[erader]

How can I see by who is a server flooded ?

[8088]

You can recognise them by the hose or empty buckets in their hands.

What kind of floods? Which operating system?

[erader]

Linux.

I think the server is flooded with a fake client method cause you can see the player in spectator list but it doesn't have a ip.

[pillepallus]

try iptables (paketfilter) and activate logging. there u will find all connection related details.