How can we create a BSD socket that binds on ., PortX and udp46?

Question

abhishekjain OP

Created Dec ’23

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One: does it involve below or any other steps?

Create a socket (AF_INET6, SOCK_DGRAM, IPPROTO_UDP)
Bind it to AF_INET6, in6addr_any, port X.
Disable IPV6_V6ONLY using setsockopt.

Second: If answer to above is yes, in other operating system, if a datagram would have got received over IPv4, it would have lead to IPv4-mapped IPv6 address in the recvfrom call and protocol would have been considered udp6.

Third: is UDP46 only supported by Apple Kernel (is it not a POSIX standard behaviour) and also within Apple Kernel - not supported on all versions?

Why this question? We created a NWListener on a local port, using udp and when we ran a 'netstat -an -p udp', it showed protocol as 'udp46'

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Answer 1

DTS Engineer OP

Apple

Dec ’23

I’m much less familiar with this for UDP than I am for TCP. In TCP, support for unified IPv4 and IPv6 sockets is not an Apple addition but was inherited from our base BSD Sockets implementation, KAME [1]. I expect that the same is true for UDP.

Also, RFC 3493 has explicit affordance for this sort thing; Check out section 3.7 Compatibility with IPv4 Nodes.

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[1] https://www.kame.net

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How can we create a BSD socket that binds on *.*, PortX and udp46?

How can we create a BSD socket that binds on ., PortX and udp46?