fw/arp.c (902aa40) - mips_sys · BlinkenArea

arp.c

/* MIPS I system
 * Copyright 2011-2012 Stefan Schuermans <stefan@blinkenarea.org>
 * Copyleft GNU public license V2 or later
 *          http://www.gnu.org/copyleft/gpl.html
 */

#include "arp.h"
#include "config.h"
#include "ethernet.h"
#include "ip.h"
#include "macros.h"
#include "nethelp.h"

// timing parameters
#define ARP_TICKS_MAX        (150) /**< maximum age of ARP table entries
                                        (in 200ms steps) */
#define ARP_NO_MAC_TICKS_MAX  (50) /**< maximum age of ARP table entries
                                        without MAC (in 200ms steps) */
#define ARP_RETRY_TICKS        (8) /**< time after which to retry ARP query
                                        (must be power of 2, in 200ms steps) */

/// ARP table
#define ARP_TAB_FLAG_IN_USE (1)
#define ARP_TAB_FLAG_MAC_OK (2)
struct arp_table
{
  unsigned int flags; /// flags - see constants
  unsigned int ticks; /// age of entry in 200ms steps
  unsigned char mac[6];
  unsigned char ip[4];
} arp_tab[16];

/**
 * @brief send an ARP request
 * @param[in] ip IP address to query MAC for
 */
static void arp_send_request(unsigned char ip[4])
{
  struct arp_packet arp_request;

// build ARP request
  arp_request.arp_hdr.hw_type = htons(0x0001); // ethernet
  arp_request.arp_hdr.proto_type = htons(0x0800); // IP
  arp_request.arp_hdr.hw_len = 0x06; // length of a MAC address
  arp_request.arp_hdr.proto_len = 0x04; // length of an IP address
  arp_request.arp_hdr.op = htons(0x0001); // ARP request
  mac_cpy(arp_request.arp_hdr.src_mac, config_mac.mac); // own MAC
  ip_cpy(arp_request.arp_hdr.src_ip, config_ip.ip); // own IP
  mac_cpy(arp_request.arp_hdr.dest_mac,
          "\xFF\xFF\xFF\xFF\xFF\xFF"); // broadcast MAC
  ip_cpy(arp_request.arp_hdr.dest_ip, ip); // requested IP

// send ARP request
  mac_cpy(arp_request.eth_hdr.dest, arp_request.arp_hdr.dest_mac);
  arp_request.eth_hdr.type = htons(0x0806); // ethernet packet type: ARP
  ethernet_send(&arp_request, sizeof(arp_request));
}

/// initialize
void arp_init(void)
{
  unsigned int i;

// empty ARP table
  for (i = 0; i < count(arp_tab); ++i)
    arp_tab[i].flags = 0;
}

/// tick procedure - call every 200ms
void arp_tick200(void)
{
  unsigned int i;

// increase age of ARP table entires and remove timed out ones
  for (i = 0; i < count(arp_tab); ++i) {
    // entry in use
    if (arp_tab[i].flags & ARP_TAB_FLAG_IN_USE) {
      arp_tab[i].ticks++; // increase age
      // entry has a MAC
      if (arp_tab[i].flags & ARP_TAB_FLAG_MAC_OK) {
        if (arp_tab[i].ticks > ARP_TICKS_MAX) // too old
          arp_tab[i].flags = 0; // remove entry
      }
      // entry does not have a MAC
      else {
        if (arp_tab[i].ticks > ARP_NO_MAC_TICKS_MAX) // too old
          arp_tab[i].flags = 0; // remove entry
        else if ((arp_tab[i].ticks & (ARP_RETRY_TICKS - 1)) == 0) // re-request
          arp_send_request(arp_tab[i].ip);
      }
    }
  }
}

/**
 * @brief process a received ARP packet
 * @param[in] ptr pointer to data of packet
 * @param[in] sz size of packet
 */
void arp_recv(void *ptr, unsigned int sz)
{
  struct arp_packet *arp_pack;

// packet too short
  if (sz < sizeof(struct arp_packet))
    return;

arp_pack = ptr;

// not IP over ethernet
  if (arp_pack->arp_hdr.hw_type != htons(0x0001) || // ethernet
      arp_pack->arp_hdr.proto_type != htons(0x0800) || // IP
      arp_pack->arp_hdr.hw_len != 0x06 || // length of a MAC address
      arp_pack->arp_hdr.proto_len != 0x04) // length of an IP address
    // we do not support other protocols than IP over ethernet
    return;

// source MAC is broadcast MAC -> broken packet / attac -> get lost
  if (arp_pack->arp_hdr.src_mac[0] == 0xFF &&
      arp_pack->arp_hdr.src_mac[1] == 0xFF &&
      arp_pack->arp_hdr.src_mac[2] == 0xFF &&
      arp_pack->arp_hdr.src_mac[3] == 0xFF &&
      arp_pack->arp_hdr.src_mac[4] == 0xFF &&
      arp_pack->arp_hdr.src_mac[5] == 0xFF)
    return;

// ARP request for own IP address
  if (arp_pack->arp_hdr.op == htons(0x0001) && // ARP request
      ip_eq(arp_pack->arp_hdr.dest_ip, config_ip.ip)) { // own IP address
    struct arp_packet arp_reply;

