diff --git a/apps/dhcp/src/main/java/org/onosproject/dhcp/impl/DhcpConfig.java b/apps/dhcp/src/main/java/org/onosproject/dhcp/impl/DhcpConfig.java
index 85ea47b..4353d62 100644
--- a/apps/dhcp/src/main/java/org/onosproject/dhcp/impl/DhcpConfig.java
+++ b/apps/dhcp/src/main/java/org/onosproject/dhcp/impl/DhcpConfig.java
@@ -41,6 +41,8 @@
     public static final String START_IP = "startip";
     public static final String END_IP = "endip";
 
+    public static final int DEFAULT = -1;
+
     /**
      * Returns the dhcp server ip.
      *
@@ -124,10 +126,10 @@
     /**
      * Returns the Time To Live for the reply packets.
      *
-     * @return ttl or null if not set
+     * @return ttl or -1 if not set
      */
     public int ttl() {
-        return get(TTL, 0);
+        return get(TTL, DEFAULT);
     }
 
     /**
@@ -143,10 +145,10 @@
     /**
      * Returns the Lease Time offered by the DHCP Server.
      *
-     * @return lease time or null if not set
+     * @return lease time or -1 if not set
      */
     public int leaseTime() {
-        return get(LEASE_TIME, 0);
+        return get(LEASE_TIME, DEFAULT);
     }
 
     /**
@@ -162,10 +164,10 @@
     /**
      * Returns the Renew Time offered by the DHCP Server.
      *
-     * @return renew time or null if not set
+     * @return renew time or -1 if not set
      */
     public int renewTime() {
-        return get(RENEW_TIME, 0);
+        return get(RENEW_TIME, DEFAULT);
     }
 
     /**
@@ -181,10 +183,10 @@
     /**
      * Returns the Rebind Time offered by the DHCP Server.
      *
-     * @return rebind time or null if not set
+     * @return rebind time or -1 if not set
      */
     public int rebindTime() {
-        return get(REBIND_TIME, 0);
+        return get(REBIND_TIME, DEFAULT);
     }
 
     /**
@@ -238,12 +240,12 @@
     }
 
     /**
-     * Returns the delay after which the dhcp server will purge expired entries.
+     * Returns the delay in minutes after which the dhcp server will purge expired entries.
      *
-     * @return time delay or null if not set
+     * @return time delay or -1 if not set
      */
     public int timerDelay() {
-        return get(TIMER_DELAY, 0);
+        return get(TIMER_DELAY, DEFAULT);
     }
 
     /**
@@ -259,10 +261,10 @@
     /**
      * Returns the default timeout for pending assignments.
      *
-     * @return default timeout or null if not set
+     * @return default timeout or -1 if not set
      */
     public int defaultTimeout() {
-        return get(DEFAULT_TIMEOUT, 0);
+        return get(DEFAULT_TIMEOUT, DEFAULT);
     }
 
     /**
diff --git a/apps/dhcp/src/main/java/org/onosproject/dhcp/impl/DhcpManager.java b/apps/dhcp/src/main/java/org/onosproject/dhcp/impl/DhcpManager.java
index f3f2cee..e3a4f43 100644
--- a/apps/dhcp/src/main/java/org/onosproject/dhcp/impl/DhcpManager.java
+++ b/apps/dhcp/src/main/java/org/onosproject/dhcp/impl/DhcpManager.java
@@ -74,6 +74,7 @@
 import java.util.HashSet;
 import java.util.List;
 import java.util.Map;
+import java.util.Objects;
 import java.util.Set;
 import java.util.concurrent.TimeUnit;
 
@@ -559,7 +560,7 @@
                 ARP arpPacket = (ARP) packet.getPayload();
 
                 if ((arpPacket.getOpCode() == ARP.OP_REQUEST) &&
-                        (myIP).equals(Ip4Address.valueOf(arpPacket.getTargetProtocolAddress()))) {
+                        Objects.equals(myIP, Ip4Address.valueOf(arpPacket.getTargetProtocolAddress()))) {
 
                     processARPPacket(context, packet);
 
@@ -597,22 +598,22 @@
             if (cfg.domainServer() != null) {
                 domainServer = cfg.domainServer();
             }
-            if (cfg.ttl() != 0) {
+            if (cfg.ttl() != -1) {
                 packetTTL = (byte) cfg.ttl();
             }
-            if (cfg.leaseTime() != 0) {
+            if (cfg.leaseTime() != -1) {
                 leaseTime = cfg.leaseTime();
             }
-            if (cfg.renewTime() != 0) {
+            if (cfg.renewTime() != -1) {
                 renewalTime = cfg.renewTime();
             }
-            if (cfg.rebindTime() != 0) {
+            if (cfg.rebindTime() != -1) {
                 rebindingTime = cfg.rebindTime();
             }
-            if (cfg.defaultTimeout() != 0) {
+            if (cfg.defaultTimeout() != -1) {
                 dhcpStore.setDefaultTimeoutForPurge(cfg.defaultTimeout());
             }
-            if (cfg.timerDelay() != 0) {
+            if (cfg.timerDelay() != -1) {
                 timerDelay = cfg.timerDelay();
             }
             if ((cfg.startIp() != null) && (cfg.endIp() != null)) {