7 * \defgroup uiparp uIP Address Resolution Protocol
10 * The Address Resolution Protocol ARP is used for mapping between IP
11 * addresses and link level addresses such as the Ethernet MAC
12 * addresses. ARP uses broadcast queries to ask for the link level
13 * address of a known IP address and the host which is configured with
14 * the IP address for which the query was meant, will respond with its
17 * \note This ARP implementation only supports Ethernet.
22 * Implementation of the ARP Address Resolution Protocol.
23 * \author Adam Dunkels <adam@dunkels.com>
28 * Copyright (c) 2001-2003, Adam Dunkels.
29 * All rights reserved.
31 * Redistribution and use in source and binary forms, with or without
32 * modification, are permitted provided that the following conditions
34 * 1. Redistributions of source code must retain the above copyright
35 * notice, this list of conditions and the following disclaimer.
36 * 2. Redistributions in binary form must reproduce the above copyright
37 * notice, this list of conditions and the following disclaimer in the
38 * documentation and/or other materials provided with the distribution.
39 * 3. The name of the author may not be used to endorse or promote
40 * products derived from this software without specific prior
43 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS
44 * OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
45 * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
46 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
47 * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
48 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE
49 * GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
50 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
51 * WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
52 * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
53 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
55 * This file is part of the uIP TCP/IP stack.
57 * $Id: uip_arp.c,v 1.8 2006/06/02 23:36:21 adam Exp $
71 struct uip_eth_hdr ethhdr
;
77 struct uip_eth_addr shwaddr
;
79 struct uip_eth_addr dhwaddr
;
92 struct uip_eth_hdr ethhdr
;
110 #define ARP_REQUEST 1
113 #define ARP_HWTYPE_ETH 1
117 struct uip_eth_addr ethaddr
;
121 static const struct uip_eth_addr broadcast_ethaddr
=
122 {{0xff,0xff,0xff,0xff,0xff,0xff}};
123 static const u16_t broadcast_ipaddr
[2] = {0xffff,0xffff};
125 static struct arp_entry arp_table
[UIP_ARPTAB_SIZE
];
126 static u16_t ipaddr
[2];
132 #define BUF ((struct arp_hdr *)&uip_buf[0])
133 #define IPBUF ((struct ethip_hdr *)&uip_buf[0])
134 /*-----------------------------------------------------------------------------------*/
136 * Initialize the ARP module.
139 /*-----------------------------------------------------------------------------------*/
143 for(i
= 0; i
< UIP_ARPTAB_SIZE
; ++i
) {
144 memset(arp_table
[i
].ipaddr
, 0, 4);
147 /*-----------------------------------------------------------------------------------*/
149 * Periodic ARP processing function.
151 * This function performs periodic timer processing in the ARP module
152 * and should be called at regular intervals. The recommended interval
153 * is 10 seconds between the calls.
156 /*-----------------------------------------------------------------------------------*/
160 struct arp_entry
*tabptr
;
163 for(i
= 0; i
< UIP_ARPTAB_SIZE
; ++i
) {
164 tabptr
= &arp_table
[i
];
165 if((tabptr
->ipaddr
[0] | tabptr
->ipaddr
[1]) != 0 &&
166 arptime
- tabptr
->time
>= UIP_ARP_MAXAGE
) {
167 memset(tabptr
->ipaddr
, 0, 4);
172 /*-----------------------------------------------------------------------------------*/
174 uip_arp_update(u16_t
*ipaddr
, struct uip_eth_addr
*ethaddr
)
176 register struct arp_entry
*tabptr
;
177 /* Walk through the ARP mapping table and try to find an entry to
178 update. If none is found, the IP -> MAC address mapping is
179 inserted in the ARP table. */
180 for(i
= 0; i
< UIP_ARPTAB_SIZE
; ++i
) {
182 tabptr
= &arp_table
[i
];
183 /* Only check those entries that are actually in use. */
184 if(tabptr
->ipaddr
[0] != 0 &&
185 tabptr
->ipaddr
[1] != 0) {
187 /* Check if the source IP address of the incoming packet matches
188 the IP address in this ARP table entry. */
189 if(ipaddr
[0] == tabptr
->ipaddr
[0] &&
190 ipaddr
[1] == tabptr
->ipaddr
[1]) {
192 /* An old entry found, update this and return. */
193 memcpy(tabptr
->ethaddr
.addr
, ethaddr
->addr
, 6);
194 tabptr
->time
= arptime
;
201 /* If we get here, no existing ARP table entry was found, so we
204 /* First, we try to find an unused entry in the ARP table. */
205 for(i
= 0; i
< UIP_ARPTAB_SIZE
; ++i
) {
206 tabptr
= &arp_table
[i
];
207 if(tabptr
->ipaddr
[0] == 0 &&
208 tabptr
->ipaddr
[1] == 0) {
213 /* If no unused entry is found, we try to find the oldest entry and
215 if(i
== UIP_ARPTAB_SIZE
) {
218 for(i
= 0; i
< UIP_ARPTAB_SIZE
; ++i
) {
219 tabptr
= &arp_table
[i
];
220 if(arptime
- tabptr
->time
> tmpage
) {
221 tmpage
= arptime
- tabptr
->time
;
226 tabptr
= &arp_table
[i
];
229 /* Now, i is the ARP table entry which we will fill with the new
231 memcpy(tabptr
->ipaddr
, ipaddr
, 4);
232 memcpy(tabptr
->ethaddr
.addr
, ethaddr
->addr
, 6);
233 tabptr
->time
= arptime
;
235 /*-----------------------------------------------------------------------------------*/
237 * ARP processing for incoming IP packets
239 * This function should be called by the device driver when an IP
240 * packet has been received. The function will check if the address is
241 * in the ARP cache, and if so the ARP cache entry will be
242 * refreshed. If no ARP cache entry was found, a new one is created.
