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router.c
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router.c
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#include <queue.h>
#include "skel.h"
#include "time.h"
// 4 sets of 3 digit numbers + 4 dots
#define ADDR_MAXLEN 4*3 + 4
// Will define a size for the arp table equal to the number of
// devices on the network. For a larger newtwork a list could
// be implemented but this works for this homework's purpose
#define ARPT_CAP 6
// Structures for the route table and arp table
// Taken from laboratory 4
struct rtable_entry {
uint32_t prefix;
uint32_t next_hop;
uint32_t mask;
int interface;
};
struct arp_entry {
uint32_t ip;
uint8_t mac[6];
};
//https://www.geeksforgeeks.org/binary-search-tree-set-1-search-and-insertion/
struct bst_node {
struct rtable_entry key;
struct bst_node* left;
struct bst_node* right;
int height;
};
int max(int a, int b)
{
return (a > b)? a : b;
}
int height(struct bst_node *N)
{
if (N == NULL)
return 0;
return N->height;
}
struct bst_node* newNode(struct rtable_entry item)
{
struct bst_node* temp = (struct bst_node*)malloc(sizeof(struct bst_node));
temp->key = item;
temp->left = NULL;
temp->right = NULL;
temp->height = 1;
return temp;
}
struct bst_node *rightRotate(struct bst_node *y)
{
struct bst_node *x = y->left;
struct bst_node *T2 = x->right;
// Perform rotation
x->right = y;
y->left = T2;
// Update heights
y->height = max(height(y->left), height(y->right))+1;
x->height = max(height(x->left), height(x->right))+1;
// Return new root
return x;
}
struct bst_node *leftRotate(struct bst_node *x)
{
struct bst_node *y = x->right;
struct bst_node *T2 = y->left;
// Perform rotation
y->left = x;
x->right = T2;
// Update heights
x->height = max(height(x->left), height(x->right))+1;
y->height = max(height(y->left), height(y->right))+1;
// Return new root
return y;
}
int getBalance(struct bst_node *N)
{
if (N == NULL)
return 0;
return height(N->left) - height(N->right);
}
struct bst_node* insert(struct bst_node* node, struct rtable_entry key)
{
/* If the tree is empty, return a new node */
if (node == NULL)
return newNode(key);
/* Otherwise, recur down the tree */
if (key.prefix < node->key.prefix)
node->left = insert(node->left, key);
else if (key.prefix > node->key.prefix)
node->right = insert(node->right, key);
else
return node;
node->height = 1 + max(height(node->left), height(node->right));
int balance = getBalance(node);
if (balance > 1 && key.prefix < node->left->key.prefix)
return rightRotate(node);
// Right Right Case
if (balance < -1 && key.prefix > node->right->key.prefix)
return leftRotate(node);
// Left Right Case
if (balance > 1 && key.prefix > node->left->key.prefix)
{
node->left = leftRotate(node->left);
return rightRotate(node);
}
// Right Left Case
if (balance < -1 && key.prefix < node->right->key.prefix)
{
node->right = rightRotate(node->right);
return leftRotate(node);
}
/* return the (unchanged) node pointer */
return node;
}
struct bst_node* search(struct bst_node* root, uint32_t key)
{
// Base Cases: root is null or key is present at root
if (root == NULL || root->key.prefix == key)
return root;
// Key is greater than root's key
if (root->key.prefix < key)
return search(root->right, key);
// Key is smaller than root's key
return search(root->left, key);
}
// Converts a string from format b4.b3.b2.b1 to a 32bit unsigned integer
// Eg: str_to_32b("192.1.4.0") = 3221292032
uint32_t str_to_32b(char* str) {
uint8_t b1;
uint8_t b2;
uint8_t b3;
uint8_t b4;
sscanf(str, "%hhu.%hhu.%hhu.%hhu", &b4, &b3, &b2, &b1);
return (b4 << 24) |
(b3 << 16) |
(b2 << 8) | b1;
}
// Stores the input from file fd into rtable as an array of rtable_entry
void read_rtable(struct bst_node **rtable, FILE* fd) {
// Count the number of entries by counting \n characters
// Allocate necessary memory for the entire routing table
struct rtable_entry new_entry;
rewind(fd);
// Declarations used to populate the routing table
