diff --git a/src/network.py b/src/network.py
index b4c279a..2d5f15f 100755
--- a/src/network.py
+++ b/src/network.py
@@ -108,10 +108,38 @@ class IntervalPool(object):
             #self.pool[str(i)].sort(key=ip_to_int)  # cidr between thiscidr and upcidr are null, no need to sort
         return [True, upinterval]
 
+    # check whether the addr/cidr overlaps the self.pool 
+    # for example, addr/cidr=172.16.0.48/29 overlaps self.pool['24']=[172.16.0.0]
+    def overlap(self, addr, cidr):
+        cidr=int(cidr)
+        start_cidr=int(self.info.split('/')[1])
+        # test self.pool[cidr] from first cidr pool to last cidr pool
+        for cur_cidr in range(start_cidr, 33):
+            if not self.pool[str(cur_cidr)]:
+                continue
+            # for every cur_cidr, test every possible element covered by pool[cur_cidr] in range of addr/cidr
+            cur_addr=fix_ip(addr, min(cidr, cur_cidr))
+            last_addr=next_interval(addr, cidr)
+            while(ip_to_int(cur_addr)<ip_to_int(last_addr)):
+                if cur_addr in self.pool[str(cur_cidr)]:
+                    return  True
+                cur_addr=next_interval(cur_addr, cur_cidr)
+        return False
+
+    # whether addr/cidr is in the range of self.pool
+    def inrange(self, addr, cidr):
+         pool_addr,pool_cidr=self.info.split('/')
+         if int(cidr)>=int(pool_cidr) and fix_ip(addr,pool_cidr)==pool_addr:
+             return True
+         else:
+             return False
+
     # deallocate an interval with IP/CIDR
-    # ToDo : when free IP/CIDR, we donot check whether IP/CIDR is in pool
-    #        maybe we check this later
     def free(self, addr, cidr):
+        if not self.inrange(addr, cidr):
+            return [False, '%s/%s not in range of %s' % (addr, str(cidr), self.info)]
+        if self.overlap(addr, cidr):
+            return [False, '%s/%s overlaps the center pool:%s' % (addr, str(cidr), self.__str__())]
         cidr = int(cidr)
         # cidr not in pool means CIDR out of pool range
         if str(cidr) not in self.pool:
@@ -185,14 +213,24 @@ class EnumPool(object):
             return [status, result]
         return [True, list(map(lambda x:x+"/"+self.info.split('/')[1], result))]
 
-    # ToDo : when release :
-    #               not check whether IP is in the range of pool
-    #               not check whether IP is already in the pool
+    def inrange(self, ip):
+        addr = self.info.split('/')[0]
+        addrint = ip_to_int(addr)
+        cidr = int(self.info.split('/')[1])
+        if addrint+1 <= ip_to_int(ip) <= addrint+pow(2, 32-cidr)-2:
+            return True
+        return False
+
     def release(self, ip_or_ips):
         if type(ip_or_ips) == str:
             ips = [ ip_or_ips ]
         else:
             ips = ip_or_ips
+        # check whether all IPs are not in the pool but in the range of pool 
+        for ip in ips:
+            ip = ip.split('/')[0]
+            if (ip in self.pool) or (not self.inrange(ip)):
+                return [False, 'release IPs failed for ip already existing or ip exceeding the network pool, ips to be released: %s, ip pool is: %s and content is : %s' % (ips, self.info, self.pool)]
         for ip in ips:
             # maybe ip is in format IP/CIDR
             ip = ip.split('/')[0]
@@ -221,6 +259,14 @@ class UserPool(EnumPool):
     def get_gateway_cidr(self):
         return self.gateway+"/"+self.info.split('/')[1]
 
+    def inrange(self, ip):
+        addr = self.info.split('/')[0]
+        addrint = ip_to_int(addr)
+        cidr = int(self.info.split('/')[1])
+        if addrint+2 <= ip_to_int(ip) <= addrint+pow(2, 32-cidr)-2:
+            return True
+        return False
+
     def printpool(self):
         print("users ID:"+str(self.vlanid)+",  net info:"+self.info+",  gateway:"+self.gateway)
         print (str(self.pool))