diff --git a/apps/dhcprelay/src/main/java/org/onosproject/dhcprelay/Dhcp4HandlerImpl.java b/apps/dhcprelay/src/main/java/org/onosproject/dhcprelay/Dhcp4HandlerImpl.java
index deeaa36..4d2bebb 100644
--- a/apps/dhcprelay/src/main/java/org/onosproject/dhcprelay/Dhcp4HandlerImpl.java
+++ b/apps/dhcprelay/src/main/java/org/onosproject/dhcprelay/Dhcp4HandlerImpl.java
@@ -675,23 +675,24 @@
      * @return true if the host is directly connected to the network; false otherwise
      */
     private boolean directlyConnected(DHCP dhcpPayload) {
-        DhcpOption relayAgentOption = dhcpPayload.getOption(OptionCode_CircuitID);
+        DhcpRelayAgentOption relayAgentOption =
+                (DhcpRelayAgentOption) dhcpPayload.getOption(OptionCode_CircuitID);
 
         // Doesn't contains relay option
         if (relayAgentOption == null) {
             return true;
         }
 
-        IpAddress gatewayIp = IpAddress.valueOf(dhcpPayload.getGatewayIPAddress());
-        Set<Interface> gatewayInterfaces = interfaceService.getInterfacesByIp(gatewayIp);
+        // check circuit id, if circuit id is invalid, we say it is an indirect host
+        DhcpOption circuitIdOpt = relayAgentOption.getSubOption(CIRCUIT_ID.getValue());
 
-        // Contains relay option, and added by ONOS
-        if (!gatewayInterfaces.isEmpty()) {
+        try {
+            CircuitId.deserialize(circuitIdOpt.getData());
             return true;
+        } catch (Exception e) {
+            // invalid circuit id
+            return false;
         }
-
-        // Relay option added by other relay agent
-        return false;
     }
 
 
diff --git a/apps/dhcprelay/src/test/java/org/onosproject/dhcprelay/DhcpRelayManagerTest.java b/apps/dhcprelay/src/test/java/org/onosproject/dhcprelay/DhcpRelayManagerTest.java
index 8a47cf8..71b3cef 100644
--- a/apps/dhcprelay/src/test/java/org/onosproject/dhcprelay/DhcpRelayManagerTest.java
+++ b/apps/dhcprelay/src/test/java/org/onosproject/dhcprelay/DhcpRelayManagerTest.java
@@ -20,6 +20,7 @@
 import com.google.common.collect.Lists;
 import com.google.common.collect.Maps;
 import com.google.common.collect.Sets;
+import org.apache.commons.io.Charsets;
 import org.easymock.EasyMock;
 import org.junit.After;
 import org.junit.Before;
@@ -159,6 +160,7 @@
             CLIENT2_INTERFACE,
             SERVER_INTERFACE
     );
+    private static final String NON_ONOS_CID = "Non-ONOS circuit ID";
 
     private DhcpRelayManager manager;
     private MockPacketService packetService;
@@ -576,8 +578,8 @@
             if (withNonOnosRelayInfo) {
                 DhcpRelayAgentOption relayOption = new DhcpRelayAgentOption();
                 DhcpOption circuitIdOption = new DhcpOption();
-                CircuitId circuitId = new CircuitId("Custom cid", VlanId.NONE);
-                byte[] cid = circuitId.serialize();
+                String circuitId = NON_ONOS_CID;
+                byte[] cid = circuitId.getBytes(Charsets.US_ASCII);
                 circuitIdOption.setCode(DhcpRelayAgentOption.RelayAgentInfoOptions.CIRCUIT_ID.getValue());
                 circuitIdOption.setLength((byte) cid.length);
                 circuitIdOption.setData(cid);
diff --git a/utils/misc/src/main/java/org/onlab/packet/dhcp/CircuitId.java b/utils/misc/src/main/java/org/onlab/packet/dhcp/CircuitId.java
index 3b819e1..1b53a5b 100644
--- a/utils/misc/src/main/java/org/onlab/packet/dhcp/CircuitId.java
+++ b/utils/misc/src/main/java/org/onlab/packet/dhcp/CircuitId.java
@@ -17,6 +17,7 @@
 package org.onlab.packet.dhcp;
 
 import com.google.common.collect.Lists;
+import com.google.common.primitives.UnsignedLongs;
 import org.onlab.packet.VlanId;
 
 import java.nio.charset.StandardCharsets;
@@ -31,6 +32,7 @@
 public class CircuitId {
     private static final String SEPARATOR = ":";
     private static final String CIRCUIT_ID_FORMAT = "%s" + SEPARATOR + "%s";
+    private static final String DEVICE_PORT_SEPARATOR = "/";
     private String connectPoint;
     private VlanId vlanId;
 
@@ -65,11 +67,22 @@
      */
     public static CircuitId deserialize(byte[] circuitId) {
         String cIdString = new String(circuitId, StandardCharsets.US_ASCII);
-        List<String> split = Lists.newArrayList(cIdString.split(SEPARATOR));
-        checkArgument(split.size() > 1, "Illegal circuit id.");
+        List<String> splittedCircuitId = Lists.newArrayList(cIdString.split(SEPARATOR));
+        checkArgument(splittedCircuitId.size() > 1, "Illegal circuit id.");
         // remove last element (vlan id)
-        String vlanId = split.remove(split.size() - 1);
-        String connectPoint = String.join(SEPARATOR, split);
+        String vlanId = splittedCircuitId.remove(splittedCircuitId.size() - 1);
+
+        // Reconstruct device Id
+        String connectPoint = String.join(SEPARATOR, splittedCircuitId);
+
+        String[] splittedConnectPoint = connectPoint.split(DEVICE_PORT_SEPARATOR);
+        // Check connect point is valid or not
+        checkArgument(splittedConnectPoint.length == 2,
+                      "Connect point must be in \"deviceUri/portNumber\" format");
+
+        // Check the port number is a number or not
+        UnsignedLongs.decode(splittedConnectPoint[1]);
+
         return new CircuitId(connectPoint, VlanId.vlanId(vlanId));
     }