7 * \defgroup uiparp uIP Address Resolution Protocol
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10 * The Address Resolution Protocol ARP is used for mapping between IP
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11 * addresses and link level addresses such as the Ethernet MAC
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12 * addresses. ARP uses broadcast queries to ask for the link level
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13 * address of a known IP address and the host which is configured with
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14 * the IP address for which the query was meant, will respond with its
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15 * link level address.
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17 * \note This ARP implementation only supports Ethernet.
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22 * Implementation of the ARP Address Resolution Protocol.
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23 * \author Adam Dunkels <adam@dunkels.com>
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28 * Copyright (c) 2001-2003, Adam Dunkels.
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29 * All rights reserved.
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31 * Redistribution and use in source and binary forms, with or without
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32 * modification, are permitted provided that the following conditions
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34 * 1. Redistributions of source code must retain the above copyright
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35 * notice, this list of conditions and the following disclaimer.
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36 * 2. Redistributions in binary form must reproduce the above copyright
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37 * notice, this list of conditions and the following disclaimer in the
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38 * documentation and/or other materials provided with the distribution.
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39 * 3. The name of the author may not be used to endorse or promote
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40 * products derived from this software without specific prior
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41 * written permission.
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43 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS
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44 * OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
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45 * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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46 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
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47 * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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48 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE
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49 * GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
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50 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
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51 * WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
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52 * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
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53 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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55 * This file is part of the uIP TCP/IP stack.
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57 * $Id: uip_arp.c,v 1.8 2006/06/02 23:36:21 adam Exp $
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62 #include "uip_arp.h"
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71 struct uip_eth_hdr ethhdr;
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77 struct uip_eth_addr shwaddr;
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79 struct uip_eth_addr dhwaddr;
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92 struct uip_eth_hdr ethhdr;
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102 u16_t srcipaddr[2],
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110 #define ARP_REQUEST 1
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111 #define ARP_REPLY 2
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113 #define ARP_HWTYPE_ETH 1
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117 struct uip_eth_addr ethaddr;
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121 static const struct uip_eth_addr broadcast_ethaddr =
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122 {{0xff,0xff,0xff,0xff,0xff,0xff}};
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123 static const u16_t broadcast_ipaddr[2] = {0xffff,0xffff};
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125 static struct arp_entry arp_table[UIP_ARPTAB_SIZE];
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126 static u16_t ipaddr[2];
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129 static u8_t arptime;
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130 static u8_t tmpage;
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132 #define BUF ((struct arp_hdr *)&uip_buf[0])
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133 #define IPBUF ((struct ethip_hdr *)&uip_buf[0])
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134 /*-----------------------------------------------------------------------------------*/
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136 * Initialize the ARP module.
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139 /*-----------------------------------------------------------------------------------*/
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143 for(i = 0; i < UIP_ARPTAB_SIZE; ++i) {
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144 memset(arp_table[i].ipaddr, 0, 4);
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147 /*-----------------------------------------------------------------------------------*/
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149 * Periodic ARP processing function.
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151 * This function performs periodic timer processing in the ARP module
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152 * and should be called at regular intervals. The recommended interval
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153 * is 10 seconds between the calls.
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156 /*-----------------------------------------------------------------------------------*/
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158 uip_arp_timer(void)
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160 struct arp_entry *tabptr;
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163 for(i = 0; i < UIP_ARPTAB_SIZE; ++i) {
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164 tabptr = &arp_table[i];
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165 if((tabptr->ipaddr[0] | tabptr->ipaddr[1]) != 0 &&
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166 arptime - tabptr->time >= UIP_ARP_MAXAGE) {
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167 memset(tabptr->ipaddr, 0, 4);
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172 /*-----------------------------------------------------------------------------------*/
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174 uip_arp_update(u16_t *ipaddr, struct uip_eth_addr *ethaddr)
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176 register struct arp_entry *tabptr;
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177 /* Walk through the ARP mapping table and try to find an entry to
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178 update. If none is found, the IP -> MAC address mapping is
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179 inserted in the ARP table. */
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180 for(i = 0; i < UIP_ARPTAB_SIZE; ++i) {
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182 tabptr = &arp_table[i];
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183 /* Only check those entries that are actually in use. */
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184 if(tabptr->ipaddr[0] != 0 &&
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185 tabptr->ipaddr[1] != 0) {
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187 /* Check if the source IP address of the incoming packet matches
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188 the IP address in this ARP table entry. */
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189 if(ipaddr[0] == tabptr->ipaddr[0] &&
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190 ipaddr[1] == tabptr->ipaddr[1]) {
