arp.java

Java Op Processor java vhdl processor

package tcpip;

/**
*	Arp.java: does ARP.
*
*	Author: Martin Schoeberl ([e-mail])
*
*   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.*;

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$<protocol>.
	 8.bit: (ar$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
		}
	}

}