NAT Type

Discussion in 'General Discussion' started by wency, Sep 11, 2006.

  1. wency

    wency Network Guru Member

    Hello, sometimes i need to use SIP phones and phone adapters sitting behind a WRT54xx routers.
    As most of you know - this is not always a simple thing.
    My question is - what type of NAT the WRT54 routers use:
    full cone NAT, restricted cone NAT, port restricted cone NAT or symmetric NAT?
    (as described here
    As you can see - STUN is impossible when the NAT is of a "symmetric" type.
    Sometime the things work for me, sometimes - no. And i think the main reason is the NAT traversal trough the routers.
    Can you tell me what is the exact NAT type WRT routers use.
    Obviously, it can not be symmetric.
    Hope my question is not so stupid...
  2. HennieM

    HennieM Network Guru Member

    No wency, your question is not stupid, but I am, as it's the 1st time I hear all these ice cream terms...

    Most WRTs use Linux iptables for NAT, also known as IP Masquerading - an outgoing request from an internal IP/port gets to the router, where the router's external IP is put in place of the internal IP. When the reply comes back from the internet, the router's external IP is replaced by the internal one again, and the reply forwarded to the internal IP that made the original request.

    Port restriction and other such firewalling/filtering functions has very little to do with NAT, although it's effected by the same iptables software package.

    Dunno if that gives you a better idea - you can Google for "iptables" and/or "ipchains" which might provide a better conceptual description.
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