iptables for asterisk/SIP

#modprobe ip_conntrack_sip ip_nat_sip

#lsmod | grep ip_nat_sip
        ip_nat_sip              4288  0
        ip_conntrack_sip        6544  1 ip_nat_sip
        iptable_nat            20444  1 ip_nat_sip
        ip_conntrack           38808  3 ip_nat_sip,ip_conntrack_sip,iptable_nat 

Reglas iptables :

iptables -A INPUT -m state --state ESTABLISHED,RELATED -j ACCEPT
iptables -A INPUT -p udp --dport 5060 -j ACCEPT

Referencia : http://www.iptel.org/sipalg