+static bool do_decrement_ttl(node_t *source, vpn_packet_t *packet) {
+ uint16_t type = packet->data[12] << 8 | packet->data[13];
+
+ switch (type) {
+ case ETH_P_IP:
+ if(!checklength(source, packet, 14 + 32))
+ return false;
+
+ if(packet->data[22] < 1) {
+ if(packet->data[25] != IPPROTO_ICMP || packet->data[46] != ICMP_TIME_EXCEEDED)
+ route_ipv4_unreachable(source, packet, ICMP_TIME_EXCEEDED, ICMP_EXC_TTL);
+ return false;
+ }
+
+ uint16_t old = packet->data[22] << 8 | packet->data[23];
+ packet->data[22]--;
+ uint16_t new = packet->data[22] << 8 | packet->data[23];
+
+ uint32_t checksum = packet->data[24] << 8 | packet->data[25];
+ checksum += old + (~new & 0xFFFF);
+ while(checksum >> 16)
+ checksum = (checksum & 0xFFFF) + (checksum >> 16);
+ packet->data[24] = checksum >> 8;
+ packet->data[25] = checksum & 0xff;
+
+ return true;
+
+ case ETH_P_IPV6:
+ if(!checklength(source, packet, 14 + 40))
+ return false;
+
+ if(packet->data[21] < 1) {
+ if(packet->data[20] != IPPROTO_ICMPV6 || packet->data[54] != ICMP6_TIME_EXCEEDED)
+ route_ipv6_unreachable(source, packet, ICMP6_TIME_EXCEEDED, ICMP6_TIME_EXCEED_TRANSIT);
+ return false;
+ }
+
+ packet->data[21]--;
+
+ return true;
+
+ default:
+ return true;
+ }
+}
+
+void route(node_t *source, vpn_packet_t *packet) {
+ if(pcap)
+ send_pcap(packet);
+
+ if(forwarding_mode == FMODE_KERNEL && source != myself) {
+ send_packet(myself, packet);
+ return;
+ }
+
+ if(!checklength(source, packet, ether_size))
+ return;
+
+ if(decrement_ttl && source != myself)
+ if(!do_decrement_ttl(source, packet))
+ return;
+