   Nat Punch
  We are currently using a number of methods for NAT traversal within our game, which allows us to connect in the region of 80% of users without the need for port forwarding.What we want suggestions on how to improve this rate.We currently use direct connections, reverse connections and ICE to achieve this success rate.As most of you probably know the problem arises with symmetric routers.Can someone tell me if NAT punching works between a symmetric router and any other type of router provided it is NOT symmetric? So symmetric to full cone or symmetric to port restricted.Thanks for the helpMartyn   
  With symmetric routers, you have to play "guess the port sequence." Which for some routers is not that hard, and for other routers, is almost impossible (if they scramble the external port sequence, for security purposes, explicitly to foil such attempts).In general, symmetric NAT actually breaks the IP protocol, because they break the persistent host/port mapping that IP in general assumes. People who install those routers typically do so because they WANT it to be broken -- they don't want to allow games in the workplace, say. At some point, you have to give up and respect their wishes.;  Thanks for the comments.I understand port prediction can be used on some symmetric routers, but that doesn't answer the question really.What we want to know is can two peers be connected using a NAT punch if one is behind a symmetric router and the other behind another type of router, including port restricted.We know symmetric to symmetric will not work.Thanks;  The problem is getting back in through the symmetric, it doesn't matter what the other end is (including fully open). The base problem is that the relation (inner ip:port <-> outer ip:port) is not invariant between the introducer and the second peer.   