First!
download simple port forwarding
install it!
port forward ur port it should be like [25565]
use udp and tcp!
and now! when ur done with that u should download a minecraft smp server/bukkit server!
u download it here http://www.minecraft.net/download
when u downloaded it place it in a folder! and run it!

TO THE FIX !

My Friends Cant Join Why
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allow java thing at firewall! u get it in controlpanel and firewall and enable a program in the firewall! there!
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my world is exploading so i cant join the lag is so laggy!
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u just have to delete the world folder! then u should be able to join
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how do i make a cracked server!
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u just enter server.propertiers in notepad and change online.mode to FALSE and ur friends and u should be able to join!
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to get your question here send me a comment!
Plz Like Diamond Fav Sub!