In Network.Socket:socket, the IPv6Only socket option is set to 0 so that both IPv4 and IPv6 can be handled with one socket, when the address family is AF_INET6. This is not always desired, and some parameters cause an exception to be raised.

For example, ICMPv6 (protocol number 58) is a protocol that is specifically for IPv6. The issue can be reproduced in GHCi on Linux as follows:

> import Network.Socket
> sock <- socket AF_INET6 Raw 58
*** Exception: setSocketOption: invalid argument (Invalid argument)

The code already suppresses setSocketOption errors on Windows platforms. A simple fix would be to do so on all platforms, and I am preparing a pull request for this. Personally, I feel that it would be preferable to not set the option in socket, especially since its appropriateness is application-specific and will likely change as IPv4 becomes less prominent.