Implemented ARP for one IPv4 address

wrapper/connections.c

@@ -39,7 +39,7 @@ void send_there(struct in_addr ip4_addr, unsigned char ttl, unsigned int type, u
 	close(sock);
 }
 
-void send_ipv6(unsigned char *packet, int packet_size)
+void send_raw(unsigned char *packet, int packet_size)
 {
 	struct sockaddr_ll	socket_address;	/* target address */
 	struct ifreq		ifr;		/* interface */

wrapper/process.c

@@ -1,4 +1,5 @@
 #include <net/ethernet.h>
+#include <net/if_arp.h>
 
 #include "wrapper.h"
 #include "translate_ip.h"
@@ -17,13 +18,17 @@ void process_packet(u_char *args, const struct pcap_pkthdr *header, const u_char
 
 	switch (htons(eth->type)) {
 		case ETHERTYPE_IP:
-			printf("\n         IP: 4\n");
+			printf("\n      Proto: IPv4\n");
 			process_packet4(eth, payload);
 			break;
 		case ETHERTYPE_IPV6:
-			printf("\n         IP: 6\n");
+			printf("\n      Proto: IPv6\n");
 			process_packet6(eth, payload);
 			break;
+		case ETHERTYPE_ARP:
+			printf("\n      Proto: ARP\n");
+			process_arp(eth, payload);
+			break;
 		default:
 			printf("\n         IP: unknown (%d/0x%x)\n", htons(eth->type), htons(eth->type));
 			break;
@@ -162,7 +167,7 @@ void process_tcp4(const struct s_ethernet *eth_hdr, struct s_ip4 *ip_hdr, const
 	memcpy(packet + SIZE_ETHERNET + SIZE_IP6, tcp, sizeof(struct s_tcp));
 
 	/* send the wrapped packet back */
-	send_ipv6(packet, packet_size);
+	send_raw(packet, packet_size);
 
 	/* free allocated memory */
 	free(packet);
@@ -261,7 +266,7 @@ void process_udp4(const struct s_ethernet *eth_hdr, struct s_ip4 *ip_hdr, const
 	memcpy(packet + SIZE_ETHERNET + SIZE_IP6, udp, sizeof(struct s_udp));
 
 	/* send the wrapped packet back */
-	send_ipv6(packet, packet_size);
+	send_raw(packet, packet_size);
 
 	/* free allocated memory */
 	free(packet);
@@ -377,12 +382,74 @@ void process_icmp4(const struct s_ethernet *eth_hdr, struct s_ip4 *ip_hdr, const
 	memcpy(packet + SIZE_ETHERNET + SIZE_IP6, icmp, sizeof(struct s_icmp));
 
 	/* send the wrapped packet back */
-	send_ipv6(packet, packet_size);
+	send_raw(packet, packet_size);
 
 	/* free allocated memory */
 	free(packet);
 }
 
+void process_arp(const struct s_ethernet *eth_hdr, const unsigned char *arp_packet)
+{
+	struct s_arp		*arp;		/* ARP request packet */
+	struct s_arp		*arpr;		/* ARP reply packet */
+	struct s_ethernet	*eth;
+	unsigned char		*packet;
+	unsigned short		 packet_size;
+
+	arp = (struct s_arp *) arp_packet;
+
+	/* process only requests */
+	if (htons(arp->opcode) != ARPOP_REQUEST) {
+		printf("==> Not ARP request <==\n");
+		return;
+	}
+
+	/* DEBUG: print source and destination IP addresses */
+	printf("    IP From: %s\n", inet_ntoa(arp->ip_src));
+	printf("    IP   To: %s\n", inet_ntoa(arp->ip_dest));
+	printf("   MAC From: %.2x:%.2x:%.2x:%.2x:%.2x:%.2x\n", arp->mac_src.a, arp->mac_src.b, arp->mac_src.c, arp->mac_src.d, arp->mac_src.e, arp->mac_src.f);
+	printf("   MAC   To: %.2x:%.2x:%.2x:%.2x:%.2x:%.2x\n", arp->mac_dest.a, arp->mac_dest.b, arp->mac_dest.c, arp->mac_dest.d, arp->mac_dest.e, arp->mac_dest.f);
+
+	/* check if this packet is ours */
+	if (memcmp(&ip4addr_wrapsix, &arp->ip_dest, 4)) {
+		printf("==> This packet is not ours! <==\n");
+		return;
+	}
+
+	/* compute the packet size */
+	packet_size = SIZE_ETHERNET + sizeof(struct s_arp);
+
+	/* allocate enough memory */
+	if ((packet = (unsigned char *) malloc(packet_size)) == NULL) {
+		fprintf(stderr, "Fatal Error! Lack of free memory!\n");
+		exit(EXIT_FAILURE);
+	}
+	memset(packet, 0x0, packet_size);
+
+	/* define ethernet header and ARP offsets */
+	eth  = (struct s_ethernet *) packet;
+	arpr = (struct s_arp *) (packet + SIZE_ETHERNET);
+
+	/* assemble the ethernet header */
+	eth->dest = eth_hdr->src;
+	memcpy(&eth->src, mac, sizeof(struct s_mac_addr));
+	eth->type = htons(ETHERTYPE_ARP);
+
+	/* assemble the ARP reply part */
+	arpr->hw	= htons(ARPHRD_ETHER);
+	arpr->proto	= htons(ETHERTYPE_IP);
+	arpr->hw_len	= 0x06;
+	arpr->proto_len	= 0x04;
+	arpr->opcode	= htons(ARPOP_REPLY);
+	arpr->mac_src	= eth->src;
+	arpr->mac_dest	= eth->dest;
+	arpr->ip_src	= ip4addr_wrapsix;
+	arpr->ip_dest	= arp->ip_src;
+
+	/* send ARP reply */
+	send_raw(packet, packet_size);
+}
+
 /*** IPv6 ***/
 void process_packet6(const struct s_ethernet *eth, const unsigned char *packet)
 {
@@ -816,7 +883,7 @@ void process_ndp(const struct s_ethernet *eth_hdr, struct s_ip6 *ip_hdr, unsigne
 	icmp->checksum = checksum_ipv6(ip->ip6_src, ip->ip6_dst, htons(ip->ip6_plen), ip->ip6_nxt, (unsigned char *) icmp);
 
