PeerConnectivityManagerTest.java b/apps/sdnip/src/test/java/org/onlab/onos/sdnip/PeerConnectivityManagerTest.java
index e3e4896..832989f 100644
--- a/apps/sdnip/src/test/java/org/onlab/onos/sdnip/PeerConnectivityManagerTest.java
+++ b/apps/sdnip/src/test/java/org/onlab/onos/sdnip/PeerConnectivityManagerTest.java
@@ -31,6 +31,7 @@
 import org.onlab.onos.net.flow.DefaultTrafficTreatment;
 import org.onlab.onos.net.flow.TrafficSelector;
 import org.onlab.onos.net.flow.TrafficTreatment;
+import org.onlab.onos.net.host.InterfaceIpAddress;
 import org.onlab.onos.net.intent.IntentService;
 import org.onlab.onos.net.intent.PointToPointIntent;
 import org.onlab.onos.sdnip.bgp.BgpConstants;
@@ -175,14 +176,20 @@
         configuredInterfaces = new HashMap<>();
 
         String interfaceSw1Eth1 = "s1-eth1";
+        InterfaceIpAddress ia1 =
+            new InterfaceIpAddress(IpAddress.valueOf("192.168.10.1"),
+                                   IpPrefix.valueOf("192.168.10.0/24"));
         Interface intfsw1eth1 = new Interface(s1Eth1,
-                Collections.singleton(IpPrefix.valueOf("192.168.10.0/24")),
+                Collections.singleton(ia1),
                 MacAddress.valueOf("00:00:00:00:00:01"));
 
         configuredInterfaces.put(interfaceSw1Eth1, intfsw1eth1);
         String interfaceSw2Eth1 = "s2-eth1";
+        InterfaceIpAddress ia2 =
+            new InterfaceIpAddress(IpAddress.valueOf("192.168.20.2"),
+                                   IpPrefix.valueOf("192.168.20.0/24"));
         Interface intfsw2eth1 = new Interface(s2Eth1,
-                Collections.singleton(IpPrefix.valueOf("192.168.20.0/24")),
+                Collections.singleton(ia2),
                 MacAddress.valueOf("00:00:00:00:00:02"));
         configuredInterfaces.put(interfaceSw2Eth1, intfsw2eth1);
 
diff --git a/apps/sdnip/src/test/java/org/onlab/onos/sdnip/RouterTest.java b/apps/sdnip/src/test/java/org/onlab/onos/sdnip/RouterTest.java
index add4f79..6d77a2c 100644
--- a/apps/sdnip/src/test/java/org/onlab/onos/sdnip/RouterTest.java
+++ b/apps/sdnip/src/test/java/org/onlab/onos/sdnip/RouterTest.java
@@ -51,6 +51,7 @@
 import org.onlab.onos.net.flow.TrafficTreatment;
 import org.onlab.onos.net.host.HostListener;
 import org.onlab.onos.net.host.HostService;
+import org.onlab.onos.net.host.InterfaceIpAddress;
 import org.onlab.onos.net.intent.IntentService;
 import org.onlab.onos.net.intent.MultiPointToSinglePointIntent;
 import org.onlab.onos.net.provider.ProviderId;
@@ -150,22 +151,31 @@
 
         Set<Interface> interfaces = Sets.newHashSet();
 
+        InterfaceIpAddress ia1 =
+            new InterfaceIpAddress(IpAddress.valueOf("192.168.10.101"),
+                                   IpPrefix.valueOf("192.168.10.0/24"));
         Interface sw1Eth1 = new Interface(SW1_ETH1,
-                Sets.newHashSet(IpPrefix.valueOf("192.168.10.101/24")),
+                Sets.newHashSet(ia1),
                 MacAddress.valueOf("00:00:00:00:00:01"));
 
         expect(interfaceService.getInterface(SW1_ETH1)).andReturn(sw1Eth1).anyTimes();
         interfaces.add(sw1Eth1);
 
+        InterfaceIpAddress ia2 =
+            new InterfaceIpAddress(IpAddress.valueOf("192.168.20.101"),
+                                   IpPrefix.valueOf("192.168.20.0/24"));
         Interface sw2Eth1 = new Interface(SW2_ETH1,
-                Sets.newHashSet(IpPrefix.valueOf("192.168.20.101/24")),
+                Sets.newHashSet(ia2),
                 MacAddress.valueOf("00:00:00:00:00:02"));
 
         expect(interfaceService.getInterface(SW2_ETH1)).andReturn(sw2Eth1).anyTimes();
         interfaces.add(sw2Eth1);
 
