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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 1.8 2010/12/14 22:45:22 dak664 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   uint16_t hwtype;
00069   uint16_t protocol;
00070   uint8_t hwlen;
00071   uint8_t protolen;
00072   uint16_t opcode;
00073   struct uip_eth_addr shwaddr;
00074   uip_ipaddr_t sipaddr;
00075   struct uip_eth_addr dhwaddr;
00076   uip_ipaddr_t dipaddr;
00077 };
00078 
00079 struct ethip_hdr {
00080   struct uip_eth_hdr ethhdr;
00081   /* IP header. */
00082   uint8_t vhl,
00083     tos,
00084     len[2],
00085     ipid[2],
00086     ipoffset[2],
00087     ttl,
00088     proto;
00089   uint16_t ipchksum;
00090   uip_ipaddr_t srcipaddr, destipaddr;
00091 };
00092 
00093 #define ARP_REQUEST 1
00094 #define ARP_REPLY   2
00095 
00096 #define ARP_HWTYPE_ETH 1
00097 
00098 struct arp_entry {
00099   uip_ipaddr_t ipaddr;
00100   struct uip_eth_addr ethaddr;
00101   uint8_t time;
00102 };
00103 
00104 static const struct uip_eth_addr broadcast_ethaddr =
00105   {{0xff,0xff,0xff,0xff,0xff,0xff}};
00106 static const uint16_t broadcast_ipaddr[2] = {0xffff,0xffff};
00107 
00108 static struct arp_entry arp_table[UIP_ARPTAB_SIZE];
00109 static uip_ipaddr_t ipaddr;
00110 static uint8_t i, c;
00111 
00112 static uint8_t arptime;
00113 static uint8_t tmpage;
00114 
00115 #define BUF   ((struct arp_hdr *)&uip_buf[0])
00116 #define IPBUF ((struct ethip_hdr *)&uip_buf[0])
00117 
00118 #define DEBUG 0
00119 #if DEBUG
00120 #include <stdio.h>
00121 #define PRINTF(...) printf(__VA_ARGS__)
00122 #else
00123 #define PRINTF(...)
00124 #endif
00125 
00126 /*-----------------------------------------------------------------------------------*/
00127 /**
00128  * Initialize the ARP module.
00129  *
00130  */
00131 /*-----------------------------------------------------------------------------------*/
00132 void
00133 uip_arp_init(void)
00134 {
00135   for(i = 0; i < UIP_ARPTAB_SIZE; ++i) {
00136     memset(&arp_table[i].ipaddr, 0, 4);
00137   }
00138 }
00139 /*-----------------------------------------------------------------------------------*/
00140 /**
00141  * Periodic ARP processing function.
00142  *
00143  * This function performs periodic timer processing in the ARP module
00144  * and should be called at regular intervals. The recommended interval
00145  * is 10 seconds between the calls.
00146  *
00147  */
00148 /*-----------------------------------------------------------------------------------*/
00149 void
00150 uip_arp_timer(void)
00151 {
00152   struct arp_entry *tabptr;
00153   
00154   ++arptime;
00155   for(i = 0; i < UIP_ARPTAB_SIZE; ++i) {
00156     tabptr = &arp_table[i];
00157     if(uip_ipaddr_cmp(&tabptr->ipaddr, &uip_all_zeroes_addr) &&
00158        arptime - tabptr->time >= UIP_ARP_MAXAGE) {
00159       memset(&tabptr->ipaddr, 0, 4);
00160     }
00161   }
00162 
00163 }
00164 
00165 /*-----------------------------------------------------------------------------------*/
00166 static void
00167 uip_arp_update(uip_ipaddr_t *ipaddr, struct uip_eth_addr *ethaddr)
00168 {
00169   register struct arp_entry *tabptr = arp_table;
00170 
00171   /* Walk through the ARP mapping table and try to find an entry to
00172      update. If none is found, the IP -> MAC address mapping is
00173      inserted in the ARP table. */
00174   for(i = 0; i < UIP_ARPTAB_SIZE; ++i) {
00175     tabptr = &arp_table[i];
00176 
00177     /* Only check those entries that are actually in use. */
00178     if(!uip_ipaddr_cmp(&tabptr->ipaddr, &uip_all_zeroes_addr)) {
00179 
00180       /* Check if the source IP address of the incoming packet matches
00181          the IP address in this ARP table entry. */
00182       if(uip_ipaddr_cmp(ipaddr, &tabptr->ipaddr)) {