 	/* send the packet */
-	send_ipv6(packet, packet_size);
+	send_raw(packet, packet_size);
 
 	/* free allocated memory */
 	free(packet);

wrapper/wrapper.c

@@ -2,9 +2,10 @@
 #include "storage.h"
 
 struct s_mac_addr *mac;			/* MAC address of the device */
-char *dev;				/* capture device name */
+char		  *dev;			/* capture device name */
-int  dev_index;				/* capture device index */
+int		   dev_index;		/* capture device index */
-struct in_addr *dev_ip;			/* IP address associated with the device */
+struct in_addr	  *dev_ip;		/* IP address associated with the device */
+struct in_addr	   ip4addr_wrapsix;	/* IPv4 address for WrapSix */
 
 /* storage trees */
 jsw_rbtree_t *stg_conn_tcp;
@@ -69,6 +70,9 @@ int main(int argc, char **argv)
 	/* get index of the device */
 	dev_index = get_dev_index(dev);
 
+	/* set the WrapSix IPv4 address */
+	inet_aton("10.0.0.111", &ip4addr_wrapsix);
+
 	/* compile the filter expression */
 	if (pcap_compile(handle, &fp, filter_exp, 0, 0) == -1) {
 		fprintf(stderr, "Couldn't parse filter %s: %s\n", filter_exp, pcap_geterr(handle));

wrapper/wrapper.h

@@ -40,6 +40,19 @@ struct s_ethernet {
         unsigned short		type;	/* 16 b; IP/ARP/RARP/... */
 };
 
+/* ARP structure */
+struct s_arp {
+	unsigned short		hw;		/* 16 b; hardware type [0x0001] */
+	unsigned short		proto;		/* 16 b; protocol type [0x0800] */
+	unsigned char		hw_len;		/*  8 b; length of hardware address in bytes [0x06] */
+	unsigned char		proto_len;	/*  8 b; length of protocol address in bytes [0x04] */
+	unsigned short		opcode;		/* 16 b; operation code: [0x0001] or [0x0002] */
+	struct s_mac_addr	mac_src;	/* 48 b; sender hardware address */
+	struct in_addr		ip_src;		/* 32 b; sender protocol address */
+	struct s_mac_addr	mac_dest;	/* 48 b; target hardware address */
+	struct in_addr		ip_dest;	/* 32 b; target protocol address */
+}__attribute__((__packed__));
+
 /* IPv4 header structure */
 struct s_ip4 {
 	unsigned char	ver_ihl;
@@ -171,6 +184,7 @@ void process_packet4(const struct s_ethernet *eth, const unsigned char *packet);
 void process_tcp4(const struct s_ethernet *eth_hdr, struct s_ip4 *ip_hdr, const unsigned char *payload, unsigned short data_size);
 void process_udp4(const struct s_ethernet *eth_hdr, struct s_ip4 *ip_hdr, const unsigned char *payload, unsigned short data_size);
 void process_icmp4(const struct s_ethernet *eth_hdr, struct s_ip4 *ip_hdr, const unsigned char *payload, unsigned short data_size);
+void process_arp(const struct s_ethernet *eth_hdr, const unsigned char *arp_packet);
 
 void process_packet6(const struct s_ethernet *eth, const unsigned char *packet);
 void process_tcp6(const struct s_ethernet *eth, struct s_ip6 *ip, const unsigned char *payload);
@@ -179,7 +193,7 @@ void process_icmp6(const struct s_ethernet *eth, struct s_ip6 *ip, const unsigne
 void process_ndp(const struct s_ethernet *eth_hdr, struct s_ip6 *ip_hdr, unsigned char *icmp_data);
 
 void send_there(struct in_addr ip4_addr, unsigned char ttl, unsigned int type, unsigned char *payload, unsigned int paylen);
-void send_ipv6(unsigned char *packet, int packet_size);
+void send_raw(unsigned char *packet, int packet_size);
 
 unsigned short checksum(const void *_buf, int len);
 unsigned short checksum_ipv4(struct in_addr ip_src, struct in_addr ip_dest, unsigned short length, unsigned char proto, unsigned char *data);
@@ -191,5 +205,6 @@ extern char		 *dev;			/* capture device name */
 extern int		  dev_index;		/* capture device index */
 extern struct in_addr	 *dev_ip;		/* IP address associated with the device */
 extern struct in6_addr	  ip6addr_wrapsix;	/* IPv6 prefix of WrapSix addresses */
+extern struct in_addr	  ip4addr_wrapsix;	/* IPv4 address for WrapSix */
 
 #endif