Iptables Rule for Asterisk

The default iptables ruleset will block SIP traffic. To allow it, we
need below:

# SIP on UDP port 5060. Other SIP servers may need TCP port 5060 as well
iptables -A INPUT -p udp -m udp --dport 5060 -j ACCEPT
# RTP - the media stream
# (related to the port range in /etc/asterisk/rtp.conf)
iptables -A INPUT -p udp -m udp --dport 10000:20000 -j ACCEPT
#

Or we use -I to insert the rules at specified rule number (the topmost
rule is numbered 1)
iptables -I INPUT 2 -p udp -m udp --dport 5060 -j ACCEPT
iptables -I INPUT 2 -p udp -m udp --dport 10000:20000 -j ACCEPT