Disabled Iptables and SELinux. What else can interfere with incoming connections?

Question

linux

Good afternoon!
There is a server with public IP (not behind NAT) with Centos 6.5 installed. Installed and running Asterisk.
The problem is this: SIP clients get 408 Request Timeout when trying to connect.
SELinux is disabled, so is iptables. Port UDP / 5060, judging by netstat, obeys.
Question: what else can interfere with the connection?
Thank you for your attention!

Answer 1

check the files just in case:

/etc/hosts.deny
/etc/hosts.allow

iptables and selinux definitely not working?
Show the output of the commands:

iptables-save
sestatus

Answer 2

Client behind NAT?
What does asterisk itself say about this?
We tried to enable sip debug
Maybe the client is trying to connect and sends its local IP, the asterisk receives an incoming packet and sends a response to the local IP of the client, and not to the external
sip debug, you can enable both IP and client and see

Answer 3

There is also a wonderful failtoban service, it is just bundled with freepbx. Here he too can block through iptables. If it is enabled, then demolish it and also, just in case:

setenforce 0
iptables -F

Answer 4

It would be interesting to look at the network map, then you can give specific advice.!!!
But to begin with, I will advise this, based on the data that we have now.
Trace routes, prokinte port. somewhere along the way the port is closed. Faced with such a disaster.