1 /**
2 * \addtogroup uip
3 * @{
4 */
5
6 /**
7 * \defgroup uiparp uIP Address Resolution Protocol
8 * @{
9 *
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
15 * link level address.
16 *
17 * \note This ARP implementation only supports Ethernet.
18 */
19
20 /**
21 * \file
22 * Implementation of the ARP Address Resolution Protocol.
23 * \author Adam Dunkels <[email protected]>
24 *
25 */
26
27 /*
28 * Copyright (c) 2001-2003, Adam Dunkels.
29 * All rights reserved.
30 *
31 * Redistribution and use in source and binary forms, with or without
32 * modification, are permitted provided that the following conditions
33 * are met:
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
41 * written permission.
42 *
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.
54 *
55 * This file is part of the uIP TCP/IP stack.
56 *
57 * $Id: uip_arp.c,v 1.8 2006/06/02 23:36:21 adam Exp $
58 *
59 */
60
61
62 #include "uip_arp.h"
63
64 #include <string.h>
65
66 struct arp_hdr {
67 struct uip_eth_hdr ethhdr;
68 u16_t hwtype;
69 u16_t protocol;
70 u8_t hwlen;
71 u8_t protolen;
72 u16_t opcode;
73 struct uip_eth_addr shwaddr;
74 u16_t sipaddr[2];
75 struct uip_eth_addr dhwaddr;
76 u16_t dipaddr[2];
77 };
78
79 struct ethip_hdr {
80 struct uip_eth_hdr ethhdr;
81 /* IP header. */
82 u8_t vhl,
83 tos,
84 len[2],
85 ipid[2],
86 ipoffset[2],
87 ttl,
88 proto;
89 u16_t ipchksum;
90 u16_t srcipaddr[2],
91 destipaddr[2];
92 };
93
94 #define ARP_REQUEST 1
95 #define ARP_REPLY 2
96
97 #define ARP_HWTYPE_ETH 1
98
99 struct arp_entry {
100 u16_t ipaddr[2];
101 struct uip_eth_addr ethaddr;
102 u8_t time;
103 };
104
105 static const struct uip_eth_addr broadcast_ethaddr =
106 {{0xff,0xff,0xff,0xff,0xff,0xff}};
107 static const u16_t broadcast_ipaddr[2] = {0xffff,0xffff};
108
109 static struct arp_entry arp_table[UIP_ARPTAB_SIZE];
110 static u16_t ipaddr[2];
111 static u8_t i, c;
112
113 static u8_t arptime;
114 static u8_t tmpage;
115
116 #define BUF ((struct arp_hdr *)&uip_buf[0])
117 #define IPBUF ((struct ethip_hdr *)&uip_buf[0])
118 /*-----------------------------------------------------------------------------------*/
119 /**
120 * Initialize the ARP module.
121 *
122 */
123 /*-----------------------------------------------------------------------------------*/
124 void
uip_arp_init(void)125 uip_arp_init(void)
126 {
127 for(i = 0; i < UIP_ARPTAB_SIZE; ++i) {
128 memset(arp_table[i].ipaddr, 0, 4);
129 }
130 }
131 /*-----------------------------------------------------------------------------------*/
132 /**
133 * Periodic ARP processing function.
134 *
135 * This function performs periodic timer processing in the ARP module
136 * and should be called at regular intervals. The recommended interval
137 * is 10 seconds between the calls.
138 *
139 */
140 /*-----------------------------------------------------------------------------------*/
141 void
uip_arp_timer(void)142 uip_arp_timer(void)
143 {
144 struct arp_entry *tabptr;
145
146 ++arptime;
147 for(i = 0; i < UIP_ARPTAB_SIZE; ++i) {
148 tabptr = &arp_table[i];
149 if((tabptr->ipaddr[0] | tabptr->ipaddr[1]) != 0 &&
150 arptime - tabptr->time >= UIP_ARP_MAXAGE) {
151 memset(tabptr->ipaddr, 0, 4);
152 }
153 }
154
155 }
156 /*-----------------------------------------------------------------------------------*/
157 static void
uip_arp_update(u16_t * ipaddr,struct uip_eth_addr * ethaddr)158 uip_arp_update(u16_t *ipaddr, struct uip_eth_addr *ethaddr)
159 {
160 register struct arp_entry *tabptr;
161 /* Walk through the ARP mapping table and try to find an entry to
162 update. If none is found, the IP -> MAC address mapping is
163 inserted in the ARP table. */
164 for(i = 0; i < UIP_ARPTAB_SIZE; ++i) {
165
166 tabptr = &arp_table[i];
167 /* Only check those entries that are actually in use. */
168 if(tabptr->ipaddr[0] != 0 &&
169 tabptr->ipaddr[1] != 0) {
170
171 /* Check if the source IP address of the incoming packet matches
172 the IP address in this ARP table entry. */
173 if(ipaddr[0] == tabptr->ipaddr[0] &&
174 ipaddr[1] == tabptr->ipaddr[1]) {
175
176 /* An old entry found, update this and return. */
177 memcpy(tabptr->ethaddr.addr, ethaddr->addr, 6);
178 tabptr->time = arptime;
179
180 return;
181 }
182 }
183 }
184
185 /* If we get here, no existing ARP table entry was found, so we
186 create one. */
187
188 /* First, we try to find an unused entry in the ARP table. */
189 for(i = 0; i < UIP_ARPTAB_SIZE; ++i) {
190 tabptr = &arp_table[i];
191 if(tabptr->ipaddr[0] == 0 &&
192 tabptr->ipaddr[1] == 0) {
193 break;
194 }
195 }
196
197 /* If no unused entry is found, we try to find the oldest entry and
