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https://code.semirocket.science/wrapsix
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Fragmenting of too big TCPv4 packets
This commit is contained in:
Michal Zima
parent
32deb4f0ee
commit
b28566bc64
13
src/ipv6.h
13
src/ipv6.h
@ -21,6 +21,8 @@
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#include "ethernet.h" /* s_ethernet */
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#define IPV6_FLAG_MORE_FRAGMENTS 0x0001
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/* IPv6 address structure */
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struct s_ipv6_addr {
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unsigned char addr[16];
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@ -38,6 +40,17 @@ struct s_ipv6 {
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struct s_ipv6_addr ip_dest; /* 128 b; destination address */
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} __attribute__ ((__packed__));
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/* IPv6 fragment header structure */
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struct s_ipv6_fragment {
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unsigned char next_header; /* 8 b; next header */
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unsigned char zeros; /* 8 b; reserved */
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unsigned short offset_flag; /* 13 b; fragment offset in B,
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2 b; reserved,
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1 b; flag */
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unsigned int id; /* 32 b; id of the packet
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(for fragmentation) */
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} __attribute__ ((__packed__));
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/* IPv6 pseudoheader structure for checksum */
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struct s_ipv6_pseudo {
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struct s_ipv6_addr ip_src; /* 128 b; source address */
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195
src/tcp.c
195
src/tcp.c
@ -52,78 +52,149 @@ int tcp_ipv4(struct s_ethernet *eth4, struct s_ipv4 *ip4, char *payload,
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unsigned short orig_checksum;
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unsigned char *packet;
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struct s_ethernet *eth6;
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struct s_ipv6 *ip6;
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struct s_ethernet *eth6;
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struct s_ipv6 *ip6;
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struct s_ipv6_fragment *frag;
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/* parse TCP header */
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tcp = (struct s_tcp *) payload;
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/* full processing of unfragmented packet or the first fragment with
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* TCP header with checksum field (this is safe)
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*/
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if ((ip4->flags_offset & htons(IPV4_FLAG_DONT_FRAGMENT)) ||
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((ip4->flags_offset & htons(IPV4_FLAG_MORE_FRAGMENTS)) &&
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(ip4->flags_offset & 0xff1f) == 0x0000 &&
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payload_size >= sizeof(struct s_tcp) - 2)) {
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/* parse TCP header */
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tcp = (struct s_tcp *) payload;
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/* checksum recheck */
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if (tcp->checksum != 0x0000) {
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orig_checksum = tcp->checksum;
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tcp->checksum = 0;
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tcp->checksum = checksum_ipv4(ip4->ip_src, ip4->ip_dest,
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payload_size, IPPROTO_TCP,
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(unsigned char *) tcp);
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/* checksum recheck -- only if the packet is unfragmented */
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if ((ip4->flags_offset | htons(IPV4_FLAG_DONT_FRAGMENT)) ==
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htons(IPV4_FLAG_DONT_FRAGMENT)) {
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orig_checksum = tcp->checksum;
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tcp->checksum = 0;
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tcp->checksum = checksum_ipv4(ip4->ip_src, ip4->ip_dest,
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payload_size, IPPROTO_TCP,
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(unsigned char *) tcp);
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if (tcp->checksum != orig_checksum) {
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/* packet is corrupted and shouldn't be processed */
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printf("[Debug] Wrong checksum\n");
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if (tcp->checksum != orig_checksum) {
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/* packet is corrupted and shouldn't be
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* processed */
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printf("[Debug] Wrong checksum\n");
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return 1;
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}
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}
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/* find connection in NAT */
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connection = nat_in(nat4_tcp, ip4->ip_src,
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tcp->port_src, tcp->port_dest);
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if (connection == NULL) {
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printf("[Debug] Incoming connection wasn't found in "
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"NAT\n");
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return 1;
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}
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}
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/* find connection in NAT */
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connection = nat_in(nat4_tcp, ip4->ip_src, tcp->port_src, tcp->port_dest);
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/* allocate enough memory for translated packet */
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if ((packet = (unsigned char *) malloc(
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payload_size > MTU - sizeof(struct s_ipv6) ?
