<div dir="ltr"><div>Hi,<br></div><div><br></div><div>It will mainly depend on the type of NAT you are behind, some will simply block incoming traffic from an IP they never sent to before, while some will create a different port mapping for each destination. Basically, look at the types of NAT from here : <a href="http://en.wikipedia.org/wiki/Network_address_translation#Methods_of_port_translation">http://en.wikipedia.org/wiki/Network_address_translation#Methods_of_port_translation</a></div><div>and see the difference between the full cone, the symmetric nat and the restricted nats.. </div><div>In the case of port-restricted or symmetric nats, ICE would not work IF both peers are behind a symmetric or port-restricted NAT. Otherwise, A can't send to B, but B can send to A, which causes A to discover a remote peer-reflexive candidate and a new ICE check happens on a new candidate pair which would then allow A to send to B.</div><div><br></div><div>I hope this helps,</div><div>Youness.</div><div><br></div><div><br></div></div><div class="gmail_extra"><br><div class="gmail_quote">On Sat, Dec 6, 2014 at 7:51 AM, <span dir="ltr"><<a href="mailto:fb111@web.de" target="_blank">fb111@web.de</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div><div style="font-family:Verdana;font-size:12.0px"><div> </div>
<div>I would like to understand the following part out of the ICE RFC:</div>
<div> </div>
<div>
<pre style="font-size:1em;margin-top:0px;margin-bottom:0px;line-height:normal">"The second property is important for getting ICE to work when there
are NATs in front of L and R. Frequently, NATs will not allow
packets in from a host until the agent behind the NAT has sent a
packet towards that host. Consequently, ICE checks in each direction
will not succeed until both sides have sent a check through their
respective NATs."</pre>
<div> </div>
<div> </div>
<div>As far as I understand it, it says that even if your have discovered the server reflexive candidates from your signaling server of agent A and B after having sent the STUN requests/ answers, the two agents A and B can not communicate with each other because the NAT IP and port of the reflexive address is binded to the STUN servers IP address.</div>
<div> </div>
<div>and now this is my question: how are the two agents A and B are able to get a NAT IP & port binding for a communications between A and B directly? Do I understand the RFC correctly that A and B send "checks" to the agents A respectivley B NAT IP adress? How do A and B find out ech others port address so that they can communicate directly?</div>
<div> </div>
<div>Thanks!</div>
<div> </div>
<div>Frank</div>
<div> </div>
<div> </div>
<div> </div>
</div></div></div>
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<br></blockquote></div><br></div>