For some purposes, disabling ARP may be desired, in order to study network properties in the ns-2 simulator. In ns-2, the MAC and IP addresses are the same, making ARP disabling very easy. To disable the ARP protocol in ns-2.34, add these lines to the top of ARPTable::arpresolve in the file mac/arp.cc:
hdr_cmn *ch = HDR_CMN(p);
mac_->hdr_dst((char*) HDR_MAC(p), ch->next_hop());
Referred from a mail exchange between Ahmad Khayyat and Pedro Vale Estrela.