X-Git-Url: https://tinc-vpn.org/git/browse?p=tinc;a=blobdiff_plain;f=src%2Froute.c;h=6415f0edcf8351eaa67bbc8cebc32045f286a43e;hp=17f1c71a18e13b4f14e988d45e27a4f7f5ef8f16;hb=496f775568873bb769e48ceb644b15ab9f150d62;hpb=b23bf132838156d2fe5a18d50a2b5e068ae18ec3

diff --git a/src/route.c b/src/route.c
index 17f1c71a..6415f0ed 100644
--- a/src/route.c
+++ b/src/route.c
@@ -55,6 +55,8 @@ static const size_t icmp6_size = sizeof(struct icmp6_hdr);
 static const size_t ns_size = sizeof(struct nd_neighbor_solicit);
 static const size_t opt_size = sizeof(struct nd_opt_hdr);
 
+static bool do_decrement_ttl(node_t *source, vpn_packet_t *packet);
+
 #ifndef MAX
 #define MAX(a, b) ((a) > (b) ? (a) : (b))
 #endif
@@ -115,16 +117,16 @@ static void clamp_mss(const node_t *source, const node_t *via, vpn_packet_t *pac
 
 	/* Find TCP header */
 	int start = ether_size;
-	uint16_t type = packet->data[12] << 8 | packet->data[13];
+	uint16_t type = DATA(packet)[12] << 8 | DATA(packet)[13];
 
 	if(type == ETH_P_8021Q) {
 		start += 4;
-		type = packet->data[16] << 8 | packet->data[17];
+		type = DATA(packet)[16] << 8 | DATA(packet)[17];
 	}
 
-	if(type == ETH_P_IP && packet->data[start + 9] == 6)
-		start += (packet->data[start] & 0xf) * 4;
-	else if(type == ETH_P_IPV6 && packet->data[start + 6] == 6)
+	if(type == ETH_P_IP && DATA(packet)[start + 9] == 6)
+		start += (DATA(packet)[start] & 0xf) * 4;
+	else if(type == ETH_P_IPV6 && DATA(packet)[start + 6] == 6)
 		start += 40;
 	else
 		return;
@@ -133,38 +135,38 @@ static void clamp_mss(const node_t *source, const node_t *via, vpn_packet_t *pac
 		return;
 
 	/* Use data offset field to calculate length of options field */
-	int len = ((packet->data[start + 12] >> 4) - 5) * 4;
+	int len = ((DATA(packet)[start + 12] >> 4) - 5) * 4;
 
 	if(packet->len < start + 20 + len)
 		return;
 
 	/* Search for MSS option header */
 	for(int i = 0; i < len;) {
-		if(packet->data[start + 20 + i] == 0)
+		if(DATA(packet)[start + 20 + i] == 0)
 			break;
 
-		if(packet->data[start + 20 + i] == 1) {
+		if(DATA(packet)[start + 20 + i] == 1) {
 			i++;
 			continue;
 		}
 
-		if(i > len - 2 || i > len - packet->data[start + 21 + i])
+		if(i > len - 2 || i > len - DATA(packet)[start + 21 + i])
 			break;
 
-		if(packet->data[start + 20 + i] != 2) {
-			if(packet->data[start + 21 + i] < 2)
+		if(DATA(packet)[start + 20 + i] != 2) {
+			if(DATA(packet)[start + 21 + i] < 2)
 				break;
-			i += packet->data[start + 21 + i];
+			i += DATA(packet)[start + 21 + i];
 			continue;
 		}
 
-		if(packet->data[start + 21] != 4)
+		if(DATA(packet)[start + 21] != 4)
 			break;
 
 		/* Found it */
-		uint16_t oldmss = packet->data[start + 22 + i] << 8 | packet->data[start + 23 + i];
+		uint16_t oldmss = DATA(packet)[start + 22 + i] << 8 | DATA(packet)[start + 23 + i];
 		uint16_t newmss = mtu - start - 20;
-		uint16_t csum = packet->data[start + 16] << 8 | packet->data[start + 17];
+		uint32_t csum = DATA(packet)[start + 16] << 8 | DATA(packet)[start + 17];
 
 		if(oldmss <= newmss)
 			break;
@@ -172,23 +174,25 @@ static void clamp_mss(const node_t *source, const node_t *via, vpn_packet_t *pac
 		logger(DEBUG_TRAFFIC, LOG_INFO, "Clamping MSS of packet from %s to %s to %d", source->name, via->name, newmss);
 
