I opened port 8245 for both inbound/outbound and tcp/udp traffic, but the noip2 updater continues to fail:

Sep 22 16:49:18 noip2[9326]: Can't gethostbyname for dynupdate.no-ip.com
Sep 22 16:49:18 noip2[9326]: Can't get our visible IP address from ip1.dynupdate.no-ip.com

My iptables rules to allow traffic on port 8245 (on eth0 internet interface) follow:

iptables -t filter -A INPUT -i eth0 -p tcp -m state --state NEW --dport 8245 -j ACCEPT
iptables -t filter -A INPUT -i eth0 -p udp --dport 8245 -j ACCEPT

iptables -t filter -A OUTPUT -o eth0 -p tcp -m state --state NEW --dport 8245 -j ACCEPT
iptables -t filter -A OUTPUT -o eth0 -p udp --dport 8245 -j ACCEPT

I asked no-ip support whether I had to allow ping requests on that interface and port, but they didn't mention anything about it in the response. They did confirm that the default port for the dns updater is 8245.

Thanks for your help.

The first line sas that the hostname can't be resolved to an ip. do a
dig dynupdate.no-ip.com
or
host dynupdate.no-ip.com
Seems like an DNS issue.

Dunno what the ports are good for but is this the machine connected to the WWW you have this iptables rules? If not you would need to set up some forwarding rules.

Thanks Zhjim,

From the excellent prompting received from your response in my other networking thread, I figured it out.

Due to my DROP policies, the following was necessary:

iptables -t filter -A OUTPUT -o eth0 -p tcp --dport 8245 -j ACCEPT

Works. :-)

Thank you very much for your time.

Cool did not even realize that I posted in two of your threads.
Good to see if solved and working.