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udhcpc6: set hop limit to 1 in emitted raw packets

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Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
This commit is contained in:
Denys Vlasenko 2011-11-07 18:22:06 +01:00
parent 68c5b28156
commit 2b6a6b90cc
1 changed files with 11 additions and 7 deletions
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18
networking/udhcp/d6_packet.c
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@ -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);