[libnice] ICE, NAT

[Youness Alaoui]

Hi,

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 :
http://en.wikipedia.org/wiki/Network_address_translation#Methods_of_port_translation
and see the difference between the full cone, the symmetric nat and the
restricted nats..
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.

I hope this helps,
Youness.



On Sat, Dec 6, 2014 at 7:51 AM, <fb111 at web.de> wrote:

>
> I would like to understand the following part out of the ICE RFC:
>
>
> "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."
>
>
>
> 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.
>
> 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?
>
> Thanks!
>
> Frank
>
>
>
>
> _______________________________________________
> nice mailing list
> nice at lists.freedesktop.org
> http://lists.freedesktop.org/mailman/listinfo/nice
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.freedesktop.org/archives/nice/attachments/20141209/91e90432/attachment.html>