+        InterfaceIpAddress ia3 =
+            new InterfaceIpAddress(IpAddress.valueOf("192.168.30.101"),
+                                   IpPrefix.valueOf("192.168.30.0/24"));
         Interface sw3Eth1 = new Interface(SW3_ETH1,
-                Sets.newHashSet(IpPrefix.valueOf("192.168.30.101/24")),
+                Sets.newHashSet(ia3),
                 MacAddress.valueOf("00:00:00:00:00:03"));
 
         expect(interfaceService.getInterface(SW3_ETH1)).andReturn(sw3Eth1).anyTimes();
diff --git a/core/api/src/main/java/org/onlab/onos/net/host/PortAddresses.java b/core/api/src/main/java/org/onlab/onos/net/host/PortAddresses.java
index 4804daf..b6d1239 100644
--- a/core/api/src/main/java/org/onlab/onos/net/host/PortAddresses.java
+++ b/core/api/src/main/java/org/onlab/onos/net/host/PortAddresses.java
@@ -6,7 +6,6 @@
 import java.util.Set;
 
 import org.onlab.onos.net.ConnectPoint;
-import org.onlab.packet.IpPrefix;
 import org.onlab.packet.MacAddress;
 
 import com.google.common.base.MoreObjects;
@@ -17,24 +16,25 @@
 public class PortAddresses {
 
     private final ConnectPoint connectPoint;
-    // TODO: Should this be IpAddress or IpPrefix?
-    private final Set<IpPrefix> ipAddresses;
+    private final Set<InterfaceIpAddress> ipAddresses;
     private final MacAddress macAddress;
 
     /**
-     * Constructs a PortAddress object for the given connection point, with a
+     * Constructs a PortAddresses object for the given connection point, with a
      * set of IP addresses and a MAC address.
      * <p/>
      * Both address parameters are optional and can be set to null.
      *
      * @param connectPoint the connection point these addresses are for
-     * @param ips a set of IP addresses
+     * @param ipAddresses a set of interface IP addresses
      * @param mac a MAC address
      */
     public PortAddresses(ConnectPoint connectPoint,
-            Set<IpPrefix> ips, MacAddress mac) {
+            Set<InterfaceIpAddress> ipAddresses, MacAddress mac) {
         this.connectPoint = connectPoint;
-        this.ipAddresses = (ips == null) ? Collections.<IpPrefix>emptySet() : new HashSet<>(ips);
+        this.ipAddresses = (ipAddresses == null) ?
+            Collections.<InterfaceIpAddress>emptySet()
+            : new HashSet<>(ipAddresses);
         this.macAddress = mac;
     }
 
@@ -48,11 +48,11 @@
     }
 
     /**
-     * Returns the set of IP addresses.
+     * Returns the set of interface IP addresses.
      *
-     * @return the IP addresses
+     * @return the interface IP addresses
      */
-    public Set<IpPrefix> ips() {
+    public Set<InterfaceIpAddress> ipAddresses() {
         return ipAddresses;
     }
 
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 0b3b2cb..a624c07 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
@@ -22,6 +22,7 @@
 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.InterfaceIpAddress;
 import org.onlab.onos.net.host.PortAddresses;
 import org.onlab.onos.net.packet.DefaultOutboundPacket;
 import org.onlab.onos.net.packet.OutboundPacket;
@@ -161,12 +162,13 @@
         for (Device device : deviceService.getDevices()) {
             for (Port port : deviceService.getPorts(device.id())) {
                 ConnectPoint cp = new ConnectPoint(device.id(), port.number());
-                PortAddresses addresses = hostManager.getAddressBindingsForPort(cp);
+                PortAddresses portAddresses =
+                    hostManager.getAddressBindingsForPort(cp);
 
