I like to understand why to check whether MAC is already present or not in the hash table. My understanding is once the MAC is authenticated and MAC is added to the Hash table, then the DHCP server start leasing the IP to the client, after successful leasing lease_added method i called. If my understanding is correct, what is the use of the adding MAC address check and not present condition. if the execution reaches lease_added method, that means MAC address is already inserted in the hash table. Can some one help here to understand the logic /**********tethering.c(lease_added)******************************/ DBG("ip address for lease added:%s",ip_addr); struct tether_client * teth_cli = NULL; if(true == g_hash_table_lookup_extended(clients_table, mac_addr, NULL, &teth_cli)) { DBG("modifying ip address for %s mac address from hash table",mac_addr); g_free(teth_cli->ip); teth_cli->ip = g_strdup(ip_addr); } else { DBG("no entry present for %s mac address",mac_addr); teth_cli = tether_client_create(ip_addr); if (teth_cli) { char * mac; mac = g_strdup(mac_addr); g_hash_table_insert(clients_table, mac, teth_cli); } } /*********************************************************************************/