00183          
00184         /* An old entry found, update this and return. */
00185         memcpy(tabptr->ethaddr.addr, ethaddr->addr, 6);
00186         tabptr->time = arptime;
00187 
00188         return;
00189       }
00190     }
00191         tabptr++;
00192   }
00193 
00194   /* If we get here, no existing ARP table entry was found, so we
00195      create one. */
00196 
00197   /* First, we try to find an unused entry in the ARP table. */
00198   for(i = 0; i < UIP_ARPTAB_SIZE; ++i) {
00199     tabptr = &arp_table[i];
00200     if(uip_ipaddr_cmp(&tabptr->ipaddr, &uip_all_zeroes_addr)) {
00201       break;
00202     }
00203   }
00204 
00205   /* If no unused entry is found, we try to find the oldest entry and
00206      throw it away. */
00207   if(i == UIP_ARPTAB_SIZE) {
00208     tmpage = 0;
00209     c = 0;
00210     for(i = 0; i < UIP_ARPTAB_SIZE; ++i) {
00211       tabptr = &arp_table[i];
00212       if(arptime - tabptr->time > tmpage) {
00213         tmpage = arptime - tabptr->time;
00214         c = i;
00215       }
00216     }
00217     i = c;
00218     tabptr = &arp_table[i];
00219   }
00220 
00221   /* Now, i is the ARP table entry which we will fill with the new
00222      information. */
00223   uip_ipaddr_copy(&tabptr->ipaddr, ipaddr);
00224   memcpy(tabptr->ethaddr.addr, ethaddr->addr, 6);
00225   tabptr->time = arptime;
00226 }
00227 /*-----------------------------------------------------------------------------------*/
00228 /**
00229  * ARP processing for incoming IP packets
00230  *
00231  * This function should be called by the device driver when an IP
00232  * packet has been received. The function will check if the address is
00233  * in the ARP cache, and if so the ARP cache entry will be
00234  * refreshed. If no ARP cache entry was found, a new one is created.
00235  *
00236  * This function expects an IP packet with a prepended Ethernet header
00237  * in the uip_buf[] buffer, and the length of the packet in the global
00238  * variable uip_len.
00239  */
00240 /*-----------------------------------------------------------------------------------*/
00241 #if 0
00242 void
00243 uip_arp_ipin(void)
00244 {
00245   uip_len -= sizeof(struct uip_eth_hdr);
00246         
00247   /* Only insert/update an entry if the source IP address of the
00248      incoming IP packet comes from a host on the local network. */
00249   if((IPBUF->srcipaddr[0] & uip_netmask[0]) !=
00250      (uip_hostaddr[0] & uip_netmask[0])) {
00251     return;
00252   }
00253   if((IPBUF->srcipaddr[1] & uip_netmask[1]) !=
00254      (uip_hostaddr[1] & uip_netmask[1])) {
00255     return;
00256   }
00257   uip_arp_update(IPBUF->srcipaddr, &(IPBUF->ethhdr.src));
00258   
00259   return;
00260 }
00261 #endif /* 0 */
00262 /*-----------------------------------------------------------------------------------*/
00263 /**
00264  * ARP processing for incoming ARP packets.
00265  *
00266  * This function should be called by the device driver when an ARP
00267  * packet has been received. The function will act differently
00268  * depending on the ARP packet type: if it is a reply for a request
00269  * that we previously sent out, the ARP cache will be filled in with
00270  * the values from the ARP reply. If the incoming ARP packet is an ARP
00271  * request for our IP address, an ARP reply packet is created and put
00272  * into the uip_buf[] buffer.
00273  *
00274  * When the function returns, the value of the global variable uip_len
00275  * indicates whether the device driver should send out a packet or
00276  * not. If uip_len is zero, no packet should be sent. If uip_len is
00277  * non-zero, it contains the length of the outbound packet that is
00278  * present in the uip_buf[] buffer.