-                for (IpPrefix prefix : addresses.ips()) {
-                    if (prefix.contains(targetIp)) {
+                for (InterfaceIpAddress ia : portAddresses.ipAddresses()) {
+                    if (ia.subnetAddress().contains(targetIp)) {
                         sendProbe(device.id(), port, targetIp,
-                                prefix.toIpAddress(), addresses.mac());
+                                  ia.ipAddress(), portAddresses.mac());
                     }
                 }
             }
diff --git a/core/net/src/main/java/org/onlab/onos/net/proxyarp/impl/ProxyArpManager.java b/core/net/src/main/java/org/onlab/onos/net/proxyarp/impl/ProxyArpManager.java
index 81f42c8..735c109 100644
--- a/core/net/src/main/java/org/onlab/onos/net/proxyarp/impl/ProxyArpManager.java
+++ b/core/net/src/main/java/org/onlab/onos/net/proxyarp/impl/ProxyArpManager.java
@@ -5,7 +5,6 @@
 import static org.slf4j.LoggerFactory.getLogger;
 
 import java.nio.ByteBuffer;
-import java.util.Collections;
 import java.util.List;
 import java.util.Map.Entry;
 import java.util.Set;
@@ -29,6 +28,7 @@
 import org.onlab.onos.net.flow.DefaultTrafficTreatment;
 import org.onlab.onos.net.flow.TrafficTreatment;
 import org.onlab.onos.net.host.HostService;
+import org.onlab.onos.net.host.InterfaceIpAddress;
 import org.onlab.onos.net.host.PortAddresses;
 import org.onlab.onos.net.link.LinkEvent;
 import org.onlab.onos.net.link.LinkListener;
@@ -114,35 +114,37 @@
         checkArgument(arp.getOpCode() == ARP.OP_REQUEST, NOT_ARP_REQUEST);
         checkNotNull(inPort);
 
-        // If the source address matches one of our external addresses
-        // it could be a request from an internal host to an external
-        // address. Forward it over to the correct port.
-        IpAddress source = IpAddress.valueOf(arp.getSenderProtocolAddress());
-        PortAddresses sourceAddresses = findOutsidePortInSubnet(source);
-        if (sourceAddresses != null && !isOutsidePort(inPort)) {
-            for (IpPrefix subnet : sourceAddresses.ips()) {
-                if (subnet.toIpAddress().equals(source)) {
-                    sendTo(eth, sourceAddresses.connectPoint());
-                    return;
-                }
-            }
-        }
-
         // If the request came from outside the network, only reply if it was
         // for one of our external addresses.
         if (isOutsidePort(inPort)) {
-            IpAddress target = IpAddress.valueOf(arp.getTargetProtocolAddress());
-            PortAddresses addresses = hostService.getAddressBindingsForPort(inPort);
+            IpAddress target =
+                IpAddress.valueOf(arp.getTargetProtocolAddress());
+            PortAddresses addresses =
+                hostService.getAddressBindingsForPort(inPort);
 
-            for (IpPrefix interfaceAddress : addresses.ips()) {
-                if (interfaceAddress.toIpAddress().equals(target)) {
-                    Ethernet arpReply = buildArpReply(interfaceAddress,
-                            addresses.mac(), eth);
+            for (InterfaceIpAddress ia : addresses.ipAddresses()) {
+                if (ia.ipAddress().equals(target)) {
+                    Ethernet arpReply =
+                        buildArpReply(ia.ipAddress(), addresses.mac(), eth);
                     sendTo(arpReply, inPort);
                 }
             }
-
             return;
+        } else {
+            // If the source address matches one of our external addresses
+            // it could be a request from an internal host to an external
+            // address. Forward it over to the correct port.
+            IpAddress source =
+                IpAddress.valueOf(arp.getSenderProtocolAddress());
+            PortAddresses sourceAddresses = findPortInSubnet(source);
+            if (sourceAddresses != null) {
+                for (InterfaceIpAddress ia : sourceAddresses.ipAddresses()) {
+                    if (ia.ipAddress().equals(source)) {
+                        sendTo(eth, sourceAddresses.connectPoint());
+                        return;
+                    }
+                }
+            }
         }
 
