To whom it may be concerned: Why does ip_rcv()/ip_queue_xmit() need "HOOK" before go to ip_rcv_finish ()/ip_queue_xmit2(); IP layer seems not to send ARP during makeing a outgoing IP packet; where does this code reside? I've searched arp.c, ip_output.c...etc, but still can't find arp-sending related codes.... I would also want to know if there's any useful Linux kernel 2.4.19 networking related documents? Or related books? Thanks for your help Best regards! Yi-Wen - : send the line "unsubscribe linux-net" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html