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uip_arp.c

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00001 /**
00002  * \addtogroup uip
00003  * @{
00004  */
00005 
00006 /**
00007  * \defgroup uiparp uIP Address Resolution Protocol
00008  * @{
00009  * 
00010  * The Address Resolution Protocol ARP is used for mapping between IP
00011  * addresses and link level addresses such as the Ethernet MAC
00012  * addresses. ARP uses broadcast queries to ask for the link level
00013  * address of a known IP address and the host which is configured with
00014  * the IP address for which the query was meant, will respond with its
00015  * link level address.
00016  *
00017  * \note This ARP implementation only supports Ethernet.
00018  */
00019  
00020 /**
00021  * \file
00022  * Implementation of the ARP Address Resolution Protocol.
00023  * \author Adam Dunkels <adam@dunkels.com>
00024  *
00025  */
00026 
00027 /*
00028  * Copyright (c) 2001-2003, Adam Dunkels.
00029  * All rights reserved. 
00030  *
00031  * Redistribution and use in source and binary forms, with or without 
00032  * modification, are permitted provided that the following conditions 
00033  * are met: 
00034  * 1. Redistributions of source code must retain the above copyright 
00035  *    notice, this list of conditions and the following disclaimer. 
00036  * 2. Redistributions in binary form must reproduce the above copyright 
00037  *    notice, this list of conditions and the following disclaimer in the 
00038  *    documentation and/or other materials provided with the distribution. 
00039  * 3. The name of the author may not be used to endorse or promote
00040  *    products derived from this software without specific prior
00041  *    written permission.  
00042  *
00043  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS
00044  * OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
00045  * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
00046  * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
00047  * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
00048  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE
00049  * GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
00050  * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
00051  * WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
00052  * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
00053  * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.  
00054  *
00055  * This file is part of the uIP TCP/IP stack.
00056  *
00057  * $Id: uip_arp.c,v 1.1 2006/06/17 22:41:19 adamdunkels Exp $
00058  *
00059  */
00060 
00061 
00062 #include "net/uip_arp.h"
00063 
00064 #include <string.h>
00065 
00066 struct arp_hdr {
00067   struct uip_eth_hdr ethhdr;
00068   u16_t hwtype;
00069   u16_t protocol;
00070   u8_t hwlen;
00071   u8_t protolen;
00072   u16_t opcode;
00073   struct uip_eth_addr shwaddr;
00074   u16_t sipaddr[2];
00075   struct uip_eth_addr dhwaddr;
00076   u16_t dipaddr[2]; 
00077 };
00078 
00079 struct ethip_hdr {
00080   struct uip_eth_hdr ethhdr;
00081   /* IP header. */
00082   u8_t vhl,
00083     tos,          
00084     len[2],       
00085     ipid[2],        
00086     ipoffset[2],  
00087     ttl,          
00088     proto;     
00089   u16_t ipchksum;
00090   u16_t srcipaddr[2], 
00091     destipaddr[2];
00092 };
00093 
00094 #define ARP_REQUEST 1
00095 #define ARP_REPLY   2
00096 
00097 #define ARP_HWTYPE_ETH 1
00098 
00099 struct arp_entry {
00100   u16_t ipaddr[2];
00101   struct uip_eth_addr ethaddr;
00102   u8_t time;
00103 };
00104 
00105 static const struct uip_eth_addr broadcast_ethaddr =
00106   {{0xff,0xff,0xff,0xff,0xff,0xff}};
00107 static const u16_t broadcast_ipaddr[2] = {0xffff,0xffff};
00108 
00109 static struct arp_entry arp_table[UIP_ARPTAB_SIZE];
00110 static u16_t ipaddr[2];
00111 static u8_t i, c;
00112 
00113 static u8_t arptime;
00114 static u8_t tmpage;
00115 
00116 #define BUF   ((struct arp_hdr *)&uip_buf[0])
00117 #define IPBUF ((struct ethip_hdr *)&uip_buf[0])
00118 /*-----------------------------------------------------------------------------------*/
00119 /**
00120  * Initialize the ARP module.
00121  *
00122  */
00123 /*-----------------------------------------------------------------------------------*/
00124 void
00125 uip_arp_init(void)
00126 {
00127   for(i = 0; i < UIP_ARPTAB_SIZE; ++i) {
00128     memset(arp_table[i].ipaddr, 0, 4);
00129   }
00130 }
00131 /*-----------------------------------------------------------------------------------*/
00132 /**
00133  * Periodic ARP processing function.