         // Continue with normal proxy ARP case
@@ -168,8 +170,9 @@
         }
 
         // TODO find the correct IP address
-        Ethernet arpReply = buildArpReply(dst.ipAddresses().iterator().next(),
-                dst.mac(), eth);
+        IpAddress ipAddress =
+            dst.ipAddresses().iterator().next().toIpAddress();
+        Ethernet arpReply = buildArpReply(ipAddress, dst.mac(), eth);
         // TODO: check send status with host service.
         sendTo(arpReply, src.location());
     }
@@ -199,16 +202,14 @@
      * Finds the port with an address in the subnet of the target address, if
      * one exists.
      *
-     * @param target the target address to find a matching external port for
-     * @return a PortAddresses object containing the external addresses if one
-     * was found, otherwise null.
+     * @param target the target address to find a matching port for
+     * @return a PortAddresses object if one was found, otherwise null
      */
-    private PortAddresses findOutsidePortInSubnet(IpAddress target) {
+    private PortAddresses findPortInSubnet(IpAddress target) {
         for (PortAddresses addresses : hostService.getAddressBindings()) {
-            for (IpPrefix prefix : addresses.ips()) {
-                if (prefix.contains(target)) {
-                    return new PortAddresses(addresses.connectPoint(),
-                            Collections.singleton(prefix), addresses.mac());
+            for (InterfaceIpAddress ia : addresses.ipAddresses()) {
+                if (ia.subnetAddress().contains(target)) {
+                    return addresses;
                 }
             }
         }
@@ -223,7 +224,11 @@
      * @return true if the port is an outside-facing port, otherwise false
      */
     private boolean isOutsidePort(ConnectPoint port) {
-        return !hostService.getAddressBindingsForPort(port).ips().isEmpty();
+        //
+        // TODO: Is this sufficient to identify outside-facing ports: just
+        // having IP addresses on a port?
+        //
+        return !hostService.getAddressBindingsForPort(port).ipAddresses().isEmpty();
     }
 
     @Override
@@ -335,7 +340,7 @@
      * @param request the ARP request we got
      * @return an Ethernet frame containing the ARP reply
      */
-    private Ethernet buildArpReply(IpPrefix srcIp, MacAddress srcMac,
+    private Ethernet buildArpReply(IpAddress srcIp, MacAddress srcMac,
             Ethernet request) {
 
         Ethernet eth = new Ethernet();
diff --git a/core/net/src/test/java/org/onlab/onos/net/host/impl/HostManagerTest.java b/core/net/src/test/java/org/onlab/onos/net/host/impl/HostManagerTest.java
index 6864fd7..c20da19 100644
--- a/core/net/src/test/java/org/onlab/onos/net/host/impl/HostManagerTest.java
+++ b/core/net/src/test/java/org/onlab/onos/net/host/impl/HostManagerTest.java
@@ -31,10 +31,12 @@
 import org.onlab.onos.net.host.HostProvider;
 import org.onlab.onos.net.host.HostProviderRegistry;
 import org.onlab.onos.net.host.HostProviderService;
+import org.onlab.onos.net.host.InterfaceIpAddress;
 import org.onlab.onos.net.host.PortAddresses;
 import org.onlab.onos.net.provider.AbstractProvider;
 import org.onlab.onos.net.provider.ProviderId;
 import org.onlab.onos.store.trivial.impl.SimpleHostStore;
+import org.onlab.packet.IpAddress;
 import org.onlab.packet.IpPrefix;
 import org.onlab.packet.MacAddress;
 import org.onlab.packet.VlanId;
@@ -68,9 +70,15 @@
     private static final ConnectPoint CP1 = new ConnectPoint(DID1, P1);
     private static final ConnectPoint CP2 = new ConnectPoint(DID2, P2);
 
-    private static final IpPrefix PREFIX1 = IpPrefix.valueOf("10.0.1.0/24");
-    private static final IpPrefix PREFIX2 = IpPrefix.valueOf("10.1.0.0/16");
-    private static final IpPrefix PREFIX3 = IpPrefix.valueOf("5.8.2.0/23");
+    private static final InterfaceIpAddress IA1 =
+        new InterfaceIpAddress(IpAddress.valueOf("10.1.1.1"),
+                               IpPrefix.valueOf("10.1.1.0/24"));
+    private static final InterfaceIpAddress IA2 =
+        new InterfaceIpAddress(IpAddress.valueOf("10.2.2.2"),
+                               IpPrefix.valueOf("10.2.0.0/16"));
+    private static final InterfaceIpAddress IA3 =
+        new InterfaceIpAddress(IpAddress.valueOf("10.3.3.3"),
+                               IpPrefix.valueOf("10.3.3.0/24"));
 
     private HostManager mgr;
 