char prefix_str[ADDR_MAXLEN];
char nhop_str[ADDR_MAXLEN];
char mask_str[ADDR_MAXLEN];
char interf;
// For each line in fd:
// read formatted string into: Prefix string,
// Next Hop string,
// Mask string,
// Interface char
// add entry to rtable with each address converted to 32b uint
int i;
char* current_line = NULL;
size_t line_limit = 0;
for(i = 0; getline(¤t_line, &line_limit, fd) > 0; i++) {
sscanf(current_line, "%[0-9.] %[0-9.] %[0-9.] %hhd", prefix_str, \
nhop_str, \
mask_str, \
&interf);
new_entry.prefix = str_to_32b(prefix_str);
new_entry.next_hop = str_to_32b(nhop_str);
new_entry.mask = str_to_32b(mask_str);
new_entry.interface = interf;
if(i == 0){
*rtable = insert(*rtable, new_entry);
}
else
*rtable = insert(*rtable, new_entry);
}
}
struct rtable_entry* get_best_route(uint32_t dest_ip, struct bst_node* rtable) {
uint32_t mask;
mask = 0xFFFFFFFF;
struct bst_node* found = NULL;
while(mask != 0){
found = search(rtable, dest_ip & mask);
if(found != NULL)
return &found->key;
mask = mask << 1;
}
return NULL;
}
struct arp_entry* get_arp(uint32_t dest_ip, struct arp_entry* arp_tb, int arp_t_size) {
printf("LOOKING UP %x\n", dest_ip);
for (int i = 0; i < arp_t_size; i++) {
if(arp_tb[i].ip == dest_ip) {
return &arp_tb[i];
}
}
return NULL;
}
// Add a new ARP entry to the ARP table, return the new dimension of the ARP table
int add_to_arptable(struct arp_entry* arp_tb, struct arp_entry* new_arp, int arp_tb_size) {
arp_tb[arp_tb_size] = *new_arp;
// DEBUG
// printf("ADDED ARP MAC: %x:%x:%x:%x:%x:%x\n", arp_tb[arp_tb_size].mac[0], arp_tb[arp_tb_size].mac[1], arp_tb[arp_tb_size].mac[2], arp_tb[arp_tb_size].mac[3], arp_tb[arp_tb_size].mac[4], arp_tb[arp_tb_size].mac[5]);
// printf("ADDED ARP IP : %x\n", arp_tb[arp_tb_size].ip);
return arp_tb_size + 1;
}
void preOrder(struct bst_node *root)
{
if(root != NULL)
{
preOrder(root->left);
printf("%d ", root->key.interface);
preOrder(root->right);
}
}
int main(int argc, char *argv[])
{
packet m;
int rc;
char buf[20];
// Open table input file and create routing table
FILE* fd;
fd = fopen(argv[1], "r");
DIE(fd <= 0, "Failed to open file");
// Routing table init
struct bst_node* rtable = NULL;
read_rtable(&rtable, fd);
// ARP table init
struct arp_entry* arptable = NULL;
int arptable_size;
// Size initially set to zero, future entries will increase it
arptable_size = 0;
arptable = malloc(sizeof(struct arp_entry) * ARPT_CAP);
queue routerQueue;
routerQueue = queue_create();
init(argc - 2, argv + 2);
while (1) {
rc = get_packet(&m);
DIE(rc < 0, "get_message");
struct ether_header *eth_hdr = (struct ether_header *)m.payload;
struct iphdr *ip_hdr = (struct iphdr *)(m.payload + sizeof(struct ether_header));
struct rtable_entry* best_route;
// TODO: CHECK IF PACKAGE IS OF TYPE ICMP ECHO REQUEST
struct icmphdr * icmp_header;
icmp_header = parse_icmp(m.payload);
if(icmp_header != NULL) {
if(ntohl(ip_hdr->daddr) == str_to_32b(get_interface_ip(m.interface)) && icmp_header->type == ICMP_ECHO){
memcpy(eth_hdr->ether_dhost, eth_hdr->ether_shost, 6);
get_interface_mac(m.interface, eth_hdr->ether_shost);
send_icmp(ip_hdr->saddr, ip_hdr->daddr, eth_hdr->ether_shost, eth_hdr->ether_dhost, ICMP_ECHOREPLY, 0, m.interface, icmp_header->un.echo.id, icmp_header->un.echo.sequence);
continue;
}
}
// TODO: CHECK IF PACKAGE IS OF TYPE ARP
struct arp_header *arp_hdr;
arp_hdr = parse_arp(m.payload);
// If ARP packet was meant for this router, send ARP reply
if(arp_hdr != NULL) {
// Check for match on each router interface
// And send reply if packet was meant for this router
for (int j = 0; j < ROUTER_NUM_INTERFACES; j++)
{
// Check if the target was a router interface
if(ntohl(arp_hdr->tpa) == str_to_32b(get_interface_ip(j))){
// If ARP has type REQUEST send this router's MAC
if(ntohs(arp_hdr->op) == ARPOP_REQUEST){
printf("GOT ARP REQUEST FROM: %s\n", inet_ntop(AF_INET, &arp_hdr->spa, buf, 20));
// Send ARP REPLY from this interface
// Set destination mac address to sender