00134  *
00135  * This function performs periodic timer processing in the ARP module
00136  * and should be called at regular intervals. The recommended interval
00137  * is 10 seconds between the calls.
00138  *
00139  */
00140 /*-----------------------------------------------------------------------------------*/
00141 void
00142 uip_arp_timer(void)
00143 {
00144   struct arp_entry *tabptr;
00145   
00146   ++arptime;
00147   for(i = 0; i < UIP_ARPTAB_SIZE; ++i) {
00148     tabptr = &arp_table[i];
00149     if((tabptr->ipaddr[0] | tabptr->ipaddr[1]) != 0 &&
00150        arptime - tabptr->time >= UIP_ARP_MAXAGE) {
00151       memset(tabptr->ipaddr, 0, 4);
00152     }
00153   }
00154 
00155 }
00156 /*-----------------------------------------------------------------------------------*/
00157 static void
00158 uip_arp_update(u16_t *ipaddr, struct uip_eth_addr *ethaddr)
00159 {
00160   register struct arp_entry *tabptr;
00161   /* Walk through the ARP mapping table and try to find an entry to
00162      update. If none is found, the IP -> MAC address mapping is
00163      inserted in the ARP table. */
00164   for(i = 0; i < UIP_ARPTAB_SIZE; ++i) {
00165 
00166     tabptr = &arp_table[i];
00167     /* Only check those entries that are actually in use. */
00168     if(tabptr->ipaddr[0] != 0 &&
00169        tabptr->ipaddr[1] != 0) {
00170 
00171       /* Check if the source IP address of the incoming packet matches
00172          the IP address in this ARP table entry. */
00173       if(ipaddr[0] == tabptr->ipaddr[0] &&
00174          ipaddr[1] == tabptr->ipaddr[1]) {
00175          
00176         /* An old entry found, update this and return. */
00177         memcpy(tabptr->ethaddr.addr, ethaddr->addr, 6);
00178         tabptr->time = arptime;
00179 
00180         return;
00181       }
00182     }
00183   }
00184 
00185   /* If we get here, no existing ARP table entry was found, so we
00186      create one. */
00187 
00188   /* First, we try to find an unused entry in the ARP table. */
00189   for(i = 0; i < UIP_ARPTAB_SIZE; ++i) {
00190     tabptr = &arp_table[i];
00191     if(tabptr->ipaddr[0] == 0 &&
00192        tabptr->ipaddr[1] == 0) {
00193       break;
00194     }
00195   }
00196 
00197   /* If no unused entry is found, we try to find the oldest entry and
00198      throw it away. */
00199   if(i == UIP_ARPTAB_SIZE) {
00200     tmpage = 0;
00201     c = 0;
00202     for(i = 0; i < UIP_ARPTAB_SIZE; ++i) {
00203       tabptr = &arp_table[i];
00204       if(arptime - tabptr->time > tmpage) {
00205         tmpage = arptime - tabptr->time;
00206         c = i;
00207       }
00208     }
00209     i = c;
00210     tabptr = &arp_table[i];
00211   }
00212 
00213   /* Now, i is the ARP table entry which we will fill with the new
00214      information. */
00215   memcpy(tabptr->ipaddr, ipaddr, 4);
00216   memcpy(tabptr->ethaddr.addr, ethaddr->addr, 6);
00217   tabptr->time = arptime;
00218 }
00219 /*-----------------------------------------------------------------------------------*/
00220 /**
00221  * ARP processing for incoming IP packets
00222  *
00223  * This function should be called by the device driver when an IP
00224  * packet has been received. The function will check if the address is
00225  * in the ARP cache, and if so the ARP cache entry will be
00226  * refreshed. If no ARP cache entry was found, a new one is created.
00227  *
00228  * This function expects an IP packet with a prepended Ethernet header
00229  * in the uip_buf[] buffer, and the length of the packet in the global
00230  * variable uip_len.