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192 /* An old entry found, update this and return. */
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193 memcpy(tabptr->ethaddr.addr, ethaddr->addr, 6);
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194 tabptr->time = arptime;
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201 /* If we get here, no existing ARP table entry was found, so we
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204 /* First, we try to find an unused entry in the ARP table. */
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205 for(i = 0; i < UIP_ARPTAB_SIZE; ++i) {
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206 tabptr = &arp_table[i];
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207 if(tabptr->ipaddr[0] == 0 &&
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208 tabptr->ipaddr[1] == 0) {
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213 /* If no unused entry is found, we try to find the oldest entry and
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215 if(i == UIP_ARPTAB_SIZE) {
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218 for(i = 0; i < UIP_ARPTAB_SIZE; ++i) {
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219 tabptr = &arp_table[i];
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220 if(arptime - tabptr->time > tmpage) {
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221 tmpage = arptime - tabptr->time;
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226 tabptr = &arp_table[i];
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229 /* Now, i is the ARP table entry which we will fill with the new
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231 memcpy(tabptr->ipaddr, ipaddr, 4);
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232 memcpy(tabptr->ethaddr.addr, ethaddr->addr, 6);
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233 tabptr->time = arptime;
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235 /*-----------------------------------------------------------------------------------*/
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237 * ARP processing for incoming IP packets
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239 * This function should be called by the device driver when an IP
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240 * packet has been received. The function will check if the address is
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241 * in the ARP cache, and if so the ARP cache entry will be
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242 * refreshed. If no ARP cache entry was found, a new one is created.
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244 * This function expects an IP packet with a prepended Ethernet header
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245 * in the uip_buf[] buffer, and the length of the packet in the global
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246 * variable uip_len.
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248 /*-----------------------------------------------------------------------------------*/
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253 uip_len -= sizeof(struct uip_eth_hdr);
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255 /* Only insert/update an entry if the source IP address of the
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256 incoming IP packet comes from a host on the local network. */
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257 if((IPBUF->srcipaddr[0] & uip_netmask[0]) !=
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258 (uip_hostaddr[0] & uip_netmask[0])) {
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261 if((IPBUF->srcipaddr[1] & uip_netmask[1]) !=
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262 (uip_hostaddr[1] & uip_netmask[1])) {
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265 uip_arp_update(IPBUF->srcipaddr, &(IPBUF->ethhdr.src));
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270 /*-----------------------------------------------------------------------------------*/
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272 * ARP processing for incoming ARP packets.
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274 * This function should be called by the device driver when an ARP
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275 * packet has been received. The function will act differently
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276 * depending on the ARP packet type: if it is a reply for a request
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277 * that we previously sent out, the ARP cache will be filled in with
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278 * the values from the ARP reply. If the incoming ARP packet is an ARP
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279 * request for our IP address, an ARP reply packet is created and put
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280 * into the uip_buf[] buffer.
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282 * When the function returns, the value of the global variable uip_len
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283 * indicates whether the device driver should send out a packet or
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284 * not. If uip_len is zero, no packet should be sent. If uip_len is
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285 * non-zero, it contains the length of the outbound packet that is
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286 * present in the uip_buf[] buffer.
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288 * This function expects an ARP packet with a prepended Ethernet
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289 * header in the uip_buf[] buffer, and the length of the packet in the
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290 * global variable uip_len.
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292 /*-----------------------------------------------------------------------------------*/
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294 uip_arp_arpin(void)
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297 if(uip_len < sizeof(struct arp_hdr)) {
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303 switch(BUF->opcode) {
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304 case HTONS(ARP_REQUEST):
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305 /* ARP request. If it asked for our address, we send out a
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307 if(uip_ipaddr_cmp(BUF->dipaddr, uip_hostaddr)) {
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308 /* First, we register the one who made the request in our ARP
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309 table, since it is likely that we will do more communication
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310 with this host in the future. */
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311 uip_arp_update(BUF->sipaddr, &BUF->shwaddr);
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313 /* The reply opcode is 2. */
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314 BUF->opcode = HTONS(2);
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316 memcpy(BUF->dhwaddr.addr, BUF->shwaddr.addr, 6);
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317 memcpy(BUF->shwaddr.addr, uip_ethaddr.addr, 6);
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318 memcpy(BUF->ethhdr.src.addr, uip_ethaddr.addr, 6);
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319 memcpy(BUF->ethhdr.dest.addr, BUF->dhwaddr.addr, 6);
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321 BUF->dipaddr[0] = BUF->sipaddr[0];
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322 BUF->dipaddr[1] = BUF->sipaddr[1];
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323 BUF->sipaddr[0] = uip_hostaddr[0];
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324 BUF->sipaddr[1] = uip_hostaddr[1];
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326 BUF->ethhdr.type = HTONS(UIP_ETHTYPE_ARP);
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327 uip_len = sizeof(struct arp_hdr);
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330 case HTONS(ARP_REPLY):
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331 /* ARP reply. We insert or update the ARP table if it was meant
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333 if(uip_ipaddr_cmp(BUF->dipaddr, uip_hostaddr)) {
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334 uip_arp_update(BUF->sipaddr, &BUF->shwaddr);
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341 /*-----------------------------------------------------------------------------------*/
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343 * Prepend Ethernet header to an outbound IP packet and see if we need
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344 * to send out an ARP request.