memcpy(eth_hdr->ether_dhost, arp_hdr->sha, 6);
// Add the MAC of this interface to eth_header as source
get_interface_mac(j, eth_hdr->ether_shost);
eth_hdr->ether_type = htons(ETHERTYPE_ARP);
send_arp(arp_hdr->spa, arp_hdr->tpa, eth_hdr, m.interface, htons(ARPOP_REPLY));
printf("SENT ARP REPLY TO: %s\n", inet_ntop(AF_INET, &arp_hdr->spa, buf, 20));
break;
} else if(ntohs(arp_hdr->op) == ARPOP_REPLY) {
if(get_arp(ntohl(arp_hdr->spa), arptable, arptable_size) != NULL){
continue;
}
printf("GOT ARP REPLY FROM: %s\n", inet_ntop(AF_INET, &arp_hdr->spa, buf, 20));
// If ARP has type REPLY there exists a packet in queue to be sent
// Create a new ARP entry, populate and add it to the ARP table
struct arp_entry* new_arp = malloc(sizeof(struct arp_entry));
new_arp->ip = ntohl(arp_hdr->spa);
memcpy(new_arp->mac, arp_hdr->sha, 6);
arptable_size = add_to_arptable(arptable, new_arp, arptable_size);
// Pull original packet from queue
packet* original;
original = (packet*) queue_deq(routerQueue);
struct ether_header *orig_eth_hdr = (struct ether_header *) original->payload;
struct iphdr *orig_ip_hdr = (struct iphdr *)(original->payload + sizeof(struct ether_header));
// Checksum was already verified, last step is to populate the target MAC and send
best_route = get_best_route(ntohl(orig_ip_hdr->daddr), rtable);
memcpy(orig_eth_hdr->ether_dhost, new_arp->mac, 6);
get_interface_mac(best_route->interface, orig_eth_hdr->ether_shost);
send_packet(best_route->interface, original);
free(new_arp);
break;
}
}
}
continue;
}
// TODO: CHECK CHECKSUM
if(ip_checksum(ip_hdr,sizeof(struct iphdr))){
printf("Invalid Checksum\n");
continue;
}
//http://www.firewall.cx/networking-topics/protocols/icmp-protocol/156-icmp-time-exceeded.html#:~:text=The%20ICMP%20%2D%20Time%20exceeded%20message%20is%20generated%20when%20the%20gateway,and%20therefore%20must%20be%20discarded.
// TODO: CHECK TTL
if(ip_hdr->ttl <= 1){
printf("TTL expired\n");
memcpy(eth_hdr->ether_dhost, eth_hdr->ether_shost, 6);
get_interface_mac(m.interface, eth_hdr->ether_shost);
send_icmp_error(ip_hdr->saddr, ip_hdr->daddr, eth_hdr->ether_shost, eth_hdr->ether_dhost, ICMP_TIME_EXCEEDED, 0, m.interface);
continue;
}
//TODO: FIND BEST ROUTE OR SEND ICMP HOST UNREACHABLE
best_route = get_best_route(ntohl(ip_hdr->daddr), rtable);
if(best_route == NULL) {
memcpy(eth_hdr->ether_dhost, eth_hdr->ether_shost, 6);
get_interface_mac(m.interface, eth_hdr->ether_shost);
send_icmp_error(ip_hdr->saddr, ip_hdr->daddr, eth_hdr->ether_shost, eth_hdr->ether_dhost, ICMP_PORT_UNREACH, 0, m.interface);
continue;
}
//TODO: UPDATE TTL
ip_hdr->ttl--;
ip_hdr->check = 0;
ip_hdr->check = ip_checksum(ip_hdr, sizeof(struct iphdr));
//TODO: FIND MATCHING ARP FOR NEXT HOP
struct arp_entry* arp;
arp = get_arp(best_route->next_hop, arptable, arptable_size);
uint32_t test;
test = ntohl(best_route->next_hop);
// If arp is null, the arp table returned no results and an ARP request must be sent
if (arp == NULL) {
printf("NO MAC FOUND FOR %s IN ARP TABLE\n", inet_ntop(AF_INET, &test, buf, 20));
printf("SENDING ARP REQUEST TO: %s FROM %s \n", inet_ntop(AF_INET, &test, buf, 20), get_interface_ip(best_route->interface));
//TODO: IF NO MATCHING ARP FOUND ADD PACKET TO Q AND SEND REQUEST
packet queuePacket = m;
queue_enq(routerQueue, &queuePacket);
// Generate new ethernet header
// source ether addr set to interface MAC
// destination set to broadcast MAC FF:FF:..:FF
// type set to ETHERTYPE_ARP
get_interface_mac(best_route->interface, eth_hdr->ether_shost);
memset(eth_hdr->ether_dhost, 0xFF, 6);
eth_hdr->ether_type = htons(ETHERTYPE_ARP);
// Send the ARP request
send_arp(htonl(best_route->next_hop), htonl(str_to_32b(get_interface_ip(best_route->interface))), eth_hdr, best_route->interface, htons(ARPOP_REQUEST));
continue;
}
memcpy(eth_hdr->ether_dhost, arp->mac, 6);
get_interface_mac(best_route->interface, eth_hdr->ether_shost);
//TODO: FORWARD PACKET TO BEST ROUTE
send_packet(best_route->interface, &m);
}
free(arptable);
free(rtable);
}