 		/* Update the MSS value and the checksum */
-		packet->data[start + 22 + i] = newmss >> 8;
-		packet->data[start + 23 + i] = newmss & 0xff;
+		DATA(packet)[start + 22 + i] = newmss >> 8;
+		DATA(packet)[start + 23 + i] = newmss & 0xff;
 		csum ^= 0xffff;
-		csum -= oldmss;
+		csum += oldmss ^ 0xffff;
 		csum += newmss;
+		csum = (csum & 0xffff) + (csum >> 16);
+		csum += csum >> 16;
 		csum ^= 0xffff;
-		packet->data[start + 16] = csum >> 8;
-		packet->data[start + 17] = csum & 0xff;
+		DATA(packet)[start + 16] = csum >> 8;
+		DATA(packet)[start + 17] = csum;
 		break;
 	}
 }
 
 static void swap_mac_addresses(vpn_packet_t *packet) {
 	mac_t tmp;
-	memcpy(&tmp, &packet->data[0], sizeof tmp);
-	memcpy(&packet->data[0], &packet->data[6], sizeof tmp);
-	memcpy(&packet->data[6], &tmp, sizeof tmp);
+	memcpy(&tmp, &DATA(packet)[0], sizeof tmp);
+	memcpy(&DATA(packet)[0], &DATA(packet)[6], sizeof tmp);
+	memcpy(&DATA(packet)[6], &tmp, sizeof tmp);
 }
 
 static void age_subnets(void *data) {
@@ -248,6 +252,14 @@ static void learn_mac(mac_t *address) {
 	}
 }
 
+static void broadcast_packet_helper(node_t *source, vpn_packet_t *packet) {
+	if(decrement_ttl && source != myself)
+		if(!do_decrement_ttl(source, packet))
+			return;
+
+	broadcast_packet(source, packet);
+}
+
 /* RFC 792 */
 
 static void route_ipv4_unreachable(node_t *source, vpn_packet_t *packet, length_t ether_size, uint8_t type, uint8_t code) {
@@ -267,13 +279,34 @@ static void route_ipv4_unreachable(node_t *source, vpn_packet_t *packet, length_
 
 	/* Copy headers from packet into properly aligned structs on the stack */
 
-	memcpy(&ip, packet->data + ether_size, ip_size);
+	memcpy(&ip, DATA(packet) + ether_size, ip_size);
 
 	/* Remember original source and destination */
 
 	ip_src = ip.ip_src;
 	ip_dst = ip.ip_dst;
 
+	/* Try to reply with an IP address assigned to the local machine */
+
+	if (type == ICMP_TIME_EXCEEDED && code == ICMP_EXC_TTL) {
+		int sockfd = socket(AF_INET, SOCK_DGRAM, 0);
+		if (sockfd != -1) {
+			struct sockaddr_in addr;
+			memset(&addr, 0, sizeof(addr));
+			addr.sin_family = AF_INET;
+			addr.sin_addr = ip.ip_src;
+			if (!connect(sockfd, (const struct sockaddr*) &addr, sizeof(addr))) {
+				memset(&addr, 0, sizeof(addr));
+				addr.sin_family = AF_INET;
+				socklen_t addrlen = sizeof(addr);
+				if (!getsockname(sockfd, (struct sockaddr*) &addr, &addrlen) && addrlen <= sizeof(addr)) {
+					ip_dst = addr.sin_addr;
+				}
+			}
+			close(sockfd);
+		}
+	}
+
 	oldlen = packet->len - ether_size;
 
 	if(type == ICMP_DEST_UNREACH && code == ICMP_FRAG_NEEDED)
@@ -284,7 +317,7 @@ static void route_ipv4_unreachable(node_t *source, vpn_packet_t *packet, length_
 
 	/* Copy first part of original contents to ICMP message */
 
-	memmove(packet->data + ether_size + ip_size + icmp_size, packet->data + ether_size, oldlen);
+	memmove(DATA(packet) + ether_size + ip_size + icmp_size, DATA(packet) + ether_size, oldlen);
 