@@ -207,23 +215,24 @@
 
     @Test
     public void bindAddressesToPort() {
-        PortAddresses add1 = new PortAddresses(CP1,
-                                               Sets.newHashSet(PREFIX1, PREFIX2), MAC1);
+        PortAddresses add1 =
+            new PortAddresses(CP1, Sets.newHashSet(IA1, IA2), MAC1);
 
         mgr.bindAddressesToPort(add1);
         PortAddresses storedAddresses = mgr.getAddressBindingsForPort(CP1);
 
-        assertTrue(add1.ips().equals(storedAddresses.ips()));
+        assertTrue(add1.ipAddresses().equals(storedAddresses.ipAddresses()));
         assertTrue(add1.mac().equals(storedAddresses.mac()));
 
         // Add some more addresses and check that they're added correctly
-        PortAddresses add2 = new PortAddresses(CP1, Sets.newHashSet(PREFIX3), null);
+        PortAddresses add2 =
+            new PortAddresses(CP1, Sets.newHashSet(IA3),  null);
 
         mgr.bindAddressesToPort(add2);
         storedAddresses = mgr.getAddressBindingsForPort(CP1);
 
-        assertTrue(storedAddresses.ips().equals(
-                Sets.newHashSet(PREFIX1, PREFIX2, PREFIX3)));
+        assertTrue(storedAddresses.ipAddresses().equals(
+                Sets.newHashSet(IA1, IA2, IA3)));
         assertTrue(storedAddresses.mac().equals(MAC1));
 
         PortAddresses add3 = new PortAddresses(CP1, null, MAC2);
@@ -231,29 +240,29 @@
         mgr.bindAddressesToPort(add3);
         storedAddresses = mgr.getAddressBindingsForPort(CP1);
 
-        assertTrue(storedAddresses.ips().equals(
-                Sets.newHashSet(PREFIX1, PREFIX2, PREFIX3)));
+        assertTrue(storedAddresses.ipAddresses().equals(
+                Sets.newHashSet(IA1, IA2, IA3)));
         assertTrue(storedAddresses.mac().equals(MAC2));
     }
 
     @Test
     public void unbindAddressesFromPort() {
-        PortAddresses add1 = new PortAddresses(CP1,
-                                               Sets.newHashSet(PREFIX1, PREFIX2), MAC1);
+        PortAddresses add1 =
+            new PortAddresses(CP1, Sets.newHashSet(IA1, IA2), MAC1);
 
         mgr.bindAddressesToPort(add1);
         PortAddresses storedAddresses = mgr.getAddressBindingsForPort(CP1);
 
-        assertTrue(storedAddresses.ips().size() == 2);
+        assertTrue(storedAddresses.ipAddresses().size() == 2);
         assertNotNull(storedAddresses.mac());
 
-        PortAddresses rem1 = new PortAddresses(CP1,
-                                               Sets.newHashSet(PREFIX1), null);
+        PortAddresses rem1 =
+            new PortAddresses(CP1, Sets.newHashSet(IA1), null);
 
         mgr.unbindAddressesFromPort(rem1);
         storedAddresses = mgr.getAddressBindingsForPort(CP1);
 
-        assertTrue(storedAddresses.ips().equals(Sets.newHashSet(PREFIX2)));
+        assertTrue(storedAddresses.ipAddresses().equals(Sets.newHashSet(IA2)));
         assertTrue(storedAddresses.mac().equals(MAC1));
 
         PortAddresses rem2 = new PortAddresses(CP1, null, MAC1);
@@ -261,47 +270,48 @@
         mgr.unbindAddressesFromPort(rem2);
         storedAddresses = mgr.getAddressBindingsForPort(CP1);
 
-        assertTrue(storedAddresses.ips().equals(Sets.newHashSet(PREFIX2)));
+        assertTrue(storedAddresses.ipAddresses().equals(Sets.newHashSet(IA2)));
         assertNull(storedAddresses.mac());
 