198 throw it away. */
199 if(i == UIP_ARPTAB_SIZE) {
200 tmpage = 0;
201 c = 0;
202 for(i = 0; i < UIP_ARPTAB_SIZE; ++i) {
203 tabptr = &arp_table[i];
204 if(arptime - tabptr->time > tmpage) {
205 tmpage = arptime - tabptr->time;
206 c = i;
207 }
208 }
209 i = c;
210 tabptr = &arp_table[i];
211 }
212
213 /* Now, i is the ARP table entry which we will fill with the new
214 information. */
215 memcpy(tabptr->ipaddr, ipaddr, 4);
216 memcpy(tabptr->ethaddr.addr, ethaddr->addr, 6);
217 tabptr->time = arptime;
218 }
219 /*-----------------------------------------------------------------------------------*/
220 /**
221 * ARP processing for incoming IP packets
222 *
223 * This function should be called by the device driver when an IP
224 * packet has been received. The function will check if the address is
225 * in the ARP cache, and if so the ARP cache entry will be
226 * refreshed. If no ARP cache entry was found, a new one is created.
227 *
228 * This function expects an IP packet with a prepended Ethernet header
229 * in the uip_buf[] buffer, and the length of the packet in the global
230 * variable uip_len.
231 */
232 /*-----------------------------------------------------------------------------------*/
233 #if 0
234 void
235 uip_arp_ipin(void)
236 {
237 uip_len -= sizeof(struct uip_eth_hdr);
238
239 /* Only insert/update an entry if the source IP address of the
240 incoming IP packet comes from a host on the local network. */
241 if((IPBUF->srcipaddr[0] & uip_netmask[0]) !=
242 (uip_hostaddr[0] & uip_netmask[0])) {
243 return;
244 }
245 if((IPBUF->srcipaddr[1] & uip_netmask[1]) !=
246 (uip_hostaddr[1] & uip_netmask[1])) {
247 return;
248 }
249 uip_arp_update(IPBUF->srcipaddr, &(IPBUF->ethhdr.src));
250
251 return;
252 }
253 #endif /* 0 */
254 /*-----------------------------------------------------------------------------------*/
255 /**
256 * ARP processing for incoming ARP packets.
257 *
258 * This function should be called by the device driver when an ARP
259 * packet has been received. The function will act differently
260 * depending on the ARP packet type: if it is a reply for a request
261 * that we previously sent out, the ARP cache will be filled in with
262 * the values from the ARP reply. If the incoming ARP packet is an ARP
263 * request for our IP address, an ARP reply packet is created and put
264 * into the uip_buf[] buffer.
265 *
266 * When the function returns, the value of the global variable uip_len
267 * indicates whether the device driver should send out a packet or
268 * not. If uip_len is zero, no packet should be sent. If uip_len is
269 * non-zero, it contains the length of the outbound packet that is
270 * present in the uip_buf[] buffer.
271 *
272 * This function expects an ARP packet with a prepended Ethernet
273 * header in the uip_buf[] buffer, and the length of the packet in the
274 * global variable uip_len.
275 */
276 /*-----------------------------------------------------------------------------------*/
277 void
uip_arp_arpin(void)278 uip_arp_arpin(void)
279 {
280
281 if(uip_len < sizeof(struct arp_hdr)) {
282 uip_len = 0;
283 return;
284 }
285 uip_len = 0;
286
287 switch(BUF->opcode) {
288 case HTONS(ARP_REQUEST):
289 /* ARP request. If it asked for our address, we send out a
290 reply. */
291 if(uip_ipaddr_cmp(BUF->dipaddr, uip_hostaddr)) {
292 /* First, we register the one who made the request in our ARP
293 table, since it is likely that we will do more communication
294 with this host in the future. */
295 uip_arp_update(BUF->sipaddr, &BUF->shwaddr);
296
297 /* The reply opcode is 2. */
298 BUF->opcode = HTONS(2);
299
300 memcpy(BUF->dhwaddr.addr, BUF->shwaddr.addr, 6);
301 memcpy(BUF->shwaddr.addr, uip_ethaddr.addr, 6);
302 memcpy(BUF->ethhdr.src.addr, uip_ethaddr.addr, 6);
303 memcpy(BUF->ethhdr.dest.addr, BUF->dhwaddr.addr, 6);
304
305 BUF->dipaddr[0] = BUF->sipaddr[0];
306 BUF->dipaddr[1] = BUF->sipaddr[1];
307 BUF->sipaddr[0] = uip_hostaddr[0];
308 BUF->sipaddr[1] = uip_hostaddr[1];
309
310 BUF->ethhdr.type = HTONS(UIP_ETHTYPE_ARP);
311 uip_len = sizeof(struct arp_hdr);
312 }
313 break;
314 case HTONS(ARP_REPLY):
315 /* ARP reply. We insert or update the ARP table if it was meant
316 for us. */
317 if(uip_ipaddr_cmp(BUF->dipaddr, uip_hostaddr)) {
318 uip_arp_update(BUF->sipaddr, &BUF->shwaddr);
319 }
320 break;
321 }
322
323 return;
324 }
325 /*-----------------------------------------------------------------------------------*/
326 /**
327 * Prepend Ethernet header to an outbound IP packet and see if we need
328 * to send out an ARP request.