 	/* Fill in IPv4 header */
 
@@ -309,12 +342,12 @@ static void route_ipv4_unreachable(node_t *source, vpn_packet_t *packet, length_
 	icmp.icmp_cksum = 0;
 
 	icmp.icmp_cksum = inet_checksum(&icmp, icmp_size, ~0);
-	icmp.icmp_cksum = inet_checksum(packet->data + ether_size + ip_size + icmp_size, oldlen, icmp.icmp_cksum);
+	icmp.icmp_cksum = inet_checksum(DATA(packet) + ether_size + ip_size + icmp_size, oldlen, icmp.icmp_cksum);
 
 	/* Copy structs on stack back to packet */
 
-	memcpy(packet->data + ether_size, &ip, ip_size);
-	memcpy(packet->data + ether_size + ip_size, &icmp, icmp_size);
+	memcpy(DATA(packet) + ether_size, &ip, ip_size);
+	memcpy(DATA(packet) + ether_size + ip_size, &icmp, icmp_size);
 
 	packet->len = ether_size + ip_size + icmp_size + oldlen;
 
@@ -330,8 +363,9 @@ static void fragment_ipv4_packet(node_t *dest, vpn_packet_t *packet, length_t et
 	uint8_t *offset;
 	uint16_t ip_off, origf;
 
-	memcpy(&ip, packet->data + ether_size, ip_size);
+	memcpy(&ip, DATA(packet) + ether_size, ip_size);
 	fragment.priority = packet->priority;
+	fragment.offset = DEFAULT_PACKET_OFFSET;
 
 	if(ip.ip_hl != ip_size / 4)
 		return;
@@ -345,7 +379,7 @@ static void fragment_ipv4_packet(node_t *dest, vpn_packet_t *packet, length_t et
 
 	logger(DEBUG_TRAFFIC, LOG_INFO, "Fragmenting packet of %d bytes to %s (%s)", packet->len, dest->name, dest->hostname);
 
-	offset = packet->data + ether_size + ip_size;
+	offset = DATA(packet) + ether_size + ip_size;
 	maxlen = (dest->mtu - ether_size - ip_size) & ~0x7;
 	ip_off = ntohs(ip.ip_off);
 	origf = ip_off & ~IP_OFFMASK;
@@ -353,7 +387,7 @@ static void fragment_ipv4_packet(node_t *dest, vpn_packet_t *packet, length_t et
 
 	while(todo) {
 		len = todo > maxlen ? maxlen : todo;
-		memcpy(fragment.data + ether_size + ip_size, offset, len);
+		memcpy(DATA(&fragment) + ether_size + ip_size, offset, len);
 		todo -= len;
 		offset += len;
 
@@ -361,8 +395,8 @@ static void fragment_ipv4_packet(node_t *dest, vpn_packet_t *packet, length_t et
 		ip.ip_off = htons(ip_off | origf | (todo ? IP_MF : 0));
 		ip.ip_sum = 0;
 		ip.ip_sum = inet_checksum(&ip, ip_size, ~0);
-		memcpy(fragment.data, packet->data, ether_size);
-		memcpy(fragment.data + ether_size, &ip, ip_size);
+		memcpy(DATA(&fragment), DATA(packet), ether_size);
+		memcpy(DATA(&fragment) + ether_size, &ip, ip_size);
 		fragment.len = ether_size + ip_size + len;
 
 		send_packet(dest, &fragment);
@@ -379,7 +413,7 @@ static void route_ipv4(node_t *source, vpn_packet_t *packet) {
 	node_t *via;
 	ipv4_t dest;
 
-	memcpy(&dest, &packet->data[30], sizeof dest);
+	memcpy(&dest, &DATA(packet)[30], sizeof dest);
 	subnet = lookup_subnet_ipv4(&dest);
 
 	if(!subnet) {
@@ -395,7 +429,7 @@ static void route_ipv4(node_t *source, vpn_packet_t *packet) {
 	}
 
 	if (!subnet->owner) {
-		broadcast_packet(source, packet);
+		broadcast_packet_helper(source, packet);
 		return;
 	}
 
