Openning a port...doesn't work?!
 

Hello All,

I'm trying to open a port: 4900.

I have edited my /etc/services file by adding these two entries:

MyApp 4900/tcp
MyApp 4900/udp

I also have an application up and running that listens on this port.

When I check it with nmap:

# nmap -sS localhost

I don't see the port listed as open....????

Am I missing a step?

Any thoughts?

Do you see the port in use when you run:
netstat -nlp

Do you have a firewall running?
iptables -nL

netstat -nlp | grep 4900

tcp 0 0 :::4900 :::* LISTEN 6562/java

>>>>

iptables -nL | grep 4900

ACCEPT udp -- 0.0.0.0/0 0.0.0.0/0 udp dpt:4900
ACCEPT tcp -- 0.0.0.0/0 0.0.0.0/0 multiport dports x,x,x,x,x,x,x,4900


So I assume this part looks good...is it?

It should be so long as there are no other rules blocking it.

What "other" rules would there be?

If I have checked with netstat that the port is open and listening; and if I have checked the rules of the firewall(kernel)....what other rules or configs would I need to check in order to open that port?

Question 2 is...the check that I did with nmap, is that the right way to check the status of your ports to the outside world?

There may be other iptables rules.

nmap should be fine although results can sometimes be deceiving across some WANs and just because something is listening on a loopback address doesn't mean to say it is listening on specific network adresses..

How do I find out if there are other iptable rules AND how do I find out if there are "other" types of rules?

What other rules could overrule what is set by the services file and the firewall settings?

By the way, I'm running nmap locally (obviously cause I'm using localhost as a parameter) and I only have one NIC.

So, any thoughts why this is not working?

Anybody??

Just test your net app without firewall :

iptables -P INPUT ACCEPT
iptables -P OUTPUT ACCEPT
iptables -F
iptables -X

Then try nmap localhost

Try the following Nmap command:

># nmap -sS -p 4900 ip_address

I don't think 4900 is a port that's scanned by nmap automatically so you may have to specify it. Also the IP address should be the address that other computers will use to contact you.