00231  */
00232 /*-----------------------------------------------------------------------------------*/
00233 #if 0
00234 void
00235 uip_arp_ipin(void)
00236 {
00237   uip_len -= sizeof(struct uip_eth_hdr);
00238         
00239   /* Only insert/update an entry if the source IP address of the
00240      incoming IP packet comes from a host on the local network. */
00241   if((IPBUF->srcipaddr[0] & uip_netmask[0]) !=
00242      (uip_hostaddr[0] & uip_netmask[0])) {
00243     return;
00244   }
00245   if((IPBUF->srcipaddr[1] & uip_netmask[1]) !=
00246      (uip_hostaddr[1] & uip_netmask[1])) {
00247     return;
00248   }
00249   uip_arp_update(IPBUF->srcipaddr, &(IPBUF->ethhdr.src));
00250   
00251   return;
00252 }
00253 #endif /* 0 */
00254 /*-----------------------------------------------------------------------------------*/
00255 /**
00256  * ARP processing for incoming ARP packets.
00257  *
00258  * This function should be called by the device driver when an ARP
00259  * packet has been received. The function will act differently
00260  * depending on the ARP packet type: if it is a reply for a request
00261  * that we previously sent out, the ARP cache will be filled in with
00262  * the values from the ARP reply. If the incoming ARP packet is an ARP
00263  * request for our IP address, an ARP reply packet is created and put
00264  * into the uip_buf[] buffer.
00265  *
00266  * When the function returns, the value of the global variable uip_len
00267  * indicates whether the device driver should send out a packet or
00268  * not. If uip_len is zero, no packet should be sent. If uip_len is
00269  * non-zero, it contains the length of the outbound packet that is
00270  * present in the uip_buf[] buffer.
00271  *
00272  * This function expects an ARP packet with a prepended Ethernet
00273  * header in the uip_buf[] buffer, and the length of the packet in the
00274  * global variable uip_len.
00275  */
00276 /*-----------------------------------------------------------------------------------*/
00277 void
00278 uip_arp_arpin(void)
00279 {
00280   
00281   if(uip_len < sizeof(struct arp_hdr)) {
00282     uip_len = 0;
00283     return;
00284   }
00285   uip_len = 0;
00286   
00287   switch(BUF->opcode) {
00288   case HTONS(ARP_REQUEST):
00289     /* ARP request. If it asked for our address, we send out a
00290        reply. */    
00291     /*    if(BUF->dipaddr[0] == uip_hostaddr[0] &&
00292           BUF->dipaddr[1] == uip_hostaddr[1]) {*/
00293     if(uip_ipaddr_cmp(BUF->dipaddr, uip_hostaddr)) {
00294       /* First, we register the one who made the request in our ARP
00295          table, since it is likely that we will do more communication
00296          with this host in the future. */
00297       uip_arp_update(BUF->sipaddr, &BUF->shwaddr);
00298       
00299       /* The reply opcode is 2. */
00300       BUF->opcode = HTONS(2);
00301 
00302       memcpy(BUF->dhwaddr.addr, BUF->shwaddr.addr, 6);
00303       memcpy(BUF->shwaddr.addr, uip_ethaddr.addr, 6);
00304       memcpy(BUF->ethhdr.src.addr, uip_ethaddr.addr, 6);
00305       memcpy(BUF->ethhdr.dest.addr, BUF->dhwaddr.addr, 6);
00306       
00307       BUF->dipaddr[0] = BUF->sipaddr[0];
00308       BUF->dipaddr[1] = BUF->sipaddr[1];
00309       BUF->sipaddr[0] = uip_hostaddr[0];
00310       BUF->sipaddr[1] = uip_hostaddr[1];
00311 
00312       BUF->ethhdr.type = HTONS(UIP_ETHTYPE_ARP);      
00313       uip_len = sizeof(struct arp_hdr);
00314     }      
00315     break;
00316   case HTONS(ARP_REPLY):
00317     /* ARP reply. We insert or update the ARP table if it was meant
00318        for us. */
00319     /*    if(BUF->dipaddr[0] == uip_hostaddr[0] &&
00320           BUF->dipaddr[1] == uip_hostaddr[1]) {*/
00321     if(uip_ipaddr_cmp(BUF->dipaddr, uip_hostaddr)) {
00322       uip_arp_update(BUF->sipaddr, &BUF->shwaddr);
00323     }
00324     break;
00325   }
00326 
00327   return;
00328 }
00329 /*-----------------------------------------------------------------------------------*/
00330 /**
00331  * Prepend Ethernet header to an outbound IP packet and see if we need
00332  * to send out an ARP request.
00333  *
00334  * This function should be called before sending out an IP packet. The
00335  * function checks the destination IP address of the IP packet to see
00336  * what Ethernet MAC address that should be used as a destination MAC
00337  * address on the Ethernet.