@@ -410,8 +444,12 @@ static void route_ipv4(node_t *source, vpn_packet_t *packet) {
 	if(forwarding_mode == FMODE_OFF && source != myself && subnet->owner != myself)
 		return route_ipv4_unreachable(source, packet, ether_size, ICMP_DEST_UNREACH, ICMP_NET_ANO);
 
+	if(decrement_ttl && source != myself && subnet->owner != myself)
+		if(!do_decrement_ttl(source, packet))
+			return;
+
 	if(priorityinheritance)
-		packet->priority = packet->data[15];
+		packet->priority = DATA(packet)[15];
 
 	via = (subnet->owner->via == myself) ? subnet->owner->nexthop : subnet->owner->via;
 
@@ -425,7 +463,7 @@ static void route_ipv4(node_t *source, vpn_packet_t *packet) {
 
 	if(via && packet->len > MAX(via->mtu, 590) && via != myself) {
 		logger(DEBUG_TRAFFIC, LOG_INFO, "Packet for %s (%s) length %d larger than MTU %d", subnet->owner->name, subnet->owner->hostname, packet->len, via->mtu);
-		if(packet->data[20] & 0x40) {
+		if(DATA(packet)[20] & 0x40) {
 			packet->len = MAX(via->mtu, 590);
 			route_ipv4_unreachable(source, packet, ether_size, ICMP_DEST_UNREACH, ICMP_FRAG_NEEDED);
 		} else {
@@ -445,7 +483,7 @@ static void route_ipv4(node_t *source, vpn_packet_t *packet) {
 static void route_ipv6_unreachable(node_t *source, vpn_packet_t *packet, length_t ether_size, uint8_t type, uint8_t code) {
 	struct ip6_hdr ip6;
 	struct icmp6_hdr icmp6 = {0};
-	uint16_t checksum;
+	uint16_t checksum;	
 
 	struct {
 		struct in6_addr ip6_src;        /* source address */
@@ -463,13 +501,34 @@ static void route_ipv6_unreachable(node_t *source, vpn_packet_t *packet, length_
 
 	/* Copy headers from packet to structs on the stack */
 
-	memcpy(&ip6, packet->data + ether_size, ip6_size);
+	memcpy(&ip6, DATA(packet) + ether_size, ip6_size);
 
 	/* Remember original source and destination */
 
 	pseudo.ip6_src = ip6.ip6_dst;
 	pseudo.ip6_dst = ip6.ip6_src;
 
+	/* Try to reply with an IP address assigned to the local machine */
+
+	if (type == ICMP6_TIME_EXCEEDED && code == ICMP6_TIME_EXCEED_TRANSIT) {
+		int sockfd = socket(AF_INET6, SOCK_DGRAM, 0);
+		if (sockfd != -1) {
+			struct sockaddr_in6 addr;
+			memset(&addr, 0, sizeof(addr));
+			addr.sin6_family = AF_INET6;
+			addr.sin6_addr = ip6.ip6_src;
+			if (!connect(sockfd, (const struct sockaddr*) &addr, sizeof(addr))) {
+				memset(&addr, 0, sizeof(addr));
+				addr.sin6_family = AF_INET6;
+				socklen_t addrlen = sizeof(addr);
+				if (!getsockname(sockfd, (struct sockaddr*) &addr, &addrlen) && addrlen <= sizeof(addr)) {
+					pseudo.ip6_src = addr.sin6_addr;
+				}
+			}
+			close(sockfd);
+		}
+	}
+
 	pseudo.length = packet->len - ether_size;
 
 	if(type == ICMP6_PACKET_TOO_BIG)
@@ -480,7 +539,7 @@ static void route_ipv6_unreachable(node_t *source, vpn_packet_t *packet, length_
 
 	/* Copy first part of original contents to ICMP message */
 
-	memmove(packet->data + ether_size + ip6_size + icmp6_size, packet->data + ether_size, pseudo.length);
+	memmove(DATA(packet) + ether_size + ip6_size + icmp6_size, DATA(packet) + ether_size, pseudo.length);
 
