//called if icmp packet comes in
void icmp_packet_in(char *buffer,unsigned int len) {
int i;
//we only support ICMP echo request (ping) packets:
if (buffer[ICMP_POS_TYPE] == ICMP_TYPE_ECHO_REQUEST) {
//reuse buffer for the ICMP echo reply:
//*******************************
//setup the eth packet:
for(i=0; i<6; i++)
buffer[i] = buffer[6+i];
//packet source mac:
nic_copy_mac_to_buf(&buffer[6]);
//change type to ECHO REPLY
buffer[ICMP_POS_TYPE] = ICMP_TYPE_ECHO_REPLY;
//"calculate" checksum:
//use quick & dirty hack, we change only the icmp type
//so we can calculate the new checksum like this:
if (buffer[ICMP_POS_CHECKSUM+0] > 0xFF-0x08)
buffer[ICMP_POS_CHECKSUM+1] = buffer[ICMP_POS_CHECKSUM+1] + 1;
buffer[ICMP_POS_CHECKSUM+0] = buffer[ICMP_POS_CHECKSUM+0] + 0x08;
//set up dst ip (copy src to dest ip):
for(i=0; i<4; i++) {
buffer[IP_POS_DST_IP+i] = buffer[IP_POS_SRC_IP+i];
}
//set up src ip:
nic_ip_to_buffer(&buffer[IP_POS_SRC_IP], nic_ip);
nic_send_packet(buffer,len);
}
}
// Lab 6 network dirver
// Return number of data sent
int
sys_net_send(void *buf, size_t size)
{
return nic_send_packet(buf, size);
}