Hi,
I know that linux networking stack is dual-stack. I can send/receive to
both IPv4 and IPv6 addresses with an IPv6 socket using send, sendto,
recvfrom, etc. For IPv4 addresses, I simply convert to IPv4-mapped IPv6
address when populating sockaddr_in6.
Theoretically, I can specify the source address of the outgoing packet
on an IPv6 socket by using sendmsg with IPV6_PKTINFO option enabled and
in6_pktinfo. However, I cannot do this when the source address I specify
is IPv4-mapped. The system still chooses the IPv4 source based on the
routing table. Does linux IPv6 support IPv4-mapped addresses for
sendmsg? Note I do not have trouble with the destination IPv4-mapped
address in the destination sockaddr_in6 structure.
My own guess is no because IPv6 is not as tightly integrated as it
seems, linux dual-stack is a bit odd. Yes, I can send and receive IPv4
packets via IPv4-mapped addresses. But consider this example.
If I have enabled IPV6_PKTINFO on an IPv6 socket, I would expect to
receive both IPv6 and IPv4 local address (as IPv4-mapped address) info
in an in6_pktinfo when using recvmsg. But I only receive data for IPv6
packets. To receive IPv4 local address info from an IPv4 incoming
packet, I have to also enable IP_PKTINFO on the IPv6 socket.
Furthermore, the data will be a regular IPv4 address in an in_pktinfo
structure.
Chinh
--
http://www.certicom.com
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