 	/* Fill in IPv6 header */
 
@@ -506,14 +565,14 @@ static void route_ipv6_unreachable(node_t *source, vpn_packet_t *packet, length_
 
 	checksum = inet_checksum(&pseudo, sizeof pseudo, ~0);
 	checksum = inet_checksum(&icmp6, icmp6_size, checksum);
-	checksum = inet_checksum(packet->data + ether_size + ip6_size + icmp6_size, ntohl(pseudo.length) - icmp6_size, checksum);
+	checksum = inet_checksum(DATA(packet) + ether_size + ip6_size + icmp6_size, ntohl(pseudo.length) - icmp6_size, checksum);
 
 	icmp6.icmp6_cksum = checksum;
 
 	/* Copy structs on stack back to packet */
 
-	memcpy(packet->data + ether_size, &ip6, ip6_size);
-	memcpy(packet->data + ether_size + ip6_size, &icmp6, icmp6_size);
+	memcpy(DATA(packet) + ether_size, &ip6, ip6_size);
+	memcpy(DATA(packet) + ether_size + ip6_size, &icmp6, icmp6_size);
 
 	packet->len = ether_size + ip6_size + ntohl(pseudo.length);
 
@@ -526,7 +585,7 @@ static void route_ipv6(node_t *source, vpn_packet_t *packet) {
 	if(!checklength(source, packet, ether_size + ip6_size))
 		return;
 
-	if(packet->data[20] == IPPROTO_ICMPV6 && checklength(source, packet, ether_size + ip6_size + icmp6_size) && packet->data[54] == ND_NEIGHBOR_SOLICIT) {
+	if(DATA(packet)[20] == IPPROTO_ICMPV6 && checklength(source, packet, ether_size + ip6_size + icmp6_size) && DATA(packet)[54] == ND_NEIGHBOR_SOLICIT) {
 		route_neighborsol(source, packet);
 		return;
 	}
@@ -535,7 +594,7 @@ static void route_ipv6(node_t *source, vpn_packet_t *packet) {
 	node_t *via;
 	ipv6_t dest;
 
-	memcpy(&dest, &packet->data[38], sizeof dest);
+	memcpy(&dest, &DATA(packet)[38], sizeof dest);
 	subnet = lookup_subnet_ipv6(&dest);
 
 	if(!subnet) {
@@ -555,7 +614,7 @@ static void route_ipv6(node_t *source, vpn_packet_t *packet) {
 	}
 
 	if (!subnet->owner) {
-		broadcast_packet(source, packet);
+		broadcast_packet_helper(source, packet);
 		return;
 	}
 
@@ -570,6 +629,10 @@ static void route_ipv6(node_t *source, vpn_packet_t *packet) {
 	if(forwarding_mode == FMODE_OFF && source != myself && subnet->owner != myself)
 		return route_ipv6_unreachable(source, packet, ether_size, ICMP6_DST_UNREACH, ICMP6_DST_UNREACH_ADMIN);
 
+	if(decrement_ttl && source != myself && subnet->owner != myself)
+		if(!do_decrement_ttl(source, packet))
+			return;
+
 	via = (subnet->owner->via == myself) ? subnet->owner->nexthop : subnet->owner->via;
 
 	if(via == source) {
@@ -621,15 +684,15 @@ static void route_neighborsol(node_t *source, vpn_packet_t *packet) {
 
 	/* Copy headers from packet to structs on the stack */
 
-	memcpy(&ip6, packet->data + ether_size, ip6_size);
-	memcpy(&ns, packet->data + ether_size + ip6_size, ns_size);
+	memcpy(&ip6, DATA(packet) + ether_size, ip6_size);
+	memcpy(&ns, DATA(packet) + ether_size + ip6_size, ns_size);
 	if(has_opt)
-		memcpy(&opt, packet->data + ether_size + ip6_size + ns_size, opt_size);
+		memcpy(&opt, DATA(packet) + ether_size + ip6_size + ns_size, opt_size);
 
 	/* First, snatch the source address from the neighbor solicitation packet */
 
 	if(overwrite_mac)
-		memcpy(mymac.x, packet->data + ETH_ALEN, ETH_ALEN);
+		memcpy(mymac.x, DATA(packet) + ETH_ALEN, ETH_ALEN);
 
