The most likely candidate in such a recent
distro would be iptables. To see whether you
have any kind of packet filtering active do:
iptables -L
as root.
If your output differs from this
Code:
Chain INPUT (policy ACCEPT)
target prot opt source destination
Chain FORWARD (policy ACCEPT)
target prot opt source destination
Chain OUTPUT (policy ACCEPT)
target prot opt source destination
you're likely to be firewalled :)
Cheers,
Tink