-        PortAddresses rem3 = new PortAddresses(CP1,
-                                               Sets.newHashSet(PREFIX2), MAC1);
+        PortAddresses rem3 =
+            new PortAddresses(CP1, Sets.newHashSet(IA2), MAC1);
 
         mgr.unbindAddressesFromPort(rem3);
         storedAddresses = mgr.getAddressBindingsForPort(CP1);
 
-        assertTrue(storedAddresses.ips().isEmpty());
+        assertTrue(storedAddresses.ipAddresses().isEmpty());
         assertNull(storedAddresses.mac());
     }
 
     @Test
     public void clearAddresses() {
-        PortAddresses add1 = new PortAddresses(CP1,
-                                               Sets.newHashSet(PREFIX1, PREFIX2), MAC1);
+        PortAddresses add1 =
+            new PortAddresses(CP1, Sets.newHashSet(IA1, IA2), MAC1);
 
         mgr.bindAddressesToPort(add1);
         PortAddresses storedAddresses = mgr.getAddressBindingsForPort(CP1);
 
-        assertTrue(storedAddresses.ips().size() == 2);
+        assertTrue(storedAddresses.ipAddresses().size() == 2);
         assertNotNull(storedAddresses.mac());
 
         mgr.clearAddresses(CP1);
         storedAddresses = mgr.getAddressBindingsForPort(CP1);
 
-        assertTrue(storedAddresses.ips().isEmpty());
+        assertTrue(storedAddresses.ipAddresses().isEmpty());
         assertNull(storedAddresses.mac());
     }
 
     @Test
     public void getAddressBindingsForPort() {
-        PortAddresses add1 = new PortAddresses(CP1,
-                                               Sets.newHashSet(PREFIX1, PREFIX2), MAC1);
+        PortAddresses add1 =
+            new PortAddresses(CP1, Sets.newHashSet(IA1, IA2), MAC1);
 
         mgr.bindAddressesToPort(add1);
         PortAddresses storedAddresses = mgr.getAddressBindingsForPort(CP1);
 
         assertTrue(storedAddresses.connectPoint().equals(CP1));
-        assertTrue(storedAddresses.ips().equals(Sets.newHashSet(PREFIX1, PREFIX2)));
+        assertTrue(storedAddresses.ipAddresses().equals(
+                        Sets.newHashSet(IA1, IA2)));
         assertTrue(storedAddresses.mac().equals(MAC1));
     }
 
@@ -311,8 +321,8 @@
 
         assertTrue(storedAddresses.isEmpty());
 
-        PortAddresses add1 = new PortAddresses(CP1,
-                                               Sets.newHashSet(PREFIX1, PREFIX2), MAC1);
+        PortAddresses add1 =
+            new PortAddresses(CP1, Sets.newHashSet(IA1, IA2), MAC1);
 
         mgr.bindAddressesToPort(add1);
 
@@ -320,8 +330,8 @@
 
         assertTrue(storedAddresses.size() == 1);
 
-        PortAddresses add2 = new PortAddresses(CP2,
-                                               Sets.newHashSet(PREFIX3), MAC2);
+        PortAddresses add2 =
+            new PortAddresses(CP2, Sets.newHashSet(IA3), MAC2);
 
         mgr.bindAddressesToPort(add2);
 
diff --git a/core/net/src/test/java/org/onlab/onos/net/host/impl/HostMonitorTest.java b/core/net/src/test/java/org/onlab/onos/net/host/impl/HostMonitorTest.java
index 7fc6b8c..4b9d214 100644
--- a/core/net/src/test/java/org/onlab/onos/net/host/impl/HostMonitorTest.java
+++ b/core/net/src/test/java/org/onlab/onos/net/host/impl/HostMonitorTest.java
@@ -28,6 +28,7 @@
 import org.onlab.onos.net.flow.instructions.Instruction;
 import org.onlab.onos.net.flow.instructions.Instructions.OutputInstruction;
 import org.onlab.onos.net.host.HostProvider;
+import org.onlab.onos.net.host.InterfaceIpAddress;
 import org.onlab.onos.net.host.PortAddresses;
 import org.onlab.onos.net.packet.OutboundPacket;
 import org.onlab.onos.net.packet.PacketProcessor;
@@ -48,7 +49,10 @@
     private IpAddress targetIpAddress = IpAddress.valueOf("10.0.0.1");
     private IpPrefix targetIpPrefix = IpPrefix.valueOf(targetIpAddress.toOctets());
 