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MTU + sizeof(struct s_ethernet) :
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sizeof(struct s_ethernet) + sizeof(struct s_ipv6) +
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payload_size)) == NULL) {
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fprintf(stderr, "[Error] Lack of free memory\n");
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return 1;
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}
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eth6 = (struct s_ethernet *) packet;
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ip6 = (struct s_ipv6 *) (packet + sizeof(struct s_ethernet));
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if (connection == NULL) {
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printf("[Debug] Incoming connection wasn't found in NAT\n");
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/* build ethernet header */
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eth6->dest = connection->mac;
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eth6->src = mac;
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eth6->type = htons(ETHERTYPE_IPV6);
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/* build IPv6 header */
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ip6->ver = 0x60 | (ip4->tos >> 4);
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ip6->traffic_class = ip4->tos << 4;
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ip6->flow_label = 0x0;
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ip6->hop_limit = ip4->ttl;
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ipv4_to_ipv6(&ip4->ip_src, &ip6->ip_src);
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memcpy(&ip6->ip_dest, &connection->ipv6,
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sizeof(struct s_ipv6_addr));
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/* set incoming source port */
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tcp->port_dest = connection->ipv6_port_src;
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/* compute TCP checksum */
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tcp->checksum = checksum_ipv6_update(tcp->checksum,
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ip4->ip_src, ip4->ip_dest,
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connection->ipv4_port_src,
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ip6->ip_src, ip6->ip_dest,
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connection->ipv6_port_src);
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/* fragment it or not? */
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if (payload_size > MTU - sizeof(struct s_ipv6)) {
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/* 1st fragments' payload size must be 8-byte aligned */
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#define FRAGMENT_LEN (((MTU - sizeof(struct s_ipv6) - \
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sizeof(struct s_ipv6_fragment)) / 8) * 8)
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/* fill in missing IPv6 header fields */
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ip6->len = htons(FRAGMENT_LEN +
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sizeof(struct s_ipv6_fragment));
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ip6->next_header = IPPROTO_FRAGMENT;
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/* create IPv6 fragment header */
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frag = (struct s_ipv6_fragment *) ((unsigned char *) ip6
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+ sizeof(struct s_ipv6));
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frag->next_header = IPPROTO_TCP;
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frag->zeros = 0x0;
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frag->offset_flag = htons(IPV6_FLAG_MORE_FRAGMENTS);
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frag->id = ip4->id ? htonl(htons(ip4->id)) :
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(unsigned int) rand();
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/* copy the payload data */
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memcpy((unsigned char *) frag +
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sizeof(struct s_ipv6_fragment),
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payload, FRAGMENT_LEN);
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/* send translated packet */
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transmit_raw(packet, sizeof(struct s_ethernet) +
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sizeof(struct s_ipv6) +
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sizeof(struct s_ipv6_fragment) +
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FRAGMENT_LEN);
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/* create the second fragment */
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ip6->len = htons(payload_size +
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sizeof(struct s_ipv6_fragment) -
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FRAGMENT_LEN);
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frag->offset_flag = htons((FRAGMENT_LEN / 8) << 3);
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/* copy the payload data */
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memcpy((unsigned char *) frag +
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sizeof(struct s_ipv6_fragment),
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payload + FRAGMENT_LEN,
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payload_size - FRAGMENT_LEN);
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/* send translated packet */
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transmit_raw(packet, sizeof(struct s_ethernet) +
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sizeof(struct s_ipv6) +
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sizeof(struct s_ipv6_fragment) -
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FRAGMENT_LEN + payload_size);
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} else {
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ip6->len = htons(payload_size);
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ip6->next_header = IPPROTO_TCP;
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/* copy the payload data */
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memcpy((unsigned char *) ip6 + sizeof(struct s_ipv6),
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payload, payload_size);
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/* send translated packet */
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transmit_raw(packet, sizeof(struct s_ethernet) +
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sizeof(struct s_ipv6) + payload_size);
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}
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} else {
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/* TODO: handle all fragments */
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printf("[Debug] Can't handle fragments :c(\n");
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return 1;
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}
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/* allocate memory for translated packet */
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if ((packet = (unsigned char *) malloc(sizeof(struct s_ethernet) +
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sizeof(struct s_ipv6) +
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payload_size)) == NULL) {
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fprintf(stderr, "[Error] Lack of free memory\n");
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return 1;
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}
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eth6 = (struct s_ethernet *) packet;
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ip6 = (struct s_ipv6 *) (packet + sizeof(struct s_ethernet));
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/* build ethernet header */
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eth6->dest = connection->mac;
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eth6->src = mac;
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eth6->type = htons(ETHERTYPE_IPV6);
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/* build IPv6 packet */
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ip6->ver = 0x60;
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ip6->traffic_class = 0x0;
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ip6->flow_label = 0x0;
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ip6->len = htons(payload_size);
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ip6->next_header = IPPROTO_TCP;
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ip6->hop_limit = ip4->ttl;
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ipv4_to_ipv6(&ip4->ip_src, &ip6->ip_src);
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memcpy(&ip6->ip_dest, &connection->ipv6, sizeof(struct s_ipv6_addr));
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/* set incoming source port */
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tcp->port_dest = connection->ipv6_port_src;
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/* compute TCP checksum */
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tcp->checksum = checksum_ipv6_update(tcp->checksum,
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ip4->ip_src, ip4->ip_dest,
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connection->ipv4_port_src,
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ip6->ip_src, ip6->ip_dest,
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connection->ipv6_port_src);
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/* copy the payload data (with new checksum) */
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memcpy(packet + sizeof(struct s_ethernet) + sizeof(struct s_ipv6),
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payload, payload_size);
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/* send translated packet */
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transmit_raw(packet, sizeof(struct s_ethernet) + sizeof(struct s_ipv6) +
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payload_size);
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/* clean-up */
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free(packet);
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@ -22,6 +22,8 @@
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#include "ipv4.h"
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#include "ipv6.h"
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#define MTU 1280
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extern struct ifreq interface;
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extern struct s_mac_addr mac;
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extern struct s_ipv6_addr ndp_multicast_addr;
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