2b6a6b90c
Denys Vlasenko
2011-11-07
Subject
udhcpc6: set hop limit to 1 in emitted raw packets
Binary
No binary (build failed)
Architecture & Compiler Flags
—
Build Log
(log yok)
Commit Diff GitHub →
networking/udhcp/d6_packet.c+11 -7
| @@ -92,16 +92,20 @@ int FAST_FUNC d6_send_raw_packet( | |
| /* size, excluding IP header: */ | |
| packet.udp.len = htons(sizeof(struct udphdr) + d6_pkt_size); | |
| packet.ip6.ip6_plen = packet.udp.len; | |
| - | /* UDP checksum skips first four bytes of IP header. |
| - | * IPv6 'hop limit' field should be 0. |
| - | * 'next header' field should be summed as if it is in a different |
| - | * position, therefore we write its value into ip6_hlim: |
| + | /* |
| + | * Someone was smoking weed (at least) while inventing UDP checksumming: |
| + | * UDP checksum skips first four bytes of IPv6 header. |
| + | * 'next header' field should be summed as if it is one more byte |
| + | * to the right, therefore we write its value (IPPROTO_UDP) |
| + | * into ip6_hlim, and its 'real' location remains zero-filled for now. |
| */ | |
| packet.ip6.ip6_hlim = IPPROTO_UDP; | |
| - | packet.udp.check = inet_cksum((uint16_t *)&packet + 2, |
| - | offsetof(struct ip6_udp_d6_packet, data) - 4 + d6_pkt_size); |
| + | packet.udp.check = inet_cksum( |
| + | (uint16_t *)&packet + 2, |
| + | offsetof(struct ip6_udp_d6_packet, data) - 4 + d6_pkt_size |
| + | ); |
| /* fix 'hop limit' and 'next header' after UDP checksumming */ | |
| - | packet.ip6.ip6_hlim = 8; |
| + | packet.ip6.ip6_hlim = 1; /* observed Windows machines to use hlim=1 */ |
| packet.ip6.ip6_nxt = IPPROTO_UDP; | |
| d6_dump_packet(d6_pkt); | |