Symmetric NAT

Discussion in '3CX Phone System - General' started by xdgning, Sep 21, 2007.

  1. xdgning

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    Does 3CX work with symmetric NAT on any version? (free or commercial)

    I notice that one way to get around symmetric NAT is RTP proxying. Is 3CX capable of doing so?

    Thank.
     
  2. mdeerfield

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    It might :) using the STUN protocol. Here's a resource that you can look at that will explain in greater detail. This is an excerpt.

    "The STUN protocol enables a SIP client to discover whether it is behind a NAT, and to determine the type of NAT. STUN has received a lot of attention as a technique in the IETF, but suffers from a flaw, which means that it will only work with some NATs. In fact, STUN does not work with the type most commonly found in corporate networks - the symmetric NAT."

    http://www.newport-networks.com/whitepapers/nat-traversal3.html


    If I understand correctly - Your 3CX sever is sitting behind a Symmetric NAT and has a private IP address.. If not - please provide more details. What NAT/Router are you using in particular ?





     
  3. xdgning

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    Actually, it's the ATA that's behind the router, and all the router, 3CX and other ATAs are connected to the network.

    STUN only works for the other 3 type of NATs, but not for symmetric NAT, which most routers are using.

    I'm just wondering if 3CX can handle calls between users behind symmetric NAT in either the free version or the commercial version.
     
  4. xdgning

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    Anybody here? Help.... ^^
     
  5. dyntech

    dyntech New Member

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    I dont have an answer for your original question but, is it possible to do a VPN? That should eliminate any issues with STUN.
     
  6. archie

    archie Well-Known Member
    3CX Staff

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    It has been told many times, that use of UDP is not possible behind symmetric NAT at all. The possible solutions are to use VPN, or TCP connection.
     
  7. npiersma

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    Gents,

    As Archie stated, symetric NAT is killing for ANY SIP application. We've replaced our elcheapo firewall by a Cisco ASA 5505 and enabled SIP fix up. Since then we had NO problems related to any calls.

    When using a SIP provider, please make sure you've got a proper Firewall setup and realiable line (DSL/ADSL/SDSL) without to much overbooking.

    I agree with 3CX to have a proper local breakout to the PSTN installed in your local network.

    Niels
     

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