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ntp: set interface index in IP*_PKTINFO when responding

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When a server with multiple interfaces in the same network is sending a
response, setting the ipi_spec_dst/ipi6_addr field of the IP*_PKTINFO
control message selects the source address, but not necessarily the
interface. The packet has the expected source address, but it may be
sent by an interface that doesn't have the address.

Set the ipi_ifindex/ipi6_ifindex field to respond on the same interface
as the request was received from to avoid asymmetries in delay and
timestamping.
This commit is contained in:
Miroslav Lichvar 2018-08-29 10:56:14 +02:00
parent 018977044a
commit 5fc7674e36
1 changed files with 4 additions and 0 deletions
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4
ntp_io.c
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@ -827,6 +827,8 @@ NIO_SendPacket(NTP_Packet *packet, NTP_Remote_Address *remote_addr,
ipi = (struct in_pktinfo *) CMSG_DATA(cmsg);
ipi->ipi_spec_dst.s_addr = htonl(local_addr->ip_addr.addr.in4);
if (local_addr->if_index != INVALID_IF_INDEX)
ipi->ipi_ifindex = local_addr->if_index;
}
#endif
@ -845,6 +847,8 @@ NIO_SendPacket(NTP_Packet *packet, NTP_Remote_Address *remote_addr,
ipi = (struct in6_pktinfo *) CMSG_DATA(cmsg);
memcpy(&ipi->ipi6_addr.s6_addr, &local_addr->ip_addr.addr.in6,
sizeof(ipi->ipi6_addr.s6_addr));
if (local_addr->if_index != INVALID_IF_INDEX)
ipi->ipi6_ifindex = local_addr->if_index;
}
#endif