/*---------------------------------------------------------------------
* Method: handle_outgoing_icmp
*
* Scope: Global
*
* This function contains the logic for handling outbound ICMP packets.
* in concludes the appropriate response to take, either to route, drop
* or generate a host unreachable ICMP error. It also translates the
* outgoing packet if necessary. The router will then implements the NAT's
* recommendation on the potentially modified ip packet.
*
* parameters:
* sr - a reference to the router structure
* iphdr - a struct containing the NAT's translation policy
*
*---------------------------------------------------------------------*/
nat_action_type handle_outgoing_icmp(struct sr_instance *sr, sr_ip_hdr_t *iphdr)
{
DebugNAT("+++ NAT handling outbound ICMP +++\n");
struct sr_nat *nat = &sr->nat;
unsigned int iplen = ntohs(iphdr->ip_len);
unsigned int icmplen = 0;
sr_icmp_echo_hdr_t *icmphdr = (sr_icmp_echo_hdr_t *) extract_ip_payload(iphdr, iplen, &icmplen);
if ((icmphdr->icmp_type != icmp_type_echoreply) &&
(icmphdr->icmp_type != icmp_type_echoreq)) {
DebugNAT("+++ Unsupported ICMP type. +++\n");
return nat_action_drop; //ignore icmp packets other then echo requests/replies
}
uint32_t ip_src = iphdr->ip_src;
//uint32_t ip_dst = ntohl(iphdr->ip_dst);
uint16_t aux_src = icmphdr->icmp_id;
sr_nat_mapping_t *map = sr_nat_lookup_internal(nat,ip_src,aux_src,nat_mapping_icmp);
if (map == NULL) {
//insert new mapping into the translation table
map = sr_nat_insert_mapping(sr,ip_src,aux_src,0,0,nat_mapping_icmp);
DebugNAT("+++ Created NAT mapping from id [%d] to [%d]. +++\n",ntohs(map->aux_int),ntohs(map->aux_ext));
}
//translate entry
translate_outgoing_icmp(iphdr,map);
//update connection state
update_icmp_connection(map);
return nat_action_route;
}
/**
* ICMP Echo reply (on receipt of an ICMP Echo request to one of the router’s interfaces)
*/
int nat_icmp(uint8_t* buf, unsigned int len, struct sr_instance* sr,
char* interface) {
//sr_ethernet_hdr_t *p_ehdr = (sr_ethernet_hdr_t *) buf;
sr_ip_hdr_t* p_iphdr = (sr_ip_hdr_t *) (buf + sizeof(sr_ethernet_hdr_t));
struct icmphdr* p_icmphdr = (struct icmphdr*) ((uint8_t *) p_iphdr
+ 4 * (p_iphdr->ip_hl & 0x0f));
/**
check sum verify, temporary set the chksum part to 0
*/
uint16_t lenIcmp = ntohs(p_iphdr->ip_len) - (p_iphdr->ip_hl & 0x0f) * 4;
uint16_t calculatedsum = cksum(p_icmphdr, lenIcmp);
if (calculatedsum + 1 != 0x010000) {
printf("icmp sum check fails: %d, length: %d\n", calculatedsum,
lenIcmp);
return -1;
}
printf("[icmp nat]icmp sum check pass\n");
//printf("------------------> %d, %d\n", ICMP_ECHOREPLY , p_icmphdr->type &0x0ff);
if (p_icmphdr->type == ICMP_ECHO) {
printf("[icmp nat info] get the request, start to nat forwarding, ip: %d, id: %d\n",ntohl(p_iphdr->ip_src), ntohs(p_icmphdr->un.echo.id));
/* if the echo request come from external network, drop it */
if (memcmp(if_nat->name, interface, strlen(if_nat->name)) != 0) {
printf(
"[warning] echo request comes from external network, drop it. source interface: %s\n",
interface);
return 1;
}
/* looking up the mapping entry, or insert a new one */
struct sr_nat_mapping *m = sr_nat_lookup_internal(&(sr->nat),
ntohl(p_iphdr->ip_src), ntohs(p_icmphdr->un.echo.id),
nat_mapping_icmp);
if (m == NULL ) {
printf("[echo id: %d]\n", ntohs(p_icmphdr->un.echo.id));
m = sr_nat_insert_mapping(&(sr->nat), ntohl(p_iphdr->ip_src),
ntohs(p_icmphdr->un.echo.id), ntohl(p_iphdr->ip_dst),nat_mapping_icmp, 0, 0);
printf("[nat-------------------------------------------------] insert new nat icmp entry, now table: \n");
print_mapping_table(sr->nat.mappings);
}
assert(m);
/* rewrite the package */
p_icmphdr->un.echo.id = htons(m->aux_ext);
sr_nat_update_icmp_mapping(&(sr->nat), p_icmphdr->un.echo.id);
p_icmphdr->checksum = 0;
p_icmphdr->checksum = cksum(p_icmphdr, lenIcmp);
struct in_addr dest;
//dest.s_addr = ntohl(pIpHdr->ip_dst);
dest.s_addr =( p_iphdr->ip_dst);
struct sr_rt *tSr = sr_find_routing_entry(sr, dest, buf, len);
printf("[nat icmp] find exit interface: %s\n", tSr->interface);
printf("[nat icmp] --------------find the out ip for destination ip: ");
printf("destinate: ");
print_ip_int(dest.s_addr);
printf("\n");
uint32_t ipOut = find_ip_by_interface(tSr->interface, sr->if_list);
