Hello,

There seems to be a large number of discussions surrounding NAT traversal, as well as lots of documentation, but with no concrete answers. 

The NAT related wiki documentation is tedious, and depending on the outcome of this thread, I'd like to spend some time cleaning it up.

The most common problem (the same as ours) was having a router with broken ALG and a softphone that does not seem to work with STUN.

The following REGISTER is sent from a phone.

As you can see, the client's public IP is not specified anywhere. FreeSWITCH offers several ways around this, the main ones being;

* NDLB-connectile-dysfunction

* NDLB-force-rport

* apply-nat-acl

* sip-force-contact

The one that has worked in our case was "NDLB-connectile-dysfunction" (otherwise known as NAT HACK), however there seems to be a lot of negative comments about using this.

From what I can tell, the general argument is that NAT HACK is considered a non RFC compliant hack, and the SIP phones should be doing a better job of keeping to the RFCs.

In principle, this is a fair argument - but in practise, it's not a reasonable assumption that all phones are RFC compliant, and (imho) not a reasonable argument to have this functionality disabled by default.

So, I'd like to present the following arguments;

* Are there any other negative aspects about using NDLB-connectile-dysfunction, other than it is a non compliant RFC hack?

* Why is NDLB-connectile-dysfunction not enabled by default when certain conditions are met? In the event that FreeSWITCH receives a REGISTER from a phone specifying a Contact/Via as 192.168.0.0/16, but received on a public IP, then it should be obvious that NAT is broken and automatically try to circumvent it.

* People seem to get confused between server side and client side NAT problems, and that they both need to be resolved in a different way. The documentation doesn't seem to reflect this clearly.