00279  *
00280  * This function expects an ARP packet with a prepended Ethernet
00281  * header in the uip_buf[] buffer, and the length of the packet in the
00282  * global variable uip_len.
00283  */
00284 /*-----------------------------------------------------------------------------------*/
00285 void
00286 uip_arp_arpin(void)
00287 {
00288   
00289   if(uip_len < sizeof(struct arp_hdr)) {
00290     uip_len = 0;
00291     return;
00292   }
00293   uip_len = 0;
00294   
00295   switch(BUF->opcode) {
00296   case UIP_HTONS(ARP_REQUEST):
00297     /* ARP request. If it asked for our address, we send out a
00298        reply. */
00299     /*    if(BUF->dipaddr[0] == uip_hostaddr[0] &&
00300           BUF->dipaddr[1] == uip_hostaddr[1]) {*/
00301     PRINTF("uip_arp_arpin: request for %d.%d.%d.%d (we are %d.%d.%d.%d)\n",
00302            BUF->dipaddr.u8[0], BUF->dipaddr.u8[1],
00303            BUF->dipaddr.u8[2], BUF->dipaddr.u8[3],
00304            uip_hostaddr.u8[0], uip_hostaddr.u8[1],
00305            uip_hostaddr.u8[2], uip_hostaddr.u8[3]);
00306     if(uip_ipaddr_cmp(&BUF->dipaddr, &uip_hostaddr)) {
00307       /* First, we register the one who made the request in our ARP
00308          table, since it is likely that we will do more communication
00309          with this host in the future. */
00310       uip_arp_update(&BUF->sipaddr, &BUF->shwaddr);
00311       
00312       BUF->opcode = UIP_HTONS(ARP_REPLY);
00313 
00314       memcpy(BUF->dhwaddr.addr, BUF->shwaddr.addr, 6);
00315       memcpy(BUF->shwaddr.addr, uip_ethaddr.addr, 6);
00316       memcpy(BUF->ethhdr.src.addr, uip_ethaddr.addr, 6);
00317       memcpy(BUF->ethhdr.dest.addr, BUF->dhwaddr.addr, 6);
00318       
00319       uip_ipaddr_copy(&BUF->dipaddr, &BUF->sipaddr);
00320       uip_ipaddr_copy(&BUF->sipaddr, &uip_hostaddr);
00321 
00322       BUF->ethhdr.type = UIP_HTONS(UIP_ETHTYPE_ARP);
00323       uip_len = sizeof(struct arp_hdr);
00324     }
00325     break;
00326   case UIP_HTONS(ARP_REPLY):
00327     /* ARP reply. We insert or update the ARP table if it was meant
00328        for us. */
00329     if(uip_ipaddr_cmp(&BUF->dipaddr, &uip_hostaddr)) {
00330       uip_arp_update(&BUF->sipaddr, &BUF->shwaddr);
00331     }
00332     break;
00333   }
00334 
00335   return;
00336 }
00337 /*-----------------------------------------------------------------------------------*/
00338 /**
00339  * Prepend Ethernet header to an outbound IP packet and see if we need
00340  * to send out an ARP request.
00341  *
00342  * This function should be called before sending out an IP packet. The
00343  * function checks the destination IP address of the IP packet to see
00344  * what Ethernet MAC address that should be used as a destination MAC
00345  * address on the Ethernet.
00346  *
00347  * If the destination IP address is in the local network (determined
00348  * by logical ANDing of netmask and our IP address), the function
00349  * checks the ARP cache to see if an entry for the destination IP
00350  * address is found. If so, an Ethernet header is prepended and the
00351  * function returns. If no ARP cache entry is found for the
00352  * destination IP address, the packet in the uip_buf[] is replaced by
00353  * an ARP request packet for the IP address. The IP packet is dropped
00354  * and it is assumed that they higher level protocols (e.g., TCP)
00355  * eventually will retransmit the dropped packet.
00356  *
00357  * If the destination IP address is not on the local network, the IP
00358  * address of the default router is used instead.
00359  *
00360  * When the function returns, a packet is present in the uip_buf[]
00361  * buffer, and the length of the packet is in the global variable
00362  * uip_len.
