addresses such as http://192.1204551/ (aka http://192.18.97.71/

aka http://3222430023/.

Do you have a solid reference...?

Nope. I looked too, and couldn't find one.
I agree with your assessment that it probably is not portable.
(Leave it to Microsoft to write an incompatible - if compliant - network library...)

jdporter
The 6th Rule of Perl Club is -- There is no Rule #6.