printf("interface: %s , exit ip ", tSr->interface);
print_ip_int(ipOut);
printf("\n");
p_iphdr->ip_src = ipOut;
sr_forward_ippacket(sr, buf, len);
printf("[nat] forward a icmp request, [id= %d]\n", m->aux_ext);
free(m);
return 0;
} else if (ICMP_ECHOREPLY == (p_icmphdr->type & 0x0ff)) {
printf("get icmp response from ");
print_ip_int(ntohl(p_iphdr->ip_src));
printf("\n");
struct sr_nat_mapping *m = sr_nat_lookup_external(&(sr->nat),
ntohs(p_icmphdr->un.echo.id), nat_mapping_icmp);
if (NULL == m) {
printf("unknown icmp reply [id = %d ], drop it\n",
ntohs(p_icmphdr->un.echo.id));
return 1;
}
/* rewrite the icmp header */
p_icmphdr->un.echo.id = htons(m->aux_int);
p_icmphdr->checksum = 0;
p_icmphdr->checksum = cksum(p_icmphdr, lenIcmp);
// printf("[nat] ----------------\n");
// print_ip_int(p_iphdr->ip_dst);
// printf("[nat] ----------------\n");
// print_ip_int(m->ip_int);
// printf("[nat] ----------------\n");
/*rewrite the dst ip */
p_iphdr->ip_dst = htonl(m->ip_int);
sr_forward_ippacket(sr, buf, len);
sr_nat_update_icmp_mapping(&(sr->nat), p_icmphdr->un.echo.id);
free(m);
return 0;
} else {
printf("[nat icmp]get other type of icmp packet, type(%d), ignore\n",
p_icmphdr->type & 0x0ff);
return 0;
}
//return 1;
}
// New NAT handling function
void processNatIP(struct sr_instance *sr, uint8_t *packet, unsigned int len, struct sr_if *interface){
sr_ip_hdr_t *ipHeader = (sr_ip_hdr_t *) (packet + ethernetHeaderSize);
uint8_t protocolType = ipHeader->ip_p;
if (protocolType == TCP){
// Create the tcp header and print it
//TODO:sr_tcp_hdr_t *tcpHeader = (sr_tcp_hdr_t *) (packet + sizeof(sr_ethernet_hdr_t) + (ipHeader->ip_hl * 4));
//TODO: Need to Update the port and Update the checksum
}
if (protocolType == ICMP){
// If the interface name matches the internal nat interface
if (!strncmp(interface->name, internalNat, sr_IFACE_NAMELEN)) {
/* received from internal interface */
// Check if this this router is the destination
struct sr_if *destination = getIpInterface(sr, ipHeader->ip_dst);
// If the destination is not for us, handle it with ICMP
if (destination != NULL) {
processICMP(sr, packet, len);
}
// Otherwise, if the destination is not for us, need to forward it
else {
/* outbound */
// Construct Type 0 ICMP Header
sr_icmp_t0_hdr_t *icmpHeader = (sr_icmp_t0_hdr_t *) (packet + ethernetHeaderSize + (ipHeader->ip_hl * 4));
// Look up the mapping associated with given internal ip port pair
struct sr_nat_mapping *natMapping = sr_nat_lookup_internal(&(sr->nat), ipHeader->ip_src, icmpHeader->icmp_id, nat_mapping_icmp);
// No such nat mapping => insert into the mapping list
if (!natMapping) {
natMapping = sr_nat_insert_mapping(&(sr->nat), ipHeader->ip_src, icmpHeader->icmp_id, nat_mapping_icmp);
}
// Get external Nat Interface
struct sr_if *externalNatInterface = sr_get_interface(sr, externalNat);
/* Update the ICMP and IP Header */
ipHeader->ip_src = externalNatInterface->ip;
ipHeader->ip_sum = 0;
ipHeader->ip_sum = cksum(ipHeader, ipHeader->ip_hl * 4);
icmpHeader->icmp_id = natMapping->aux_ext;
icmpHeader->icmp_sum = 0;
icmpHeader->icmp_sum = cksum(icmpHeader, ntohs(ipHeader->ip_len) - (ipHeader->ip_hl * 4));
free(natMapping);
// Forward th IP
ipForwarding(sr, packet, len);
}
}
// Otherwise: if the interface name does match external nat interface
else if (!strncmp(interface->name, externalNat, sr_IFACE_NAMELEN)) {
/* received from external interface */
// Check the destination
struct sr_if *destination = getIpInterface(sr, ipHeader->ip_dst);
// If the destination isn't for us, just drop it
if (destination == NULL) {
return;
}
// If the destination is for us: Same behaviour
else {
/* inbound */
sr_icmp_t0_hdr_t *icmpHeader = (sr_icmp_t0_hdr_t *)(packet + ethernetHeaderSize + (ipHeader->ip_hl * 4));
struct sr_nat_mapping *natMapping = sr_nat_lookup_external(&(sr->nat), icmpHeader->icmp_id, nat_mapping_icmp);
if (!natMapping) {
return;
}
/* Update the ICMP and IP Header */
ipHeader->ip_dst = natMapping->ip_int;
ipHeader->ip_sum = 0;
ipHeader->ip_sum = cksum(ipHeader, ipHeader->ip_hl * 4);
icmpHeader->icmp_id = natMapping->aux_int;
icmpHeader->icmp_sum = 0;
icmpHeader->icmp_sum = cksum(icmpHeader, ntohs(ipHeader->ip_len) - (ipHeader->ip_hl * 4));
free(natMapping);
ipForwarding(sr, packet, len);
}
}
}
}