00363  */
00364 /*-----------------------------------------------------------------------------------*/
00365 void
00366 uip_arp_out(void)
00367 {
00368   struct arp_entry *tabptr = arp_table;
00369   
00370   /* Find the destination IP address in the ARP table and construct
00371      the Ethernet header. If the destination IP addres isn't on the
00372      local network, we use the default router's IP address instead.
00373 
00374      If not ARP table entry is found, we overwrite the original IP
00375      packet with an ARP request for the IP address. */
00376 
00377   /* First check if destination is a local broadcast. */
00378   if(uip_ipaddr_cmp(&IPBUF->destipaddr, &uip_broadcast_addr)) {
00379     memcpy(IPBUF->ethhdr.dest.addr, broadcast_ethaddr.addr, 6);
00380   } else if(IPBUF->destipaddr.u8[0] == 224) {
00381     /* Multicast. */
00382     IPBUF->ethhdr.dest.addr[0] = 0x01;
00383     IPBUF->ethhdr.dest.addr[1] = 0x00;
00384     IPBUF->ethhdr.dest.addr[2] = 0x5e;
00385     IPBUF->ethhdr.dest.addr[3] = IPBUF->destipaddr.u8[1];
00386     IPBUF->ethhdr.dest.addr[4] = IPBUF->destipaddr.u8[2];
00387     IPBUF->ethhdr.dest.addr[5] = IPBUF->destipaddr.u8[3];
00388   } else {
00389     /* Check if the destination address is on the local network. */
00390     if(!uip_ipaddr_maskcmp(&IPBUF->destipaddr, &uip_hostaddr, &uip_netmask)) {
00391       /* Destination address was not on the local network, so we need to
00392          use the default router's IP address instead of the destination
00393          address when determining the MAC address. */
00394       uip_ipaddr_copy(&ipaddr, &uip_draddr);
00395     } else {
00396       /* Else, we use the destination IP address. */
00397       uip_ipaddr_copy(&ipaddr, &IPBUF->destipaddr);
00398     }
00399     for(i = 0; i < UIP_ARPTAB_SIZE; ++i) {
00400       if(uip_ipaddr_cmp(&ipaddr, &tabptr->ipaddr)) {
00401         break;
00402       }
00403           tabptr++;
00404     }
00405 
00406     if(i == UIP_ARPTAB_SIZE) {
00407       /* The destination address was not in our ARP table, so we
00408          overwrite the IP packet with an ARP request. */
00409 
00410       memset(BUF->ethhdr.dest.addr, 0xff, 6);
00411       memset(BUF->dhwaddr.addr, 0x00, 6);
00412       memcpy(BUF->ethhdr.src.addr, uip_ethaddr.addr, 6);
00413       memcpy(BUF->shwaddr.addr, uip_ethaddr.addr, 6);
00414     
00415       uip_ipaddr_copy(&BUF->dipaddr, &ipaddr);
00416       uip_ipaddr_copy(&BUF->sipaddr, &uip_hostaddr);
00417       BUF->opcode = UIP_HTONS(ARP_REQUEST); /* ARP request. */
00418       BUF->hwtype = UIP_HTONS(ARP_HWTYPE_ETH);
00419       BUF->protocol = UIP_HTONS(UIP_ETHTYPE_IP);
00420       BUF->hwlen = 6;
00421       BUF->protolen = 4;
00422       BUF->ethhdr.type = UIP_HTONS(UIP_ETHTYPE_ARP);
00423 
00424       uip_appdata = &uip_buf[UIP_TCPIP_HLEN + UIP_LLH_LEN];
00425     
00426       uip_len = sizeof(struct arp_hdr);
00427       return;
00428     }
00429 
00430     /* Build an ethernet header. */
00431     memcpy(IPBUF->ethhdr.dest.addr, tabptr->ethaddr.addr, 6);
00432   }
00433   memcpy(IPBUF->ethhdr.src.addr, uip_ethaddr.addr, 6);
00434   
00435   IPBUF->ethhdr.type = UIP_HTONS(UIP_ETHTYPE_IP);
00436 
00437   uip_len += sizeof(struct uip_eth_hdr);
00438 }
00439 /*-----------------------------------------------------------------------------------*/
00440 
00441 /** @} */
00442 /** @} */
00443