www.pudn.com > ejip.zip > Arp.java

/* 
 * Copyright (c) Martin Schoeberl, martin@jopdesign.com 
 * All rights reserved. 
 * 
 * Redistribution and use in source and binary forms, with or without 
 * modification, are permitted provided that the following conditions 
 * are met: 
 * 1. Redistributions of source code must retain the above copyright 
 *    notice, this list of conditions and the following disclaimer. 
 * 2. Redistributions in binary form must reproduce the above copyright 
 *    notice, this list of conditions and the following disclaimer in the 
 *    documentation and/or other materials provided with the distribution. 
 * 3. All advertising materials mentioning features or use of this software 
 *    must display the following acknowledgement: 
 *	This product includes software developed by Martin Schoeberl 
 * 
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 
 * SUCH DAMAGE. 
 * 
 */ 
 
package ejip; 
 
/** 
*	Arp.java: does ARP. 
* 
*	Author: Martin Schoeberl (martin.schoeberl@chello.at) 
* 
*   Changelog: 
*		2002-03-15	ARP works! 
*		2002-10-21	use Packet buffer, 4 bytes in one word 
*		2002-11-11	ARP in own class (called from LinkLayer driver). 
* 
* 
*/ 
 
import util.*; 
 
/** 
*	handle ARP request. 
*/ 
 
public class Arp { 
 
/** 
*	handle ARP request. 
*/ 
	protected static void request(Packet p, int[] eth, int ip) { 
 
		Dbg.wr('A'); 
 
		if (p.buf[6]==ip) { 
 
 
/* 
    Ethernet packet data: 
	16.bit: (ar$hrd) Hardware address space (e.g., Ethernet, 
			 Packet Radio Net.) 
	16.bit: (ar$pro) Protocol address space.  For Ethernet 
			 hardware, this is from the set of type 
			 fields ether_typ$. 
	 8.bit: (ar$hln) byte length of each hardware address 
	 8.bit: (ar$pln) byte length of each protocol address 
	16.bit: (ar$op)  opcode (ares_op$REQUEST | ares_op$REPLY) 
	nbytes: (ar$sha) Hardware address of sender of this 
			 packet, n from the ar$hln field. 
	mbytes: (ar$spa) Protocol address of sender of this 
			 packet, m from the ar$pln field. 
	nbytes: (ar$tha) Hardware address of target of this 
			 packet (if known). 
	mbytes: (ar$tpa) Protocol address of target. 
*/ 
			/* 
			Set the ar$op field to ares_op$REPLY 
			*/ 
			p.buf[1] = 0x06040002;	// hw-len, sw-len, opcode replay 
 
			/* 
			Swap hardware and protocol fields, putting the local 
	    	hardware and protocol addresses in the sender fields. 
			*/ 
			int ip_src = (p.buf[3]<<16) + (p.buf[4]>>>16); 
			p.buf[2] = (eth[0]<<24) + (eth[1]<<16) + (eth[2]<<8) + eth[3]; 
			p.buf[3] = (eth[4]<<24) + (eth[5]<<16) + (ip>>>16); 
			p.buf[4] = (ip<<16) + p.llh[3]; 
			p.buf[5] = (p.llh[4]<<16) + p.llh[5]; 
			p.buf[6] = ip_src; 
 
			/* 
			Send the packet to the (new) target hardware address on 
	    	the same hardware on which the request was received. 
			*/ 
 
			p.len = 46; 
			p.llh[0] = p.llh[3]; 
			p.llh[1] = p.llh[4]; 
			p.llh[2] = p.llh[5]; 
			p.llh[6] = 0x0806;			// ARP frame 
			p.setStatus(Packet.SND);	// mark packet ready to send 
		} else { 
			p.setStatus(Packet.FREE);			// mark packet free 
		} 
	} 
 
}