329 *
330 * This function should be called before sending out an IP packet. The
331 * function checks the destination IP address of the IP packet to see
332 * what Ethernet MAC address that should be used as a destination MAC
333 * address on the Ethernet.
334 *
335 * If the destination IP address is in the local network (determined
336 * by logical ANDing of netmask and our IP address), the function
337 * checks the ARP cache to see if an entry for the destination IP
338 * address is found. If so, an Ethernet header is prepended and the
339 * function returns. If no ARP cache entry is found for the
340 * destination IP address, the packet in the uip_buf[] is replaced by
341 * an ARP request packet for the IP address. The IP packet is dropped
342 * and it is assumed that they higher level protocols (e.g., TCP)
343 * eventually will retransmit the dropped packet.
344 *
345 * If the destination IP address is not on the local network, the IP
346 * address of the default router is used instead.
347 *
348 * When the function returns, a packet is present in the uip_buf[]
349 * buffer, and the length of the packet is in the global variable
350 * uip_len.
351 */
352 /*-----------------------------------------------------------------------------------*/
353 void
uip_arp_out(void)354 uip_arp_out(void)
355 {
356 struct arp_entry *tabptr;
357
358 /* Find the destination IP address in the ARP table and construct
359 the Ethernet header. If the destination IP addres isn't on the
360 local network, we use the default router's IP address instead.
361
362 If not ARP table entry is found, we overwrite the original IP
363 packet with an ARP request for the IP address. */
364
365 /* First check if destination is a local broadcast. */
366 if(uip_ipaddr_cmp(IPBUF->destipaddr, broadcast_ipaddr)) {
367 memcpy(IPBUF->ethhdr.dest.addr, broadcast_ethaddr.addr, 6);
368 } else {
369 /* Check if the destination address is on the local network. */
370 if(!uip_ipaddr_maskcmp(IPBUF->destipaddr, uip_hostaddr, uip_netmask)) {
371 /* Destination address was not on the local network, so we need to
372 use the default router's IP address instead of the destination
373 address when determining the MAC address. */
374 uip_ipaddr_copy(ipaddr, uip_draddr);
375 } else {
376 /* Else, we use the destination IP address. */
377 uip_ipaddr_copy(ipaddr, IPBUF->destipaddr);
378 }
379
380 for(i = 0; i < UIP_ARPTAB_SIZE; ++i) {
381 tabptr = &arp_table[i];
382 if(uip_ipaddr_cmp(ipaddr, tabptr->ipaddr)) {
383 break;
384 }
385 }
386
387 if(i == UIP_ARPTAB_SIZE) {
388 /* The destination address was not in our ARP table, so we
389 overwrite the IP packet with an ARP request. */
390
391 memset(BUF->ethhdr.dest.addr, 0xff, 6);
392 memset(BUF->dhwaddr.addr, 0x00, 6);
393 memcpy(BUF->ethhdr.src.addr, uip_ethaddr.addr, 6);
394 memcpy(BUF->shwaddr.addr, uip_ethaddr.addr, 6);
395
396 uip_ipaddr_copy(BUF->dipaddr, ipaddr);
397 uip_ipaddr_copy(BUF->sipaddr, uip_hostaddr);
398 BUF->opcode = HTONS(ARP_REQUEST); /* ARP request. */
399 BUF->hwtype = HTONS(ARP_HWTYPE_ETH);
400 BUF->protocol = HTONS(UIP_ETHTYPE_IP);
401 BUF->hwlen = 6;
402 BUF->protolen = 4;
403 BUF->ethhdr.type = HTONS(UIP_ETHTYPE_ARP);
404
405 uip_appdata = &uip_buf[UIP_TCPIP_HLEN + UIP_LLH_LEN];
406
407 uip_len = sizeof(struct arp_hdr);
408 return;
409 }
410
411 /* Build an ethernet header. */
412 memcpy(IPBUF->ethhdr.dest.addr, tabptr->ethaddr.addr, 6);
413 }
414 memcpy(IPBUF->ethhdr.src.addr, uip_ethaddr.addr, 6);
415
416 IPBUF->ethhdr.type = HTONS(UIP_ETHTYPE_IP);
417
418 uip_len += sizeof(struct uip_eth_hdr);
419 }
420 /*-----------------------------------------------------------------------------------*/
421
422 /** @} */
423 /** @} */
424