-    private IpPrefix sourcePrefix = IpPrefix.valueOf("10.0.0.99/24");
+    private static final IpAddress SOURCE_ADDR =
+        IpAddress.valueOf("10.0.0.99");
+    private static final InterfaceIpAddress IA1 =
+        new InterfaceIpAddress(SOURCE_ADDR, IpPrefix.valueOf("10.0.0.0/24"));
     private MacAddress sourceMac = MacAddress.valueOf(1L);
 
     private HostMonitor hostMonitor;
@@ -108,8 +112,8 @@
         deviceService.addDevice(device, Collections.singleton(port));
 
         ConnectPoint cp = new ConnectPoint(devId, portNum);
-        PortAddresses pa = new PortAddresses(cp, Collections.singleton(sourcePrefix),
-                sourceMac);
+        PortAddresses pa =
+            new PortAddresses(cp, Collections.singleton(IA1), sourceMac);
 
         expect(hostManager.getHostsByIp(targetIpPrefix))
                 .andReturn(Collections.<Host>emptySet()).anyTimes();
@@ -143,7 +147,8 @@
         Ethernet eth = new Ethernet();
         eth.deserialize(packet.data().array(), 0, packet.data().array().length);
         ARP arp = (ARP) eth.getPayload();
-        assertTrue(Arrays.equals(arp.getSenderProtocolAddress(), sourcePrefix.toOctets()));
+        assertTrue(Arrays.equals(arp.getSenderProtocolAddress(),
+                                 SOURCE_ADDR.toOctets()));
         assertTrue(Arrays.equals(arp.getSenderHardwareAddress(), sourceMac.toBytes()));
         assertTrue(Arrays.equals(arp.getTargetProtocolAddress(), targetIpPrefix.toOctets()));
     }
diff --git a/core/net/src/test/java/org/onlab/onos/net/proxyarp/impl/ProxyArpManagerTest.java b/core/net/src/test/java/org/onlab/onos/net/proxyarp/impl/ProxyArpManagerTest.java
index fa68761..76bf021 100644
--- a/core/net/src/test/java/org/onlab/onos/net/proxyarp/impl/ProxyArpManagerTest.java
+++ b/core/net/src/test/java/org/onlab/onos/net/proxyarp/impl/ProxyArpManagerTest.java
@@ -32,6 +32,7 @@
 import org.onlab.onos.net.flow.instructions.Instruction;
 import org.onlab.onos.net.flow.instructions.Instructions.OutputInstruction;
 import org.onlab.onos.net.host.HostService;
+import org.onlab.onos.net.host.InterfaceIpAddress;
 import org.onlab.onos.net.host.PortAddresses;
 import org.onlab.onos.net.link.LinkListener;
 import org.onlab.onos.net.link.LinkService;
@@ -41,6 +42,7 @@
 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.packet.VlanId;
@@ -186,10 +188,15 @@
 
         for (int i = 1; i <= NUM_ADDRESS_PORTS; i++) {
             ConnectPoint cp = new ConnectPoint(getDeviceId(i), P1);
-            IpPrefix prefix1 = IpPrefix.valueOf("10.0." + (2 * i - 1) + ".1/24");
-            IpPrefix prefix2 = IpPrefix.valueOf("10.0." + (2 * i) + ".1/24");
-            PortAddresses pa = new PortAddresses(cp,
-                    Sets.newHashSet(prefix1, prefix2), MacAddress.valueOf(i));
+            IpPrefix prefix1 = IpPrefix.valueOf("10.0." + (2 * i - 1) + ".0/24");
+            IpAddress addr1 = IpAddress.valueOf("10.0." + (2 * i - 1) + ".1");
+            IpPrefix prefix2 = IpPrefix.valueOf("10.0." + (2 * i) + ".0/24");
+            IpAddress addr2 = IpAddress.valueOf("10.0." + (2 * i) + ".1");
+            InterfaceIpAddress ia1 = new InterfaceIpAddress(addr1, prefix1);
+            InterfaceIpAddress ia2 = new InterfaceIpAddress(addr2, prefix2);
+            PortAddresses pa =
+                new PortAddresses(cp, Sets.newHashSet(ia1, ia2),
+                                  MacAddress.valueOf(i));
             addresses.add(pa);
 
