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If you are using RHEL (Redhat), Fedora core or Cent os Linux just type following commands to disable the iptables firewall:

# service iptables save
# service iptables stop
# chkconfig iptables off

If you are using any other Linux distribution type the following command to clear up firewall rules:

# iptables -F
# iptables -X
# iptables -t nat -F
# iptables -t nat -X
# iptables -t mangle -F
# iptables -t mangle -X
# iptables -P INPUT ACCEPT
# iptables -P OUTPUT ACCEPT

You may need to put above rules in a shell script and execute the same. Also remove your iptables startup script from your network configuration file such as /etc/network/interfaces. Look for post-up directive.

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