 	/* Check if this is a valid neighbor solicitation request */
 
@@ -655,7 +718,7 @@ static void route_neighborsol(node_t *source, vpn_packet_t *packet) {
 	checksum = inet_checksum(&ns, ns_size, checksum);
 	if(has_opt) {
 		checksum = inet_checksum(&opt, opt_size, checksum);
-		checksum = inet_checksum(packet->data + ether_size + ip6_size + ns_size + opt_size, ETH_ALEN, checksum);
+		checksum = inet_checksum(DATA(packet) + ether_size + ip6_size + ns_size + opt_size, ETH_ALEN, checksum);
 	}
 
 	if(checksum) {
@@ -686,16 +749,20 @@ static void route_neighborsol(node_t *source, vpn_packet_t *packet) {
 	if(subnet->owner == myself)
 		return;                                          /* silently ignore */
 
+	if(decrement_ttl)
+		if(!do_decrement_ttl(source, packet))
+			return;
+
 	/* Create neighbor advertation reply */
 
-	memcpy(packet->data, packet->data + ETH_ALEN, ETH_ALEN); /* copy destination address */
-	packet->data[ETH_ALEN * 2 - 1] ^= 0xFF;                  /* mangle source address so it looks like it's not from us */
+	memcpy(DATA(packet), DATA(packet) + ETH_ALEN, ETH_ALEN); /* copy destination address */
+	DATA(packet)[ETH_ALEN * 2 - 1] ^= 0xFF;                  /* mangle source address so it looks like it's not from us */
 
 	ip6.ip6_dst = ip6.ip6_src;                               /* swap destination and source protocoll address */
 	ip6.ip6_src = ns.nd_ns_target;
 
 	if(has_opt)
-		memcpy(packet->data + ether_size + ip6_size + ns_size + opt_size, packet->data + ETH_ALEN, ETH_ALEN);   /* add fake source hard addr */
+		memcpy(DATA(packet) + ether_size + ip6_size + ns_size + opt_size, DATA(packet) + ETH_ALEN, ETH_ALEN);   /* add fake source hard addr */
 
 	ns.nd_ns_cksum = 0;
 	ns.nd_ns_type = ND_NEIGHBOR_ADVERT;
@@ -718,17 +785,17 @@ static void route_neighborsol(node_t *source, vpn_packet_t *packet) {
 	checksum = inet_checksum(&ns, ns_size, checksum);
 	if(has_opt) {
 		checksum = inet_checksum(&opt, opt_size, checksum);
-		checksum = inet_checksum(packet->data + ether_size + ip6_size + ns_size + opt_size, ETH_ALEN, checksum);
+		checksum = inet_checksum(DATA(packet) + ether_size + ip6_size + ns_size + opt_size, ETH_ALEN, checksum);
 	}
 
 	ns.nd_ns_hdr.icmp6_cksum = checksum;
 
 	/* Copy structs on stack back to packet */
 
-	memcpy(packet->data + ether_size, &ip6, ip6_size);
-	memcpy(packet->data + ether_size + ip6_size, &ns, ns_size);
+	memcpy(DATA(packet) + ether_size, &ip6, ip6_size);
+	memcpy(DATA(packet) + ether_size + ip6_size, &ns, ns_size);
 	if(has_opt)
-		memcpy(packet->data + ether_size + ip6_size + ns_size, &opt, opt_size);
+		memcpy(DATA(packet) + ether_size + ip6_size + ns_size, &opt, opt_size);
 
 	send_packet(source, packet);
 }
@@ -751,11 +818,11 @@ static void route_arp(node_t *source, vpn_packet_t *packet) {
 	/* First, snatch the source address from the ARP packet */
 
 	if(overwrite_mac)
-		memcpy(mymac.x, packet->data + ETH_ALEN, ETH_ALEN);
+		memcpy(mymac.x, DATA(packet) + ETH_ALEN, ETH_ALEN);
 
 	/* Copy headers from packet to structs on the stack */
 
-	memcpy(&arp, packet->data + ether_size, arp_size);
+	memcpy(&arp, DATA(packet) + ether_size, arp_size);
 
 	/* Check if this is a valid ARP request */
 
@@ -781,20 +848,22 @@ static void route_arp(node_t *source, vpn_packet_t *packet) {
 	if(subnet->owner == myself)
 		return;                                          /* silently ignore */
 