             expect(hostService.getAddressBindingsForPort(cp))
diff --git a/core/store/dist/src/main/java/org/onlab/onos/store/host/impl/GossipHostStore.java b/core/store/dist/src/main/java/org/onlab/onos/store/host/impl/GossipHostStore.java
index ee3fb45..e3e35bc 100644
--- a/core/store/dist/src/main/java/org/onlab/onos/store/host/impl/GossipHostStore.java
+++ b/core/store/dist/src/main/java/org/onlab/onos/store/host/impl/GossipHostStore.java
@@ -30,6 +30,7 @@
 import org.onlab.onos.net.host.HostEvent;
 import org.onlab.onos.net.host.HostStore;
 import org.onlab.onos.net.host.HostStoreDelegate;
+import org.onlab.onos.net.host.InterfaceIpAddress;
 import org.onlab.onos.net.host.PortAddresses;
 import org.onlab.onos.net.provider.ProviderId;
 import org.onlab.onos.store.AbstractStore;
@@ -332,8 +333,9 @@
             if (existing == null) {
                 portAddresses.put(addresses.connectPoint(), addresses);
             } else {
-                Set<IpPrefix> union = Sets.union(existing.ips(), addresses.ips())
-                        .immutableCopy();
+                Set<InterfaceIpAddress> union =
+                    Sets.union(existing.ipAddresses(),
+                               addresses.ipAddresses()).immutableCopy();
 
                 MacAddress newMac = (addresses.mac() == null) ? existing.mac()
                         : addresses.mac();
@@ -351,8 +353,9 @@
         synchronized (portAddresses) {
             PortAddresses existing = portAddresses.get(addresses.connectPoint());
             if (existing != null) {
-                Set<IpPrefix> difference =
-                        Sets.difference(existing.ips(), addresses.ips()).immutableCopy();
+                Set<InterfaceIpAddress> difference =
+                    Sets.difference(existing.ipAddresses(),
+                                    addresses.ipAddresses()).immutableCopy();
 
                 // If they removed the existing mac, set the new mac to null.
                 // Otherwise, keep the existing mac.
diff --git a/core/store/trivial/src/main/java/org/onlab/onos/store/trivial/impl/SimpleHostStore.java b/core/store/trivial/src/main/java/org/onlab/onos/store/trivial/impl/SimpleHostStore.java
index ee8570d..f28e656 100644
--- a/core/store/trivial/src/main/java/org/onlab/onos/store/trivial/impl/SimpleHostStore.java
+++ b/core/store/trivial/src/main/java/org/onlab/onos/store/trivial/impl/SimpleHostStore.java
@@ -19,6 +19,7 @@
 import org.onlab.onos.net.host.HostEvent;
 import org.onlab.onos.net.host.HostStore;
 import org.onlab.onos.net.host.HostStoreDelegate;
+import org.onlab.onos.net.host.InterfaceIpAddress;
 import org.onlab.onos.net.host.PortAddresses;
 import org.onlab.onos.net.provider.ProviderId;
 import org.onlab.onos.store.AbstractStore;
@@ -202,8 +203,9 @@
             if (existing == null) {
                 portAddresses.put(addresses.connectPoint(), addresses);
             } else {
-                Set<IpPrefix> union = Sets.union(existing.ips(), addresses.ips())
-                        .immutableCopy();
+                Set<InterfaceIpAddress> union =
+                    Sets.union(existing.ipAddresses(),
+                               addresses.ipAddresses()).immutableCopy();
 
                 MacAddress newMac = (addresses.mac() == null) ? existing.mac()
                         : addresses.mac();
@@ -221,8 +223,9 @@
         synchronized (portAddresses) {
             PortAddresses existing = portAddresses.get(addresses.connectPoint());
             if (existing != null) {
-                Set<IpPrefix> difference =
-                        Sets.difference(existing.ips(), addresses.ips()).immutableCopy();
+                Set<InterfaceIpAddress> difference =
+                        Sets.difference(existing.ipAddresses(),
+                                        addresses.ipAddresses()).immutableCopy();
 
                 // If they removed the existing mac, set the new mac to null.
                 // Otherwise, keep the existing mac.