244 * This function expects an IP packet with a prepended Ethernet header
245 * in the uip_buf[] buffer, and the length of the packet in the global
248 /*-----------------------------------------------------------------------------------*/
253 uip_len
-= sizeof(struct uip_eth_hdr
);
255 /* Only insert/update an entry if the source IP address of the
256 incoming IP packet comes from a host on the local network. */
257 if((IPBUF
->srcipaddr
[0] & uip_netmask
[0]) !=
258 (uip_hostaddr
[0] & uip_netmask
[0])) {
261 if((IPBUF
->srcipaddr
[1] & uip_netmask
[1]) !=
262 (uip_hostaddr
[1] & uip_netmask
[1])) {
265 uip_arp_update(IPBUF
->srcipaddr
, &(IPBUF
->ethhdr
.src
));
270 /*-----------------------------------------------------------------------------------*/
272 * ARP processing for incoming ARP packets.
274 * This function should be called by the device driver when an ARP
275 * packet has been received. The function will act differently
276 * depending on the ARP packet type: if it is a reply for a request
277 * that we previously sent out, the ARP cache will be filled in with
278 * the values from the ARP reply. If the incoming ARP packet is an ARP
279 * request for our IP address, an ARP reply packet is created and put
280 * into the uip_buf[] buffer.
282 * When the function returns, the value of the global variable uip_len
283 * indicates whether the device driver should send out a packet or
284 * not. If uip_len is zero, no packet should be sent. If uip_len is
285 * non-zero, it contains the length of the outbound packet that is
286 * present in the uip_buf[] buffer.
288 * This function expects an ARP packet with a prepended Ethernet
289 * header in the uip_buf[] buffer, and the length of the packet in the
290 * global variable uip_len.
292 /*-----------------------------------------------------------------------------------*/
297 if(uip_len
< sizeof(struct arp_hdr
)) {
303 switch(BUF
->opcode
) {
304 case HTONS(ARP_REQUEST
):
305 /* ARP request. If it asked for our address, we send out a
307 if(uip_ipaddr_cmp(BUF
->dipaddr
, uip_hostaddr
)) {
308 /* First, we register the one who made the request in our ARP
309 table, since it is likely that we will do more communication
310 with this host in the future. */
311 uip_arp_update(BUF
->sipaddr
, &BUF
->shwaddr
);
313 /* The reply opcode is 2. */
314 BUF
->opcode
= HTONS(2);
316 memcpy(BUF
->dhwaddr
.addr
, BUF
->shwaddr
.addr
, 6);
317 memcpy(BUF
->shwaddr
.addr
, uip_ethaddr
.addr
, 6);
318 memcpy(BUF
->ethhdr
.src
.addr
, uip_ethaddr
.addr
, 6);
319 memcpy(BUF
->ethhdr
.dest
.addr
, BUF
->dhwaddr
.addr
, 6);
321 BUF
->dipaddr
[0] = BUF
->sipaddr
[0];
322 BUF
->dipaddr
[1] = BUF
->sipaddr
[1];
323 BUF
->sipaddr
[0] = uip_hostaddr
[0];
324 BUF
->sipaddr
[1] = uip_hostaddr
[1];
326 BUF
->ethhdr
.type
= HTONS(UIP_ETHTYPE_ARP
);
327 uip_len
= sizeof(struct arp_hdr
);
330 case HTONS(ARP_REPLY
):
331 /* ARP reply. We insert or update the ARP table if it was meant
333 if(uip_ipaddr_cmp(BUF
->dipaddr
, uip_hostaddr
)) {
334 uip_arp_update(BUF
->sipaddr
, &BUF
->shwaddr
);
341 /*-----------------------------------------------------------------------------------*/
343 * Prepend Ethernet header to an outbound IP packet and see if we need
344 * to send out an ARP request.