-	memcpy(packet->data, packet->data + ETH_ALEN, ETH_ALEN); /* copy destination address */
-	packet->data[ETH_ALEN * 2 - 1] ^= 0xFF;                  /* mangle source address so it looks like it's not from us */
+	if(decrement_ttl)
+		if(!do_decrement_ttl(source, packet))
+			return;
 
 	memcpy(&addr, arp.arp_tpa, sizeof addr);                 /* save protocol addr */
 	memcpy(arp.arp_tpa, arp.arp_spa, sizeof addr);           /* swap destination and source protocol address */
 	memcpy(arp.arp_spa, &addr, sizeof addr);                 /* ... */
 
 	memcpy(arp.arp_tha, arp.arp_sha, ETH_ALEN);              /* set target hard/proto addr */
-	memcpy(arp.arp_sha, packet->data + ETH_ALEN, ETH_ALEN);  /* add fake source hard addr */
+	memcpy(arp.arp_sha, DATA(packet) + ETH_ALEN, ETH_ALEN);  /* set source hard/proto addr */
+	arp.arp_sha[ETH_ALEN - 1] ^= 0xFF;                       /* for consistency with route_packet() */
 	arp.arp_op = htons(ARPOP_REPLY);
 
 	/* Copy structs on stack back to packet */
 
-	memcpy(packet->data + ether_size, &arp, arp_size);
+	memcpy(DATA(packet) + ether_size, &arp, arp_size);
 
 	send_packet(source, packet);
 }
@@ -807,17 +876,17 @@ static void route_mac(node_t *source, vpn_packet_t *packet) {
 
 	if(source == myself) {
 		mac_t src;
-		memcpy(&src, &packet->data[6], sizeof src);
+		memcpy(&src, &DATA(packet)[6], sizeof src);
 		learn_mac(&src);
 	}
 
 	/* Lookup destination address */
 
-	memcpy(&dest, &packet->data[0], sizeof dest);
+	memcpy(&dest, &DATA(packet)[0], sizeof dest);
 	subnet = lookup_subnet_mac(NULL, &dest);
 
 	if(!subnet || !subnet->owner) {
-		broadcast_packet(source, packet);
+		broadcast_packet_helper(source, packet);
 		return;
 	}
 
@@ -829,10 +898,14 @@ static void route_mac(node_t *source, vpn_packet_t *packet) {
 	if(forwarding_mode == FMODE_OFF && source != myself && subnet->owner != myself)
 		return;
 
-	uint16_t type = packet->data[12] << 8 | packet->data[13];
+	if(decrement_ttl && source != myself && subnet->owner != myself)
+		if(!do_decrement_ttl(source, packet))
+			return;
+
+	uint16_t type = DATA(packet)[12] << 8 | DATA(packet)[13];
 
 	if(priorityinheritance && type == ETH_P_IP && packet->len >= ether_size + ip_size)
-		packet->priority = packet->data[15];
+		packet->priority = DATA(packet)[15];
 
 	// Handle packets larger than PMTU
 
@@ -846,12 +919,12 @@ static void route_mac(node_t *source, vpn_packet_t *packet) {
 		length_t ethlen = 14;
 
 		if(type == ETH_P_8021Q) {
-			type = packet->data[16] << 8 | packet->data[17];
+			type = DATA(packet)[16] << 8 | DATA(packet)[17];
 			ethlen += 4;
 		}
 
 		if(type == ETH_P_IP && packet->len > 576 + ethlen) {
-			if(packet->data[6 + ethlen] & 0x40) {
+			if(DATA(packet)[6 + ethlen] & 0x40) {
 				packet->len = via->mtu;
 				route_ipv4_unreachable(source, packet, ethlen, ICMP_DEST_UNREACH, ICMP_FRAG_NEEDED);
 			} else {
@@ -883,16 +956,16 @@ static void send_pcap(vpn_packet_t *packet) {
 			len = c->outmaclength;
 
 		if(send_request(c, "%d %d %d", CONTROL, REQ_PCAP, len))
-			send_meta(c, (char *)packet->data, len);
+			send_meta(c, (char *)DATA(packet), len);
 	}
 }
 
 static bool do_decrement_ttl(node_t *source, vpn_packet_t *packet) {
-	uint16_t type = packet->data[12] << 8 | packet->data[13];
+	uint16_t type = DATA(packet)[12] << 8 | DATA(packet)[13];
 	length_t ethlen = ether_size;
 
 	if(type == ETH_P_8021Q) {
-		type = packet->data[16] << 8 | packet->data[17];
+		type = DATA(packet)[16] << 8 | DATA(packet)[17];
 		ethlen += 4;
 	}
 