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346 * This function should be called before sending out an IP packet. The
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347 * function checks the destination IP address of the IP packet to see
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348 * what Ethernet MAC address that should be used as a destination MAC
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349 * address on the Ethernet.
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351 * If the destination IP address is in the local network (determined
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352 * by logical ANDing of netmask and our IP address), the function
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353 * checks the ARP cache to see if an entry for the destination IP
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354 * address is found. If so, an Ethernet header is prepended and the
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355 * function returns. If no ARP cache entry is found for the
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356 * destination IP address, the packet in the uip_buf[] is replaced by
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357 * an ARP request packet for the IP address. The IP packet is dropped
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358 * and it is assumed that they higher level protocols (e.g., TCP)
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359 * eventually will retransmit the dropped packet.
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361 * If the destination IP address is not on the local network, the IP
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362 * address of the default router is used instead.
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364 * When the function returns, a packet is present in the uip_buf[]
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365 * buffer, and the length of the packet is in the global variable
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368 /*-----------------------------------------------------------------------------------*/
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372 struct arp_entry *tabptr;
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374 /* Find the destination IP address in the ARP table and construct
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375 the Ethernet header. If the destination IP addres isn't on the
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376 local network, we use the default router's IP address instead.
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378 If not ARP table entry is found, we overwrite the original IP
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379 packet with an ARP request for the IP address. */
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381 /* First check if destination is a local broadcast. */
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382 if(uip_ipaddr_cmp(IPBUF->destipaddr, broadcast_ipaddr)) {
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383 memcpy(IPBUF->ethhdr.dest.addr, broadcast_ethaddr.addr, 6);
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385 /* Check if the destination address is on the local network. */
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386 if(!uip_ipaddr_maskcmp(IPBUF->destipaddr, uip_hostaddr, uip_netmask)) {
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387 /* Destination address was not on the local network, so we need to
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388 use the default router's IP address instead of the destination
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389 address when determining the MAC address. */
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390 uip_ipaddr_copy(ipaddr, uip_draddr);
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392 /* Else, we use the destination IP address. */
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393 uip_ipaddr_copy(ipaddr, IPBUF->destipaddr);
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396 for(i = 0; i < UIP_ARPTAB_SIZE; ++i) {
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397 tabptr = &arp_table[i];
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398 if(uip_ipaddr_cmp(ipaddr, tabptr->ipaddr)) {
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403 if(i == UIP_ARPTAB_SIZE) {
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404 /* The destination address was not in our ARP table, so we
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405 overwrite the IP packet with an ARP request. */
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407 memset(BUF->ethhdr.dest.addr, 0xff, 6);
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408 memset(BUF->dhwaddr.addr, 0x00, 6);
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409 memcpy(BUF->ethhdr.src.addr, uip_ethaddr.addr, 6);
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410 memcpy(BUF->shwaddr.addr, uip_ethaddr.addr, 6);
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412 uip_ipaddr_copy(BUF->dipaddr, ipaddr);
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413 uip_ipaddr_copy(BUF->sipaddr, uip_hostaddr);
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414 BUF->opcode = HTONS(ARP_REQUEST); /* ARP request. */
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415 BUF->hwtype = HTONS(ARP_HWTYPE_ETH);
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416 BUF->protocol = HTONS(UIP_ETHTYPE_IP);
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419 BUF->ethhdr.type = HTONS(UIP_ETHTYPE_ARP);
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421 uip_appdata = &uip_buf[UIP_TCPIP_HLEN + UIP_LLH_LEN];
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423 uip_len = sizeof(struct arp_hdr);
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427 /* Build an ethernet header. */
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428 memcpy(IPBUF->ethhdr.dest.addr, tabptr->ethaddr.addr, 6);
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430 memcpy(IPBUF->ethhdr.src.addr, uip_ethaddr.addr, 6);
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432 IPBUF->ethhdr.type = HTONS(UIP_ETHTYPE_IP);
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434 uip_len += sizeof(struct uip_eth_hdr);
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436 /*-----------------------------------------------------------------------------------*/
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