346 * This function should be called before sending out an IP packet. The
347 * function checks the destination IP address of the IP packet to see
348 * what Ethernet MAC address that should be used as a destination MAC
349 * address on the Ethernet.
351 * If the destination IP address is in the local network (determined
352 * by logical ANDing of netmask and our IP address), the function
353 * checks the ARP cache to see if an entry for the destination IP
354 * address is found. If so, an Ethernet header is prepended and the
355 * function returns. If no ARP cache entry is found for the
356 * destination IP address, the packet in the uip_buf[] is replaced by
357 * an ARP request packet for the IP address. The IP packet is dropped
358 * and it is assumed that they higher level protocols (e.g., TCP)
359 * eventually will retransmit the dropped packet.
361 * If the destination IP address is not on the local network, the IP
362 * address of the default router is used instead.
364 * When the function returns, a packet is present in the uip_buf[]
365 * buffer, and the length of the packet is in the global variable
368 /*-----------------------------------------------------------------------------------*/
372 struct arp_entry
*tabptr
;
374 /* Find the destination IP address in the ARP table and construct
375 the Ethernet header. If the destination IP addres isn't on the
376 local network, we use the default router's IP address instead.
378 If not ARP table entry is found, we overwrite the original IP
379 packet with an ARP request for the IP address. */
381 /* First check if destination is a local broadcast. */
382 if(uip_ipaddr_cmp(IPBUF
->destipaddr
, broadcast_ipaddr
)) {
383 memcpy(IPBUF
->ethhdr
.dest
.addr
, broadcast_ethaddr
.addr
, 6);
385 /* Check if the destination address is on the local network. */
386 if(!uip_ipaddr_maskcmp(IPBUF
->destipaddr
, uip_hostaddr
, uip_netmask
)) {
387 /* Destination address was not on the local network, so we need to
388 use the default router's IP address instead of the destination
389 address when determining the MAC address. */
390 uip_ipaddr_copy(ipaddr
, uip_draddr
);
392 /* Else, we use the destination IP address. */
393 uip_ipaddr_copy(ipaddr
, IPBUF
->destipaddr
);
396 for(i
= 0; i
< UIP_ARPTAB_SIZE
; ++i
) {
397 tabptr
= &arp_table
[i
];
398 if(uip_ipaddr_cmp(ipaddr
, tabptr
->ipaddr
)) {
403 if(i
== UIP_ARPTAB_SIZE
) {
404 /* The destination address was not in our ARP table, so we
405 overwrite the IP packet with an ARP request. */
407 memset(BUF
->ethhdr
.dest
.addr
, 0xff, 6);
408 memset(BUF
->dhwaddr
.addr
, 0x00, 6);
409 memcpy(BUF
->ethhdr
.src
.addr
, uip_ethaddr
.addr
, 6);
410 memcpy(BUF
->shwaddr
.addr
, uip_ethaddr
.addr
, 6);
412 uip_ipaddr_copy(BUF
->dipaddr
, ipaddr
);
413 uip_ipaddr_copy(BUF
->sipaddr
, uip_hostaddr
);
414 BUF
->opcode
= HTONS(ARP_REQUEST
); /* ARP request. */
415 BUF
->hwtype
= HTONS(ARP_HWTYPE_ETH
);
416 BUF
->protocol
= HTONS(UIP_ETHTYPE_IP
);
419 BUF
->ethhdr
.type
= HTONS(UIP_ETHTYPE_ARP
);
421 uip_appdata
= &uip_buf
[UIP_TCPIP_HLEN
+ UIP_LLH_LEN
];
423 uip_len
= sizeof(struct arp_hdr
);
427 /* Build an ethernet header. */
428 memcpy(IPBUF
->ethhdr
.dest
.addr
, tabptr
->ethaddr
.addr
, 6);
430 memcpy(IPBUF
->ethhdr
.src
.addr
, uip_ethaddr
.addr
, 6);
432 IPBUF
->ethhdr
.type
= HTONS(UIP_ETHTYPE_IP
);
434 uip_len
+= sizeof(struct uip_eth_hdr
);
436 /*-----------------------------------------------------------------------------------*/