// build ARP reply
    arp_reply.arp_hdr.hw_type = htons(0x0001); // ethernet
    arp_reply.arp_hdr.proto_type = htons(0x0800); // IP
    arp_reply.arp_hdr.hw_len = 0x06; // length of a MAC address
    arp_reply.arp_hdr.proto_len = 0x04; // length of an IP address
    arp_reply.arp_hdr.op = htons(0x0002); // ARP reply
    mac_cpy(arp_reply.arp_hdr.src_mac, config_mac.mac); // own MAC
    ip_cpy(arp_reply.arp_hdr.src_ip, config_ip.ip); // own IP
    mac_cpy(arp_reply.arp_hdr.dest_mac,
            arp_pack->arp_hdr.src_mac); // requestor's MAC
    ip_cpy(arp_reply.arp_hdr.dest_ip,
           arp_pack->arp_hdr.src_ip); // requestor's IP

// send ARP reply
    mac_cpy(arp_reply.eth_hdr.dest,
            arp_reply.arp_hdr.dest_mac); // ethernet destination address
    arp_reply.eth_hdr.type = htons(0x0806); // ethernet packet type: ARP
    ethernet_send(&arp_reply, sizeof(arp_reply));

return;
  }

// ARP reply to own MAC address and own IP address
  if (arp_pack->arp_hdr.op == htons(0x0002) && // ARP reply
      mac_eq(arp_pack->arp_hdr.dest_mac, config_mac.mac) && // own MAC address
      ip_eq(arp_pack->arp_hdr.dest_ip, config_ip.ip)) { // own IP address

// store MAC for IP
    arp_store(arp_pack->arp_hdr.src_ip, arp_pack->arp_hdr.src_mac);

// notify IP
    //  - IP might be waiting for the MAC to transmit a packet
    ip_got_mac(arp_pack->arp_hdr.src_ip, arp_pack->arp_hdr.src_mac);

return;
  }
}

/**
 * @brief look up the MAC for an IP address
 * @param[in] ip IP address to look up
 * @param[out] mac MAC address for this IP address
 * @return 0 in case of success, 1 if the MAC address is unknown
 */
int arp_lookup(unsigned char ip[4], unsigned char mac[6])
{
  unsigned int i, j;

// own IP
  if (ip_eq(ip, config_ip.ip))
    // own IP may not be looked up via ARP
    return 1;

// search IP in ARP tabale
  for (i = 0; i < count(arp_tab); ++i)
    if ((arp_tab[i].flags & ARP_TAB_FLAG_IN_USE) &&
        ip_eq(ip, arp_tab[i].ip))
      break;

// not found
  if (i >= count(arp_tab)) {
    // find a free entry
    for (i = 0; i < count(arp_tab); ++i)
      if (!(arp_tab[i].flags & ARP_TAB_FLAG_IN_USE))
        break;

// no free entry
    if (i >= count(arp_tab)) {
      // find oldest entry
      i = 0;
      for (j = 1; j < count(arp_tab); ++j)
        if (arp_tab[j].ticks > arp_tab[i].ticks )
          i = j;
    }

// set up this entry
    arp_tab[i].flags = ARP_TAB_FLAG_IN_USE;
    arp_tab[i].ticks = 0;
    ip_cpy(arp_tab[i].ip, ip);
  }

// MAC available
  if (arp_tab[i].flags & ARP_TAB_FLAG_MAC_OK) {
    // return MAC and success
    mac_cpy(mac, arp_tab[i].mac);
    return 0;
  }

// send ARP request
  arp_send_request(ip);

// no success yet
  return 1;
}

/**
 * @brief store the MAC for an IP address
 * @param[in] ip IP address to store MAC for
 * @param[out] mac MAC address for this IP address
 */
void arp_store(unsigned char ip[4], unsigned char mac[6])
{
  unsigned int i, j;

// do not store broadcast MAC
  if (mac[0] == 0xFF && mac[1] == 0xFF && mac[2] == 0xFF &&
      mac[3] == 0xFF && mac[4] == 0xFF && mac[5] == 0xFF)
    return;

// do not store link-local broadcast IP
  if (ip[0] == 0xFF && ip[1] == 0xFF && ip[2] == 0xFF && ip[3] == 0xFF)
    return;
  // do not store non-local IPs
  if ((ip[0] & config_ip.mask[0]) != (config_ip.ip[0] & config_ip.mask[0]) ||
      (ip[1] & config_ip.mask[1]) != (config_ip.ip[1] & config_ip.mask[1]) ||
      (ip[2] & config_ip.mask[2]) != (config_ip.ip[2] & config_ip.mask[2]) ||
      (ip[3] & config_ip.mask[3]) != (config_ip.ip[3] & config_ip.mask[3]))
    return;
  // do not store broadcast IP
  if (ip[0] == (config_ip.ip[0] | ~config_ip.mask[0]) &&
      ip[1] == (config_ip.ip[1] | ~config_ip.mask[1]) &&
      ip[2] == (config_ip.ip[2] | ~config_ip.mask[2]) &&
      ip[3] == (config_ip.ip[3] | ~config_ip.mask[3]))
    return;

// search IP in ARP table
  for (i = 0; i < count(arp_tab); ++i) {
    if ((arp_tab[i].flags & ARP_TAB_FLAG_IN_USE) &&
        ip_eq(ip, arp_tab[i].ip))
      break;
  }

// not found
  if (i >= count(arp_tab)) {
    // find a free entry
    for (i = 0; i < count(arp_tab); ++i)
      if (!(arp_tab[i].flags & ARP_TAB_FLAG_IN_USE))
        break;

// set up this entry
    arp_tab[i].flags = ARP_TAB_FLAG_IN_USE;
    arp_tab[i].ticks = 0;
    ip_cpy(arp_tab[i].ip, ip);
  }

// update ARP table entry
  arp_tab[i].flags = ARP_TAB_FLAG_IN_USE | ARP_TAB_FLAG_MAC_OK;
  arp_tab[i].ticks = 0;
  mac_cpy(arp_tab[i].mac, mac);
}

mips_sys

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