This protocol is not a cure-all for the problems associated with NAT.
It does not enable incoming TCP connections through NAT. It allows
incoming UDP packets through NAT, but only through a subset of
existing NAT types. In particular, STUN does not enable incoming UDP
packets through symmetric NATs (defined below), which are common in
large enterprises. STUN's discovery procedures are based on
assumptions on NAT treatment of UDP; such assumptions may prove
invalid down the road as new NAT devices are deployed. STUN does not
work when it is used to obtain an address to communicate with a peer
which happens to be behind the same NAT. STUN does not work when the
STUN server is not in a common shared address realm. For a more
complete discussion of the limitations of STUN, see Section 14.