00338  *
00339  * If the destination IP address is in the local network (determined
00340  * by logical ANDing of netmask and our IP address), the function
00341  * checks the ARP cache to see if an entry for the destination IP
00342  * address is found. If so, an Ethernet header is prepended and the
00343  * function returns. If no ARP cache entry is found for the
00344  * destination IP address, the packet in the uip_buf[] is replaced by
00345  * an ARP request packet for the IP address. The IP packet is dropped
00346  * and it is assumed that they higher level protocols (e.g., TCP)
00347  * eventually will retransmit the dropped packet.
00348  *
00349  * If the destination IP address is not on the local network, the IP
00350  * address of the default router is used instead.
00351  *
00352  * When the function returns, a packet is present in the uip_buf[]
00353  * buffer, and the length of the packet is in the global variable
00354  * uip_len.
00355  */
00356 /*-----------------------------------------------------------------------------------*/
00357 void
00358 uip_arp_out(void)
00359 {
00360   struct arp_entry *tabptr;
00361   
00362   /* Find the destination IP address in the ARP table and construct
00363      the Ethernet header. If the destination IP addres isn't on the
00364      local network, we use the default router's IP address instead.
00365 
00366      If not ARP table entry is found, we overwrite the original IP
00367      packet with an ARP request for the IP address. */
00368 
00369   /* First check if destination is a local broadcast. */
00370   if(uip_ipaddr_cmp(IPBUF->destipaddr, broadcast_ipaddr)) {
00371     memcpy(IPBUF->ethhdr.dest.addr, broadcast_ethaddr.addr, 6);
00372   } else {
00373     /* Check if the destination address is on the local network. */
00374     if(!uip_ipaddr_maskcmp(IPBUF->destipaddr, uip_hostaddr, uip_netmask)) {
00375       /* Destination address was not on the local network, so we need to
00376          use the default router's IP address instead of the destination
00377          address when determining the MAC address. */
00378       uip_ipaddr_copy(ipaddr, uip_draddr); 
00379     } else {
00380       /* Else, we use the destination IP address. */
00381       uip_ipaddr_copy(ipaddr, IPBUF->destipaddr); 
00382     }
00383       
00384     for(i = 0; i < UIP_ARPTAB_SIZE; ++i) {
00385       tabptr = &arp_table[i];
00386       if(uip_ipaddr_cmp(ipaddr, tabptr->ipaddr)) {
00387         break;
00388       }
00389     }
00390 
00391     if(i == UIP_ARPTAB_SIZE) {
00392       /* The destination address was not in our ARP table, so we
00393          overwrite the IP packet with an ARP request. */
00394 
00395       memset(BUF->ethhdr.dest.addr, 0xff, 6);
00396       memset(BUF->dhwaddr.addr, 0x00, 6);
00397       memcpy(BUF->ethhdr.src.addr, uip_ethaddr.addr, 6);
00398       memcpy(BUF->shwaddr.addr, uip_ethaddr.addr, 6);
00399     
00400       uip_ipaddr_copy(BUF->dipaddr, ipaddr);
00401       uip_ipaddr_copy(BUF->sipaddr, uip_hostaddr);
00402       BUF->opcode = HTONS(ARP_REQUEST); /* ARP request. */
00403       BUF->hwtype = HTONS(ARP_HWTYPE_ETH);
00404       BUF->protocol = HTONS(UIP_ETHTYPE_IP);
00405       BUF->hwlen = 6;
00406       BUF->protolen = 4;
00407       BUF->ethhdr.type = HTONS(UIP_ETHTYPE_ARP);
00408 
00409       uip_appdata = &uip_buf[UIP_TCPIP_HLEN + UIP_LLH_LEN];
00410     
00411       uip_len = sizeof(struct arp_hdr);
00412       return;
00413     }
00414 
00415     /* Build an ethernet header. */
00416     memcpy(IPBUF->ethhdr.dest.addr, tabptr->ethaddr.addr, 6);
00417   }
00418   memcpy(IPBUF->ethhdr.src.addr, uip_ethaddr.addr, 6);
00419   
00420   IPBUF->ethhdr.type = HTONS(UIP_ETHTYPE_IP);
00421 
00422   uip_len += sizeof(struct uip_eth_hdr);
00423 }
00424 /*-----------------------------------------------------------------------------------*/
00425 
00426 /** @} */
00427 /** @} */

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