@@ -901,22 +974,22 @@ static bool do_decrement_ttl(node_t *source, vpn_packet_t *packet) {
 			if(!checklength(source, packet, ethlen + ip_size))
 				return false;
 
-			if(packet->data[ethlen + 8] < 1) {
-				if(packet->data[ethlen + 11] != IPPROTO_ICMP || packet->data[ethlen + 32] != ICMP_TIME_EXCEEDED)
+			if(DATA(packet)[ethlen + 8] <= 1) {
+				if(DATA(packet)[ethlen + 11] != IPPROTO_ICMP || DATA(packet)[ethlen + 32] != ICMP_TIME_EXCEEDED)
 					route_ipv4_unreachable(source, packet, ethlen, ICMP_TIME_EXCEEDED, ICMP_EXC_TTL);
 				return false;
 			}
 
-			uint16_t old = packet->data[ethlen + 8] << 8 | packet->data[ethlen + 9];
-			packet->data[ethlen + 8]--;
-			uint16_t new = packet->data[ethlen + 8] << 8 | packet->data[ethlen + 9];
+			uint16_t old = DATA(packet)[ethlen + 8] << 8 | DATA(packet)[ethlen + 9];
+			DATA(packet)[ethlen + 8]--;
+			uint16_t new = DATA(packet)[ethlen + 8] << 8 | DATA(packet)[ethlen + 9];
 
-			uint32_t checksum = packet->data[ethlen + 10] << 8 | packet->data[ethlen + 11];
+			uint32_t checksum = DATA(packet)[ethlen + 10] << 8 | DATA(packet)[ethlen + 11];
 			checksum += old + (~new & 0xFFFF);
 			while(checksum >> 16)
 				checksum = (checksum & 0xFFFF) + (checksum >> 16);
-			packet->data[ethlen + 10] = checksum >> 8;
-			packet->data[ethlen + 11] = checksum & 0xff;
+			DATA(packet)[ethlen + 10] = checksum >> 8;
+			DATA(packet)[ethlen + 11] = checksum & 0xff;
 
 			return true;
 
@@ -924,13 +997,13 @@ static bool do_decrement_ttl(node_t *source, vpn_packet_t *packet) {
 			if(!checklength(source, packet, ethlen + ip6_size))
 				return false;
 
-			if(packet->data[ethlen + 7] < 1) {
-				if(packet->data[ethlen + 6] != IPPROTO_ICMPV6 || packet->data[ethlen + 40] != ICMP6_TIME_EXCEEDED)
+			if(DATA(packet)[ethlen + 7] <= 1) {
+				if(DATA(packet)[ethlen + 6] != IPPROTO_ICMPV6 || DATA(packet)[ethlen + 40] != ICMP6_TIME_EXCEEDED)
 					route_ipv6_unreachable(source, packet, ethlen, ICMP6_TIME_EXCEEDED, ICMP6_TIME_EXCEED_TRANSIT);
 				return false;
 			}
 
-			packet->data[ethlen + 7]--;
+			DATA(packet)[ethlen + 7]--;
 
 			return true;
 
@@ -951,11 +1024,7 @@ void route(node_t *source, vpn_packet_t *packet) {
 	if(!checklength(source, packet, ether_size))
 		return;
 
-	if(decrement_ttl && source != myself)
-		if(!do_decrement_ttl(source, packet))
-			return;
-
-	uint16_t type = packet->data[12] << 8 | packet->data[13];
+	uint16_t type = DATA(packet)[12] << 8 | DATA(packet)[13];
 
 	switch (routing_mode) {
 		case RMODE_ROUTER:
@@ -983,7 +1052,7 @@ void route(node_t *source, vpn_packet_t *packet) {
 			break;
 
 		case RMODE_HUB:
-			broadcast_packet(source, packet);
+			broadcast_packet_helper(source, packet);
 			break;
 	}
 }