# uip/uip_arp.c

Go to the documentation of this file.

    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 2006/06/02 23:36:21 adam Exp $
    00058  *
    00059  */
    00060
    00061
    00062 #include "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(uip_ipaddr_cmp(BUF->dipaddr, uip_hostaddr)) {
    00292       /* First, we register the one who made the request in our ARP
    00293          table, since it is likely that we will do more communication
    00294          with this host in the future. */
    00295       uip_arp_update(BUF->sipaddr, &BUF->shwaddr);
    00296
    00297       /* The reply opcode is 2. */
    00298       BUF->opcode = HTONS(2);
    00299
    00300       memcpy(BUF->dhwaddr.addr, BUF->shwaddr.addr, 6);
    00301       memcpy(BUF->shwaddr.addr, uip_ethaddr.addr, 6);
    00302       memcpy(BUF->ethhdr.src.addr, uip_ethaddr.addr, 6);
    00303       memcpy(BUF->ethhdr.dest.addr, BUF->dhwaddr.addr, 6);
    00304
    00305       BUF->dipaddr[0] = BUF->sipaddr[0];
    00306       BUF->dipaddr[1] = BUF->sipaddr[1];
    00307       BUF->sipaddr[0] = uip_hostaddr[0];
    00308       BUF->sipaddr[1] = uip_hostaddr[1];
    00309
    00310       BUF->ethhdr.type = HTONS(UIP_ETHTYPE_ARP);
    00311       uip_len = sizeof(struct arp_hdr);
    00312     }
    00313     break;
    00314   case HTONS(ARP_REPLY):
    00315     /* ARP reply. We insert or update the ARP table if it was meant
    00316        for us. */
    00317     if(uip_ipaddr_cmp(BUF->dipaddr, uip_hostaddr)) {
    00318       uip_arp_update(BUF->sipaddr, &BUF->shwaddr);
    00319     }
    00320     break;
    00321   }
    00322
    00323   return;
    00324 }
    00325 /*-----------------------------------------------------------------------------------*/
    00326 /**
    00327  * Prepend Ethernet header to an outbound IP packet and see if we need
    00328  * to send out an ARP request.
    00329  *
    00330  * This function should be called before sending out an IP packet. The
    00331  * function checks the destination IP address of the IP packet to see
    00332  * what Ethernet MAC address that should be used as a destination MAC
    00333  * address on the Ethernet.
    00334  *
    00335  * If the destination IP address is in the local network (determined
    00336  * by logical ANDing of netmask and our IP address), the function
    00337  * checks the ARP cache to see if an entry for the destination IP
    00338  * address is found. If so, an Ethernet header is prepended and the
    00339  * function returns. If no ARP cache entry is found for the
    00340  * destination IP address, the packet in the uip_buf[] is replaced by
    00341  * an ARP request packet for the IP address. The IP packet is dropped
    00342  * and it is assumed that they higher level protocols (e.g., TCP)
    00343  * eventually will retransmit the dropped packet.
    00344  *
    00345  * If the destination IP address is not on the local network, the IP
    00346  * address of the default router is used instead.
    00347  *
    00348  * When the function returns, a packet is present in the uip_buf[]
    00349  * buffer, and the length of the packet is in the global variable
    00350  * uip_len.
    00351  */
    00352 /*-----------------------------------------------------------------------------------*/
    00353 void
    00354 uip_arp_out(void)
    00355 {
    00356   struct arp_entry *tabptr;
    00357
    00358   /* Find the destination IP address in the ARP table and construct
    00359      the Ethernet header. If the destination IP addres isn't on the
    00360      local network, we use the default router's IP address instead.
    00361
    00362      If not ARP table entry is found, we overwrite the original IP
    00363      packet with an ARP request for the IP address. */
    00364
    00365   /* First check if destination is a local broadcast. */
    00366   if(uip_ipaddr_cmp(IPBUF->destipaddr, broadcast_ipaddr)) {
    00367     memcpy(IPBUF->ethhdr.dest.addr, broadcast_ethaddr.addr, 6);
    00368   } else {
    00369     /* Check if the destination address is on the local network. */
    00370     if(!uip_ipaddr_maskcmp(IPBUF->destipaddr, uip_hostaddr, uip_netmask)) {
    00371       /* Destination address was not on the local network, so we need to
    00372          use the default router's IP address instead of the destination
    00373          address when determining the MAC address. */
    00374       uip_ipaddr_copy(ipaddr, uip_draddr);
    00375     } else {
    00376       /* Else, we use the destination IP address. */
    00377       uip_ipaddr_copy(ipaddr, IPBUF->destipaddr);
    00378     }
    00379
    00380     for(i = 0; i < UIP_ARPTAB_SIZE; ++i) {
    00381       tabptr = &arp_table[i];
    00382       if(uip_ipaddr_cmp(ipaddr, tabptr->ipaddr)) {
    00383         break;
    00384       }
    00385     }
    00386
    00387     if(i == UIP_ARPTAB_SIZE) {
    00388       /* The destination address was not in our ARP table, so we
    00389          overwrite the IP packet with an ARP request. */
    00390
    00391       memset(BUF->ethhdr.dest.addr, 0xff, 6);
    00392       memset(BUF->dhwaddr.addr, 0x00, 6);
    00393       memcpy(BUF->ethhdr.src.addr, uip_ethaddr.addr, 6);
    00394       memcpy(BUF->shwaddr.addr, uip_ethaddr.addr, 6);
    00395
    00396       uip_ipaddr_copy(BUF->dipaddr, ipaddr);
    00397       uip_ipaddr_copy(BUF->sipaddr, uip_hostaddr);
    00398       BUF->opcode = HTONS(ARP_REQUEST); /* ARP request. */
    00399       BUF->hwtype = HTONS(ARP_HWTYPE_ETH);
    00400       BUF->protocol = HTONS(UIP_ETHTYPE_IP);
    00401       BUF->hwlen = 6;
    00402       BUF->protolen = 4;
    00403       BUF->ethhdr.type = HTONS(UIP_ETHTYPE_ARP);
    00404
    00405       uip_appdata = &uip_buf[UIP_TCPIP_HLEN + UIP_LLH_LEN];
    00406
    00407       uip_len = sizeof(struct arp_hdr);
    00408       return;
    00409     }
    00410
    00411     /* Build an ethernet header. */
    00412     memcpy(IPBUF->ethhdr.dest.addr, tabptr->ethaddr.addr, 6);
    00413   }
    00414   memcpy(IPBUF->ethhdr.src.addr, uip_ethaddr.addr, 6);
    00415
    00416   IPBUF->ethhdr.type = HTONS(UIP_ETHTYPE_IP);
    00417
    00418   uip_len += sizeof(struct uip_eth_hdr);
    00419 }
    00420 /*-----------------------------------------------------------------------------------*/
    00421
    00422 /** @} */
    00423 /** @} */